Patent Publication Number: US-2023156883-A1

Title: Melanopic light system using cyan pumped white leds

Description:
FIELD OF THE INVENTION 
     The invention relates to a light generating system as well as to a lamp or luminaire comprising such light generating system. 
     BACKGROUND OF THE INVENTION 
     Solid state light emitting devices including adjustable melatonin suppressing effects are known in the art. U.S. Pat. No. 9,039,746, for instance, describes a solid state light emitting device include multiple LED components providing adjustable melatonin suppression effects. Multiple LED components may be operated simultaneously according to different operating modes according to which their combined output provides the same or similar chromaticity, but provides melatonin suppressing effects that differ by at least a predetermined threshold amount between the different operating modes. Switching between operating modes may be triggered by user input elements, timers/clocks, or sensors (e.g., photo sensors). Chromaticity of combined output of multiple LED components may also be adjusted, together with providing adjustable melatonin suppression effects at each selected combined output chromaticity. 
     SUMMARY OF THE INVENTION 
     Critical to our sleep/wake cycle is melatonin, a hormone that promotes sleep during night time. Melatonin is a sleep supportive hormone that we only produce around (and during) our usual bedtime. Light exposure during the evening and at night suppresses the natural production of melatonin. When the spectrum of the light is shifted towards lower CCT and intensity levels (like during dawn and dusk), this reduces melatonin suppression and makes the light less disruptive for sleep. During day time, natural daylight with high correlated color temperature (CCT, herein also indicated as “color temperature”) and intensity energizes people making them awake and alert. Current high performance LED based lighting apparatus with tunable CCT are able to mimic different phases of daylight, i.e., changes in spectral power distribution and variations in CCT, to a certain extent. 
     Next to the commonly known cones and rods, the human eye has melanopsin containing photoreceptors, affecting circadian entrainment and melatonin secretion, which are sensitive in a specific wavelength range. The relative spectral sensitivity for the classic receptors (rods and cones) and for the melanopic receptors are provided in  FIG.  6    (see also R. J. Lucas, et al., Measuring and using light in the melanopsin age, Trends in Neurosciences, Vol. 37, No. 1, January 2014, pp. 1-9; http://www.sciencedirect.com/science/article/pii/S0166223613001975, the report “CIE TN 003:2015: Report on the First International Workshop on Circadian and Neurophysiological Photometry, 2013” at http://cie.co.at/index.php?i_ca_id=978 (with a link to an excel toolbox http://files.cie.co.at/784_TN003_Toolbox.xls). If the spectral power in the melanopic wavelength range is absent or low, the light exposure will be less suppressive for the melatonin hormone production thus enabling faster sleep onset and more consolidated sleep. If the spectral power in the melanopic range is increased, a light exposure will result in stronger melatonin suppression. In general a light exposure can be said to be more biologically active and more alerting when the power in the melanopic range (and the ability to suppress melatonin at night) is increased. The effectiveness of a given light spectrum in suppressing melatonin production can be expressed in terms of the melanopsin effectiveness factor (MEF). This factor is calculated by multiplying the spectral power distribution of the light emitted by a lighting system (SPD(λ)) with the melanopic sensitivity function (m(λ)) divided by the product of SPD(λ) and the photopic luminosity function (V(λ)), normalized by the areas under the curves of m(λ) and V(λ), see equation 1 (and see also  FIG.  1   ). 
     
       
         
           
             
               
                 
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     Hence, the above indicated summations are over the visible range of 380-780 nm. By definition, the MEF for an equi-energy light source MEF EE  equals 1. Especially, an equi-energy light source has SPD(λ)=constant (for example 1) for all (visible) wavelengths. 
     The maximum sensitivity of this sensor in the human eye (intrinsically Photosensitive Retinal Ganglion Cells or iPRGCs) is around 490 nm. Stimulation of the iPRGCs during daytime (or the absence of stimulation in the evening) is important to control the circadian rhythm (entrainment to the 24 hours cycle). 
     The melanopic efficiency of a light spectrum can be calculated using the MDEF (Melanopic D65 Efficiency Factor) (sometimes also indicated as MDER, i.e. Melanopic Daylight Efficacy Ratio). In such instance, instead of an equal energy light source, a D65 source, i.e. CIE Standard Illuminant D65, which is a commonly used standard illuminant defined by the International Commission on Illumination (CIE). MDEF can be defined as the illuminance in lux of a D65 source needed to generate the same stimulation of the iPRGCs per lux of the test source (or test system). The MDEF value of a D65 source is approximately 0.906* the MEF value. Instead of the MDEF value, also the MELR value may be applied. The term MELR refers to melanopic efficacy of luminous radiation (in mW/Lm). 
     Instead of the MDEF value, also a MELR value (Melanopic efficacy of luminous radiation) may be used. With respect to the calculation of the MDEF value and the MELR value the following can be mentioned. For the test spectrum that is to be evaluated one may calculate how many mW are in the region of the spectrum of the test spectrum (by weighing the spectrum with m(lambda). One can also calculate how many Lm are generated. The ratio of power in mW and lumen in Lm is called MELR value. For a D65 reference spectrum this calculation can also be done. The MELR of D65=1.326 mW/Lm. The ratio of the MELR value of the test spectrum to be evaluated and the MELR value of the reference spectrum (D65) is called MDEF (or MDEF value). MDEF is a value without units. 
     MELR can thus be expressed in mW/Lm in which the mW is calculated by Σ λ=380   780  SPD(λ)m(λ)Δλ. The lumens in Lm are calculated in the normal way. 
     As indicated above, especially the MDEF, which is herein further indicated as MDER, is applied. The MDER is defined as: 
     
       
         
           
             
               
                 
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     wherein SPD(λ) is the spectral power distribution of the light emitted by a light generating device, m(λ) is the melanopic sensitivity function, the V(λ) is the photopic luminosity function. 
     As indicated above, the biological effect of lighting is the product of Illumination (Lux at the eye)*MDER*(Exposure time). Next to that also the time of exposure (morning/evening) determines the effect on people. In normal indoor lighting conditions, the stimulation of the IPRGCs during daytime is too low (e.g. 500 lux in offices, 4000K, MDER˜0.6). 
     It appears desirable to enrich lighting with cyan light. However, using direct cyan emitters in combination with white LEDs to boost the MDER of a spectrum may have one large drawback. The strongly deviating color point (the direct cyan emitter is not a white LED, but blueish/green), prohibits the application in lighting systems without enough (color) mixing. The approach using direct cyan emitters can therefore not be used in e.g. panels (side-lit or direct-lit), or in lighting systems using lenses. These problems may be reduced or even absent in the case that the light emitted by the cyan enhanced LED would be white. However, a tunable system using white LEDs in combination with a cyan pumped LED may enable only a very limited tuning range. In addition, it appears that a cyan pumped white LED with a deep-red phosphor with an emission peak intensity between 640 and 680 nm is very inefficient. 
     Hence, it is an aspect of the invention to provide an alternative lighting system, which preferably further at least partly obviates one or more of above-described drawbacks. The present invention may have as object to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative. 
     Hence, in a first aspect the invention provides a light generating system configured to generate system light. The light generating system comprises a first light generating device and a second light generating device. The first light generating device is configured to generate first device light. Especially, the first light generating device comprises (i) a first light source configured to generate first light source light having a first dominant wavelength λd 1 . In specific embodiments, the first dominant wavelength λd 1  is selected from the range of 470-500 nm. Further, especially the first light generating device comprises (ii) a first luminescent material configured to convert part of the first light source light into first luminescent material light. Especially, the first device light comprises the first light source light and the first luminescent material light. In specific embodiments, the first device light has a first color point. Yet further, the second light generating device is configured to generate second device light. Especially, the second light generating device comprises (i) a second light source configured to generate second light source light having a second dominant wavelength λd 2 . Further, especially the second light generating device comprises (ii) a second luminescent material configured to convert at least part of the second light source light into second luminescent material light. Especially, the second device light comprises the second luminescent material light and optionally the second light source light. In specific embodiments, the second device light has a second color point. Especially, the second device light is white light having a second correlated color temperature Tc 2 . Especially, in embodiments λd 1 -λd 2 ≥10 nm. Yet further, especially the spectral power distributions of the first light source light and the second light source light differ. In specific embodiments, the first color point and the second color point differ at maximum 0.03 for u′ and/or at maximum 0.03 for v′. Especially, the color points u′ and v′ are based on the 10° color matching functions according to CIE S 014-1/E:2006 (see table 2 of CIE S 014-1/E:2006) (herein also indicated as “10° CMFs” and similar phrases). Therefore, especially the invention provides in embodiments a light generating system configured to generate system light, wherein the light generating system comprises a first light generating device and a second light generating device, wherein: (a) the first light generating device is configured to generate first device light, wherein the first light generating device comprises (i) a first light source configured to generate first light source light having a first dominant wavelength λd 1  selected from the range of 470-500 nm, and (ii) a first luminescent material configured to convert part of the first light source light into first luminescent material light; wherein the first device light comprises the first light source light and the first luminescent material light; and wherein the first device light has a first color point; (b) the second light generating device is configured to generate second device light, wherein the second light generating device comprises (i) a second light source configured to generate second light source light having a second dominant wavelength λd 2 , and (ii) a second luminescent material configured to convert at least part of the second light source light into second luminescent material light; wherein the second device light comprises the second luminescent material light and optionally the second light source light; and wherein the second device light has a second color point (and wherein especially the second device light is white light having a second correlated color temperature Tc 2 ); (c) λd 1 -λd 2 ≥10 nm; (d) spectral power distributions of the first light source light and the second light source light differ; and (e) the first color point and the second color point differ at maximum 0.03 for u′ and/or at maximum 0.03 for v′ (using the 10° color matching functions according to CIE S 014-1/E:2006 (see table 2)). 
     Herein, color points are especially defined using the 10 degree color matching functions according to CIE S 014-1/E:2006 (see table 2). Color temperatures are based on the CIE 1960 diagram (u,v values, i.e. using the CIE 1931 2 degree color matching functions). 
     It appears that combining cyan pumped LEDs and blue pumped LEDs with the same color as the second channel allows to generate tunable systems with a large tuning range. In this way, a lighting system may be provided with a fixed or variable MDER, and also having a potentially variable correlated color temperature (CCT). Further, combining cyan pumped LEDs and blue pumped LEDs with the same color may also be used as such for providing a lighting system with an improved MDER as such. In this way, a lighting system may be provided with a fixed or variable MDER, with an essentially fixed correlated color temperature (CCT). 
     As indicated above, the invention provides a light generating system configured to generate system light, wherein the light generating system comprises a first light generating device and a second light generating device. 
     The term “first light generating device” may also refer to a plurality of essentially the same light generating devices (such as from the same bin). The term “second light generating device” may also refer to a plurality of essentially the same light generating devices (such as from the same bin). The terms “first light generating device” and “second light generating device” especially refers to devices that are different, especially in one or more spectral properties. Herein, the spectral distributions are different, and e.g. the color rendering indices (CRI) may differ substantially, such as at least 10 points. Hence, the spectral power distributions of the first light source light and the second light source light differ. However, the color points may essentially be the same. Hence, in embodiments the first color point and the second color point may differ at maximum 0.03 for u′ and/or at maximum 0.03 for v′, such as at maximum 0.02 for u′ and/or at maximum 0.02 for v′. Even more especially, in embodiments the first color point and the second color point may differ at maximum 0.01 for u′ and/or at maximum 0.01 for v′. For the u′ and v′ values, especially the 10° color matching functions according to CIE S 014-1/E:2006 (see table 2), are applied, i.e. the 10° color matching functions. Further, the phrase “the light generating system comprises a first light generating device and a second light generating device” does not exclude the presence of other light generating devices. As will be indicated below, in a number of embodiments, yet a further (a third) light generating device may be comprised by the light generating system. Instead of the term “light generating system” also the terms “lighting system” or “system” may herein be applied. Further, instead of the term “light generating device” also the terms “lighting device” or “device” may herein be applied. 
     Herein, the light generating devices especially comprise solid state light sources (see further also below). 
     As indicated above, the first light generating device and the second are substantially different, such as providing device light with different spectral power distributions. However, the color point may essentially be the same. Here below, some embodiments are described in relation to the first light generating device and second light generating device. 
     The first light generating device is configured to generate first device light. 
     Especially, the first light generating device comprises a first light source configured to generate first light source light having a first dominant wavelength λd 1 . The first light source especially comprises a solid state light source, such as an LED. The first dominant wavelength λd 1  is especially selected from the range of 470-500 nm. Hence, the first light source is especially a cyan light source, such as a cyan LED. More especially, the first dominant wavelength λd 1  may be selected from the range of 470-490 nm. Best results were obtained with first dominant wavelength λd 1  selected from the range of 475-485 nm. Even more especially, the first dominant wavelength λd 1  may be selected from the range of 478-484 nm, such as about 480 nm. 
     The first light generating device further comprises a first luminescent material configured to convert part of the first light source light into first luminescent material light. Hence, part of the first light source stays unconverted and may be part of the first device light. Hence, the first device light comprises the first light source light and the first luminescent material light. 
     In specific embodiments, the first luminescent material comprises a phosphor having a full width half maximum of at least 25 nm (such as in embodiments at least 50 nm) and having a peak wavelength selected from the range of 590-640 nm. Even more especially, the first luminescent material may be configured to convert part of the first light source light into first luminescent material light having a first luminescent material dominant wavelength λdL 1  selected from the range of 575-638 nm. In embodiments, the first luminescent material dominant wavelength λdL 1  selected from the range of 575-630 nm. Even more especially, the first luminescent material dominant wavelength λdL 1  selected from the range of 575-612 nm, such as about 577-605 nm, or even about 577-599 nm. With FWHMs of above about 50 nm, the first luminescent material dominant wavelength λdL 1  may especially be below about 612 nm, whereas with FWHMs of 30 nm or smaller, the first luminescent material dominant wavelength λdL 1  may especially be below about 638 nm. In embodiments, the first luminescent material dominant wavelength λdL 1  may be obtained with a single luminescent material. In yet other embodiments, the first luminescent material dominant wavelength λdL 1  may be obtained with two or more first luminescent materials, such as e.g. a plurality of different types of quantum dots. In specific embodiments, however, first device light may essentially consist of a single type of first light sources, such as cyan LEDs, and a single type of first luminescent materials. 
     Especially good results may be obtained when the first dominant wavelength λd 1  is selected from the range of 478-484 nm and wherein the first luminescent material dominant wavelength λdL 1  selected from the range of 575-638 nm, such as about 577-605 nm, even more especially selected from the range of about 577-599 nm. This may provide a desired color point in a relative energy efficient way. To this end, e.g. divalent europium containing nitrides may be applied, as known in the art (examples are indicated below). Alternatively or additionally, tetravalent manganese doped fluorides such as K 2 SiF 6 :Mn 4+ , or similar types of tetravalent manganese doped fluorides, can be applied. It especially appears that a combination of the first light source, such first luminescent material, and optionally one or more further first luminescent materials, such as of the cerium comprising garnet type, may be very useful for providing the first light generating device. 
     The term “first light source” may also refer to a plurality of essentially the same first light sources, such as solid state light sources from essentially the same bin. The term “first light source” may also refer to a plurality of different first light sources, though all complying with the herein indicated conditions. The term “first luminescent material” may also refer to a plurality of different luminescent materials. 
     Especially, the first device light is white light based on the color point using the 10° color matching functions. 
     In general, color points and correlated color temperatures are defined on the basis of 2° color matching functions (such as CIE 1931). As derived from the site https://www.konicaminolta.com/instruments/knowledge/color/part4/01.html the color sensitivity of the eye changes according to the angle of view (object size). The CIE originally defined the standard observer in 1931 using a 2 field of view, hence the name 2 Standard Observer. In 1964, the CIE defined an additional standard observer, this time based upon a 10° field of view; this is referred to as the 10 Supplementary Standard Observer. To give an idea of what a 2° field of view is like compared to a 10° field of view, at a viewing distance of 50 cm a 2° field of view would be a 1.7 cm circle while a 10° field of view at the same distance would be an 8.8 cm circle. The color matching functions are the tristimulus values of the equal-energy spectrum as a function of wavelength. These functions are intended to correspond to the sensitivity of the human eye. Separate sets of three color matching functions are specified for the 2° Standard Observer and 10° Supplementary Standard Observers. 
     Herein, CIE S 014-1/E:2006 see table 1 and 2, respectively, are therefore used. In view of user perception, it appears more useful to define the color point of the first device light using the 10° color matching function. For comparing the color point of the first device light and the second device light, the color points using the 10° color matching function are herein applied. Hence, to compare these color points, both color points should be defined on the basis of 10° color matching functions. For comparing the color points of the second device light and the third device light, herein in general the color points using the 2° color matching function is applied. This also allows ascribing a correlated color temperature. 
     Note that the second device light and the third device light using the 2° color matching function are in specific embodiments white light. As the color point of the first device light and the second device light using the 10° color matching function are essentially the same (differing at maximum 0.03 for u′ and/or at maximum 0.03 for v′, such as at maximum 0.02 for u′ and/or at maximum 0.02 for v′, yet even more especially at maximum 0.01 for u′ and/or at maximum 0.01 for v′, yet even more especially at maximum 0.005 for u′ and/or at maximum 0.005 for v′), de facto in embodiments the first device light is thus also white light and may be perceived as white light by the (10° Supplementary Standard) observer. 
     Especially assuming 2° color matching functions, the term “white light” herein, is known to the person skilled in the art. It especially relates to light having a correlated color temperature (CCT) between about 1800 K and 20000 K, such as between 2000 and 20000 K, especially 2700-20000 K, for general lighting especially in the range of about 2700 K and 6500 K. Yet further, in embodiments the correlated color temperature (CCT) is especially a color point within about 15 SDCM (standard deviation of color matching) from the BBL (black body locus), especially within about 10 SDCM from the BBL, even more especially within about 5 SDCM from the BBL. 
     Hence, the second device light is especially (such) white light. As, as indicated above the color points of the first device light and the second device light using the 10° color matching function are essentially the same, the first device light can also be indicated (in embodiments) as white light. 
     Further, the first device light has a first color point. Especially, in embodiments the color point is selected from the range of 0.18-0.24 for u′ and 0.4-0.53 for v′(using 10° CMFs). More especially, u′ may be selected from the range of 0.19-0.23, such as 0.195-0.22, more especially selected from the range of 0.195-0.205. More especially, v′ may be selected from the range of 0.41-0.52, more especially selected from the range of 0.43-0.50, such as especially selected from the range of 0.46-0.47 (using 10° CMFs). The former range equals about 20,000-3,500 K in the u′v′ CIE diagram of e.g. 1976. 
     Further, the first device light has a kind of first correlated color temperature Tc 1 . Hence, the first light generating device may be indicated as cool white light generating device. 
     The first light generating device may amongst others comprise a cyan LED as pump LED. Hence, the first light generating device may herein also be indicated as cyan LED or cyan PC LED. 
     The second light generating device is configured to generate second device light. 
     Especially, the second light generating device comprises a second light source configured to generate second light source light having a second dominant wavelength λd 2 . The second light source especially comprises a solid state light source, such as an LED. Especially, the second dominant wavelength λd 2  is smaller than the first dominant wavelength λd 1 . Hence, the first light source and the second light source are especially of different bins. In embodiments, λd 1 -λd 2 ≥10 nm. 
     The second light source may in embodiments be configured to generate visible light, especially blue light. Hence, in embodiments the second light source may especially be configured to generate first light source light having a second dominant wavelength λd 2  selected from the range of 430-470 nm (but at least smaller than the first dominant wavelength λd 1  (see also above)), such as at least 430 nm. In specific embodiments, λd 2 ≤465 nm. 
     Alternatively or additionally, the second light source may in embodiments be configured to generate light having an even shorter (dominant) wavelength. Hence, in embodiments the second light source may especially be configured to generate first light source light having a second dominant wavelength λd 2  selected from the range of 380-430 nm. 
     The second light generating device further comprises a second luminescent material configured to convert at least part of the second light source light into second luminescent material light. Hence, at least part of the second light source light may stay unconverted and may be part of the second device light. Hence, the second device light comprises the second luminescent material light and optionally the second light source light. As indicated above, there may be two main embodiments. In first embodiments, the second light source may be configured to generate blue light. In such embodiments, one or more luminescent materials, may be used to convert part of the second light source light into second luminescent material light. In second embodiments, the second light source may be configured to generate light source light which has a dominant wavelength lower than the (blue) wavelength range of 430-470 nm. In such embodiments, especially the light source light may be fully converted into luminescent material light. Hence, in such second embodiments the second light generating device may especially comprise two or more different luminescent materials. 
     The term “second light source” may also refer to a plurality of essentially the same second light sources, such as solid state light sources from essentially the same bin. The term “second light source” may also refer to a plurality of different second light sources, though all complying with the herein indicated conditions. The term “second luminescent material” may also refer to a plurality of different luminescent materials. 
     Especially, the second device light is white light, as its color point, determined as x,y in the CIE 1931 color diagram (2° CMF), or u′v′ in the CIE 1976 color diagram (in 2° CMF), is within 15 SDCM from the BBL, even more especially within about 10 SDCM from the BBL. 
     Further, the second device light has a second color point. Especially, in embodiments the second color point is selected from the range of 0.19-0.27 for u′ and 0.42-0.54 for v′ (in 2° CMF). More especially, second color point is selected from the range of 0.19-0.26 for u′ and 0.43-0.53 for v′ (in 2° CMF). For the second device light, it appears that the color point in 2° CMF or 10° CMF are substantially the same. Hence, in embodiments the second color point is selected from the range of about 0.19-0.27 for u′ and about 0.42-0.54 for v′ (in 10° CMF). More especially, second color point is selected from the range of about 0.19-0.26 for u′ and about 0.43-0.53 for v′ (in 10° CMF). 
     Further, the second device light may have a second correlated color temperature Tc 2 . Especially, in embodiments the second correlated color temperature Tc 2  may be selected from the range of 2700-6500 K, especially at least about 3000 K, even more especially at least about 3300 K, such as at least 3400 K. More especially, the second correlated color temperature Tc 2  may be at least 3500 K, such as even more especially at least about 4000 K. In yet further specific embodiments the second correlated color temperature Tc 2  may be selected from the range of at least 4500 K, such as at least 5000 K, like selected from the range of 5000-6500 K. Hence, the second light generating device may be indicated as cool white light generating device. 
     As indicated above, the spectral power distributions of the first light source light and the second light source light differ. However, the color points may essentially be the same (based on 10° CMF). Hence, in embodiments the first color point and the second color point may differ at maximum 0.03 for u′ and/or at maximum 0.03 for v′ (based on 10° CMF), such as at maximum 0.01 for u′ and/or at maximum 0.01 for v′, even more especially at maximum 0.005 for u′ and/or at maximum 0.005 for v′ (using based on 10° CMF). 
     Hence, in embodiments the light generating system may comprise one or more first light generating devices and one or more second light generating devices, and no further types of light generating devices (that may contribute to the system light). Hence, in such embodiments the system light may essentially consist of the first device light and the second device light. In specific embodiments, however, the light generating system may further comprise a system, configured to control the system light. In such embodiments, it may be possible to control the spectral power distribution of the system light, e.g. by controlling the power to the first light generating device and the second light generating device (e.g. individually). Hence, in such embodiments the system light may essentially consist of one or more of the first device light and the second device light. 
     The term “controlling” and similar terms especially refer at least to determining the behavior or supervising the running of an element. Hence, herein “controlling” and similar terms may e.g. refer to imposing behavior to the element (determining the behavior or supervising the running of an element), etc., such as e.g. measuring, displaying, actuating, opening, shifting, changing temperature, etc. Beyond that, the term “controlling” and similar terms may additionally include monitoring. Hence, the term “controlling” and similar terms may include imposing behavior on an element and also imposing behavior on an element and monitoring the element. The controlling of the element can be done with a control system, which may also be indicated as “controller”. The control system and the element may thus at least temporarily, or permanently, functionally be coupled. The element may comprise the control system. In embodiments, the control system and element may not be physically coupled. Control can be done via wired and/or wireless control. The term “control system” may also refer to a plurality of different control systems, which especially are functionally coupled, and of which e.g. one control system may be a master control system and one or more others may be slave control systems. A control system may comprise or may be functionally coupled to a user interface. 
     The control system may also be configured to receive and execute instructions form a remote control. In embodiments, the control system may be controlled via an App on a device, such as a portable device, like a Smartphone or I-phone, a tablet, etc. The device is thus not necessarily coupled to the lighting system, but may be (temporarily) functionally coupled to the lighting system. 
     Hence, in embodiments the control system may (also) be configured to be controlled by an App on a remote device. In such embodiments the control system of the lighting system may be a slave control system or control in a slave mode. For instance, the lighting system may be identifiable with a code, especially a unique code for the respective lighting system. The control system of the lighting system may be configured to be controlled by an external control system which has access to the lighting system on the basis of knowledge (input by a user interface of with an optical sensor (e.g. QR code reader) of the (unique) code. The lighting system may also comprise means for communicating with other systems or devices, such as on the basis of Bluetooth, WIFI, LiFi, ZigBee, BLE or WiMAX, or another wireless technology. 
     The system, or apparatus, or device may execute an action in a “mode” or “operation mode” or “mode of operation”. Likewise, in a method an action or stage, or step may be executed in a “mode” or “operation mode” or “mode of operation” or “operational mode”. The term “mode” may also be indicated as “controlling mode”. This does not exclude that the system, or apparatus, or device may also be adapted for providing another controlling mode, or a plurality of other controlling modes. Likewise, this may not exclude that before executing the mode and/or after executing the mode one or more other modes may be executed. 
     However, in embodiments a control system may be available, that is adapted to provide at least the controlling mode. Would other modes be available, the choice of such modes may especially be executed via a user interface, though other options, like executing a mode in dependence of a sensor signal or a (time) scheme, may also be possible. The operation mode may in embodiments also refer to a system, or apparatus, or device, that can only operate in a single operation mode (i.e. “on”, without further tunability). 
     Hence, in embodiments, the control system may control in dependence of one or more of an input signal of a user interface, a sensor signal (of a sensor), and a timer. The term “timer” may refer to a clock and/or a predetermined time scheme. 
     In yet further embodiments, the system may further comprise an input device selected from the group consisting of a user interface, a time device, and a sensor, wherein the control system may especially be configured to control a spectral power distribution of the system light in response to a signal of the input device. 
     The light generating system further comprises a third light generating device. 
     The third light generating device comprises a third light source configured to generate third light source light having a third dominant wavelength λd 3 . The third light source especially comprises a solid state light source, such as an LED. The third dominant wavelength λd 3  is smaller than the first dominant wavelength λd 1 , and λd 1 -λd 3 ≥10 nm. Hence, the first light source and the third light source are especially of different bins. 
     The third light source may in embodiments be configured to generate visible light, especially blue light. Hence, in embodiments the third light source may especially be configured to generate first light source light having a third dominant wavelength λd 3  selected from the range of 430-470 nm (but at least smaller than the first dominant wavelength λd 1  (see also above)), such as at least 430 nm. In specific embodiments, λd 3 ≤465 nm. 
     Alternatively or additionally, the third light source may in embodiments be configured to generate light having an even shorter (dominant) wavelength. Hence, in embodiments the third light source may especially be configured to generate first light source light having a third dominant wavelength λd 3  selected from the range of 380-430 nm. 
     The third light generating device further comprises a third luminescent material configured to convert at least part of the third light source light into third luminescent material light. Hence, at least part of the third light source light may stay unconverted and may be part of the third device light. Hence, the third device light comprises the third luminescent material light and optionally the third light source light. As indicated above, there may be two main embodiments. In first embodiments, the third light source may be configured to generate blue light. In such embodiments, one or more luminescent materials, may be used to convert part of the third light source light into third luminescent material light. In second embodiments, the third light source may be configured to generate light source light which has a dominant wavelength lower than the (blue) wavelength range of 430-470 nm. In such embodiments, especially the light source light may be fully converted into luminescent material light. Hence, in such third embodiments the third light generating device may especially comprise two or more different luminescent materials. 
     The term “third light source” may also refer to a plurality of essentially the same third light sources, such as solid state light sources from essentially the same bin. The term “third light source” may also refer to a plurality of different third light sources, though all complying with the herein indicated conditions. The term “third luminescent material” may also refer to a plurality of different luminescent materials. 
     Especially, the third device light is white light. 
     Further, the third device light has a third color point. Especially, in embodiments the color point is selected from the range of 0.22-0.30 for u′ and 0.46-0.54 for v′ (using 2° CMFs). More especially, in embodiments the color point is selected from the range of 0.23-0.29 for u′ and 0.47-0.53 for v′ (using 2° CMFs). For the third device light, it appears that the color point in 2° CMF or 10° CMF are substantially the same. Hence, in embodiments the color point is selected from the range of 0.22-0.30 for u′ and 0.46-0.54 for v′ (using 10° CMFs). More especially, in embodiments the color point is selected from the range of 0.23-0.29 for u′ and 0.47-0.53 for v′ (using 10° CMFs). 
     Assuming color points based on 2° CMFs u′ 2  (the u′ color coordinate of the second device light) is smaller than u′ 3  (the color coordinate of the third device light). Especially, u′ 3 -u′ 2 ≥0.01, especially u′ 3 -u′ 2 ≥0.02, even more especially u′ 3 -u′ 2 ≥0.03. Further, assuming color points based on 2° CMFs v′ 2  (the v′ color coordinate of the second device light) may be smaller than v′ 3  (the color coordinate of the third device light). Especially, v′ 3 -v′ 2 ≥0.01, especially v′ 3 -v′ 2 ≥0.02, even more especially v′ 3 -v′ 2 ≥0.03. In yet further specific embodiments, one or more (especially both) of the following applies: u′ 3 -u′ 2 ≥0.04 and v′ 3 -v′ 2 ≥0.04. 
     Further, the device light has a third correlated color temperature Tc 3 . Especially, in embodiments the third correlated color temperature Tc 3  is selected from the range of 2000-4000 K, such as especially selected from the range of 2700-3500, such as up to about 3400 K. 
     Especially, Tc 2 -Tc 3 ≥700 K, even more especially Tc 2 -Tc 3 ≥800 K, yet even more especially Tc 2 -Tc 3 ≥1000 K. Yet further, in specific embodiments, Tc 2 -Tc 3 ≥1300 K. As indicated above, the correlated color temperatures are especially defined on the basis of 2° CMF. 
     Hence, the third light generating device may be indicated as warm white light generating device. 
     As can be derived from the above, in embodiments, the spectral power distributions of the first light source light and the third light source light differ. 
     Hence, in embodiments the light generating system may comprise one or more first light generating devices, one or more second light generating devices, and one or more third light generating devices, and no further types of light generating devices (that may contribute to the system light). Hence, in such embodiments the system light may essentially consist of the first device light, the second device light, and the third device light. In specific embodiments, however, the light generating system may further comprise a system (see also above), configured to control the system light. In such embodiments, it may be possible to control the spectral power distribution of the system light, e.g. by controlling the power to the first light generating device, the second light generating device, and the third light generating device (e.g. individually). Hence, in such embodiments the system light may essentially consist of one or more of the first device light, the second device light, and the third device light. 
     Here below, some further embodiments are described. 
     In specific embodiments, the first light source light has a first dominant wavelength λd 1  selected from the range of 470-490 nm, the second light source light has a second dominant wavelength λd 2  selected from the range of 390-470 nm, and the third light source light has a third dominant wavelength λd 3  selected from the range of 390-470 nm. With such wavelength, in a relatively efficient way system light may be provided. 
     The term “light source” may refer to a semiconductor light-emitting device, such as a light emitting diode (LEDs), a resonant cavity light emitting diode (RCLED), a vertical cavity laser diode (VCSELs), an edge emitting laser, etc. The term “light source” may also refer to an organic light-emitting diode, such as a passive-matrix (PMOLED) or an active-matrix (AMOLED). In a specific embodiment, the light source comprises a solid state light source (such as a LED or laser diode). In an embodiment, the light source comprises a LED (light emitting diode). The term LED may also refer to a plurality of LEDs. Further, the term “light source” may in embodiments also refer to a so-called chips-on-board (COB) light source. The term “COB” especially refers to LED chips in the form of a semiconductor chip that is neither encased nor connected but directly mounted onto a substrate, such as a PCB. Hence, a plurality of semiconductor light sources may be configured on the same substrate. In embodiments, a COB is a multi LED chip configured together as a single lighting module. The term “light source” may also relate to a plurality of (essentially identical (or different)) light sources, such as 2-2000 solid state light sources. In embodiments, the light source may comprise one or more micro-optical elements (array of micro lenses) downstream of a single solid state light source, such as a LED, or downstream of a plurality of solid state light sources (i.e. e.g. shared by multiple LEDs). In embodiments, the light source may comprise a LED with on-chip optics. In embodiments, the light source comprises a pixelated single LEDs (with or without optics) (offering in embodiments on-chip beam steering). 
     The phrases “different light sources” or “a plurality of different light sources”, and similar phrases, may in embodiments refer to a plurality of solid state light sources selected from at least two different bins. Likewise, the phrases “identical light sources” or “a plurality of same light sources”, and similar phrases, may in embodiments refer to a plurality of solid state light sources selected from the same bin. 
     In specific embodiments, of the luminescent materials ( 210 , 220 , 230 ) comprise each phosphor, each configured to provide emission with each having a full width half maximum of at least 25 nm. For instance, one or more of the first luminescent material, the second luminescent material and the third luminescent material may comprise quantum dots. 
     In other embodiments, the second luminescent material and/or the third luminescent material comprise phosphors configured to provide luminescent material light ( 221 , 231 ) having a full width half maximum of at least 40 nm. Hence, in embodiments the second luminescent material light may have a FWHM of at least 40 nm. Alternatively or additionally, in embodiments the third luminescent material light may have a FWHM of at least 40 nm. 
     In embodiments, the second luminescent material comprises one or more of a cerium comprising garnet type luminescent material and a divalent europium based nitride material. Especially, both may be comprised by the second luminescent material. Alternatively or additionally, in embodiments, the third luminescent material comprises one or more of a cerium comprising garnet type luminescent material and a divalent europium based nitride material. Especially, both may be comprised by the third luminescent material. In yet further embodiments, the third luminescent material may (additionally) comprise a narrow band red emitting phosphor based on Mn 4+ . 
     When a luminescent material is applied herein, the luminescent material is especially configured downstream of a light source, such as in the above embodiment the white light emitting solid state light source. The light source may thus in embodiments be configured upstream of the luminescent material, with the luminescent material being configured to convert at least part of the light source light. The terms “upstream” and “downstream” relate to an arrangement of items or features relative to the propagation of the light from a light generating means (here the especially the light source), wherein relative to a first position within a beam of light from the light generating means, a second position in the beam of light closer to the light generating means is “upstream”, and a third position within the beam of light further away from the light generating means is “downstream”. 
     For green, yellow, orange, and/or red emitting luminescent material, e.g. inorganic luminescent material with activators or active species may be applied. Relevant active species may e.g. Eu 2+  or Ce 3+ . Other active species may be quantum dots. Yet other active species may be organic luminescent dyes. 
     In embodiments, luminescent materials may be selected from garnets and nitrides, especially doped with trivalent cerium or divalent europium, respectively. Embodiments of garnets especially include A 3 B 5 O 12  garnets, wherein A comprises at least yttrium or lutetium and wherein B comprises at least aluminum. Such garnets may be doped with cerium (Ce), with praseodymium (Pr) or a combination of cerium and praseodymium; especially however with Ce. Especially, B comprises aluminum (Al), however, B may also partly comprise gallium (Ga) and/or scandium (Sc) and/or indium (In), especially up to about 20% of Al, more especially up to about 10% of Al (i.e. the B ions essentially consist of 90 or more mole % of Al and 10 or less mole % of one or more of Ga, Sc and In); B may especially comprise up to about 10% gallium. In another variant, B and O may at least partly be replaced by Si and N. The element A may especially be selected from the group consisting of yttrium (Y), gadolinium (Gd), terbium (Tb) and lutetium (Lu). Further, Gd and/or Tb are especially only present up to an amount of about 20% of A. In a specific embodiment, the garnet luminescent material comprises (Y 1-x Lu x ) 3 B 5 O 12 :Ce, wherein x is equal to or larger than 0 and equal to or smaller than 1. 
     The term “:Ce”, indicates that part of the metal ions (i.e. in the garnets: part of the “A” ions) in the luminescent material is replaced by Ce. For instance, in the case of (Y 1-x Lu x ) 3 Al 5 O 12 :Ce, part of Y and/or Lu is replaced by Ce. This is known to the person skilled in the art. Ce will replace A in general for not more than 10%; in general, the Ce concentration will be in the range of 0.1 to 4%, especially 0.1 to 2% (relative to A). Assuming 1% Ce and 10% Y, the full correct formula could be (Y 0.1 Lu 0.89 Ce 0.01 ) 3 Al 5 O 12 . 
     Ce in garnets is substantially or only in the trivalent state, as is known to the person skilled in the art. 
     In embodiments, a red luminescent material may comprise one or more materials selected from the group consisting of (Ba,Sr,Ca)S:Eu, (Ba,Sr,Ca)AlSiN 3 :Eu and (Ba,Sr,Ca) 2 Si 5 N 8 :Eu. In these compounds, europium (Eu) is substantially or only divalent, and replaces one or more of the indicated divalent cations. In general, Eu will not be present in amounts larger than 10% of the cation; its presence will especially be in the range of about 0.5 to 10%, more especially in the range of about 0.5 to 5% relative to the cation(s) it replaces. The term “:Eu”, indicates that part of the metal ions is replaced by Eu (in these examples by Eu 2+ ). For instance, assuming 2% Eu in CaAlSiN 3 :Eu, the correct formula could be (Ca 0.98 Eu 0.02 )AlSiN 3 . Divalent europium will in general replace divalent cations, such as the above divalent alkaline earth cations, especially Ca, Sr or Ba. 
     The material (Ba,Sr,Ca)S:Eu can also be indicated as MS:Eu, wherein M is one or more elements selected from the group consisting of barium (Ba), strontium (Sr) and calcium (Ca); especially, M comprises in this compound calcium or strontium, or calcium and strontium, more especially calcium. Here, Eu is introduced and replaces at least part of M (i.e. one or more of Ba, Sr, and Ca). 
     Further, the material (Ba,Sr,Ca) 2 Si 5 N 8 :Eu can also be indicated as M 2 Si 5 N 8 :Eu, wherein M is one or more elements selected from the group consisting of barium (Ba), strontium (Sr) and calcium (Ca); especially, M comprises in this compound Sr and/or Ba. In a further specific embodiment, M consists of Sr and/or Ba (not taking into account the presence of Eu), especially 50 to 100%, more especially 50 to 90% Ba and 50 to 0%, especially 50 to 10% Sr, such as Ba 1.5 Sr 0.5 Si 5 N 8 :Eu (i.e. 75% Ba; 25% Sr). Here, Eu is introduced and replaces at least part of M, i.e. one or more of Ba, Sr, and Ca). 
     Likewise, the material (Ba,Sr,Ca)AlSiN 3 :Eu can also be indicated as MAlSiN 3 :Eu, wherein M is one or more elements selected from the group consisting of barium (Ba), strontium (Sr) and calcium (Ca); especially, M comprises in this compound calcium or strontium, or calcium and strontium, more especially calcium. Here, Eu is introduced and replaces at least part of M (i.e. one or more of Ba, Sr, and Ca). 
     Eu in the above indicated luminescent materials is substantially or only in the divalent state, as is known to the person skilled in the art. 
     The garnet type luminescent material may especially be applied as second and/or third luminescent material. 
     The term “luminescent material” herein especially relates to inorganic luminescent materials, which are also sometimes indicated as phosphors. These terms are known to the person skilled in the art. 
     The term “luminescent material” especially refers to a material that can convert first radiation, especially one or more of UV radiation and blue radiation, into second radiation. In general, the first radiation and second radiation have different spectral power distributions. Hence, instead of the term “luminescent material”, also the terms “luminescent converter” or “converter” may be applied. In general, the second radiation has a spectral power distribution at larger wavelengths than the first radiation, which is the case in the so-called down-conversion. In specific embodiments, however the second radiation has a spectral power distribution with intensity at smaller wavelengths than the first radiation, which is the case in the so-called up-conversion. In embodiments, the “luminescent material” may especially refer to a material that can convert radiation into e.g. visible and/or infrared light. For instance, in embodiments the luminescent material may be able to convert one or more of UV radiation and blue radiation, into visible light. The luminescent material may in specific embodiments also convert radiation into infrared radiation (IR). Hence, upon excitation with radiation, the luminescent material emits radiation. In general, the luminescent material will be a down converter, i.e. radiation of a smaller wavelength is converted into radiation with a larger wavelength (λ ex &lt;λ em ), though in specific embodiments the luminescent material may comprise down-converter luminescent material, i.e. radiation of a larger wavelength is converted into radiation with a smaller wavelength (λ ex &gt;λ em ). In embodiments, the term “luminescence” may refer to phosphorescence. In embodiments, the term “luminescence” may also refer to fluorescence. Instead of the term “luminescence”, also the term “emission” may be applied. Hence, the terms “first radiation” and “second radiation” may refer to excitation radiation and emission (radiation), respectively. Likewise, the term “luminescent material” may in embodiments refer to phosphorescence and/or fluorescence. The term “luminescent material” may also refer to a plurality of different luminescent materials. 
     As indicated above, in specific embodiments the light generating system may further optionally comprise a control system configured to control the first light generating device and the second light generating device. As the system may also comprise a third light generating device, in specific embodiments the light generating system may further comprise a control system configured to control the first light generating device, the second light generating device, and the third light generating device. Especially, in embodiments the control system may be configured to individually control two or more of the first light generating device, second light generating device, and the third light generating device. In this way, the spectral power distribution can be controlled, and concomitantly the MDER value may be controlled. 
     Further, with the present solution color differences between the cyan based light source and the second light generating device are substantially removed, as both may substantially emit device light with essentially the same color point (using 10° CMFs). Hence, the present invention also allows a simplification in the sense that the first light generation device and the second light generating device are controlled as set. Hence, in specific embodiments the control system may be configured to individually control (a) a set comprising the first light generating device and the second light generating device, and (b) the third light generating device. 
     For instance, this may also allow arranging the first light generating device and the second light generation device in a first string, and the third light generating device in a second string. 
     Hence, the light generating system comprises (i) a first LED string comprising one or more first light generating devices and one or more second light generating devices and (ii) a second LED string comprising one or more third light generating devices. 
     As indicated above, especially the light sources ( 10 , 20 , 30 ) comprise solid state light sources. 
     Especially, in embodiments the number n1 of first light generating devices plus the number n2 of second light generating devices may essentially be the same as the number n3 of third light generating devices. Hence, in specific embodiments (n1+n2)/n3=1. Then number n1 of first light generating devices plus the number n2 of second light generating devices in the first string may be chosen in dependence of e.g. the type of application. Especially, in embodiments a ratio of (a) number n1 of first light generating devices and (b) number n2 of second light generating devices with 0.05≤n1/n2≤20, though other values may also be possible. 
     Note that in specific embodiments the term “first string” may also refer to a plurality of electrically parallel arranged first strings. Note that in specific embodiments the term “second string” may also refer to a plurality of electrically parallel arranged second strings. 
     With the present invention, system light may be provided with a relatively high MDER. Further, this may be provided in a way that the color difference between a white LED and a cyan LED may not be an issue (see also above). 
     With respect to the MDER value, in an operational mode of the light generation system the system light may have an MDER value selected from the range of at least 0.45, even more especially at least 0.65, wherein MDER is defined as: 
     
       
         
           
             
               
                 
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     wherein SPD(λ) is the spectral power distribution of the system light, m(λ) is the melanopic sensitivity function, the V(λ) is the photopic luminosity function. 
     Further, in specific embodiments, in an operational mode of the light generation system the system light may have a CRI of at least 80. Yet further, in specific embodiments, in an operational mode of the light generation system the system light may have an R9 value of at least 50. Hence, in specific embodiments, in an operational mode of the light generation system the system light may have an MDER of at least 0.45, a CRI of at least 80, such as at least 85, and an R9 of at least 50. Especially, the system light may have an MDER of at least 0.65. 
     For instance, in embodiments the control system may be configured to control in an operational mode the spectral power distribution of the system light while maintaining a predefined MDER value. The term “predefined MDER value” may refer to a value or to a range of values. Especially, it may refer to a subset of an MDER range of 0.45-1.3, such as in the range of 0.65-0.89. MDER values larger than 1.3 may also be possible, but this may result in a less desirable CRI. 
     As indicated above, in embodiments the light generating system may further comprise an input device selected from the group consisting of a user interface, a time device, and a sensor. Especially, the control system (see also above) may be configured to control a spectral power distribution of the system light in response to a signal of the input device. For instance, at higher daylight levels, the system light may be reduced. For instance, later in the day, such as during the evening, the MDER value may be reduced. In embodiments, the MDER value may be made dependent upon the daylight level (and or the time of the day). Other embodiments may also be possible. Hence, especially the control system may be configured to control the spectral power distribution of the system light of the light generating system, such as the light generating system wherein the system comprises (i) a first LED string comprising one or more first light generating devices and one or more second light generating devices and (ii) a second LED string comprising one or more third light generating devices, such as in embodiments a light generating system comprising (i) a first LED string comprising one or more first light generating devices and one or more second light generating devices and (ii) a second LED string comprising one or more third light generating devices. 
     In yet a further aspect, the invention provides a lamp or a luminaire comprising the light generating system as defined herein. The luminaire may further comprise a housing, optical elements, louvres, etc. etc. . . . . The lamp or luminaire may further comprise a housing enclosing the first light generating device, the second light generating device, and the optional third light generating device. The lamp or luminaire may comprise a light window in the housing or a housing opening, through which the system light may escape from the housing. 
     The light generating system may be part of or may be applied in e.g. office lighting systems, household application systems, shop lighting systems, home lighting systems, accent lighting systems, spot lighting systems, theater lighting systems, fiber-optics application systems, projection systems, self-lit display systems, pixelated display systems, segmented display systems, warning sign systems, medical lighting application systems, indicator sign systems, decorative lighting systems, portable systems, automotive applications, (outdoor) road lighting systems, urban lighting systems, green house lighting systems, horticulture lighting, digital projection, or LCD backlighting. 
     The terms “blue light” or “blue emission” especially relates to light having a wavelength in the range of about 440-495 nm (including some violet and cyan hues). The terms “green light” or “green emission” especially relate to light having a wavelength in the range of about 495-570 nm. The terms “yellow light” or “yellow emission” especially relate to light having a wavelength in the range of about 570-590 nm. The terms “orange light” or “orange emission” especially relate to light having a wavelength in the range of about 590-620 nm. The terms “red light” or “red emission” especially relate to light having a wavelength in the range of about 620-780 nm. The term “pink light” or “pink emission” refers to light having a blue and a red component. 
     The terms “visible”, “visible light” or “visible emission” and similar terms refer to light having one or more wavelengths in the range of about 380-780 nm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which: 
         FIG.  1    shows spectral power distributions (normalized) of embodiments of first device light  111 , second device light  121 , and third device light  131 ; 
         FIG.  2    schematically depicts an embodiment of the light generating device comprising two strings of LEDs; 
         FIG.  3    shows shifts in spectral power distributions as function of different number of first light generating devices and second light generating devices in one of the strings; 
         FIG.  4    shows the result of calculations wherein shadings indicate the efficiency of power-balance luminaire (4400 lumen, LOR=0.9, 4000K) as a function of the number of cyan-red LEDs in the cool white channel (horizontal axis) and the flux at reference conditions of the cyan-red LED (left vertical axis); the labels on the bottom give the corresponding red phosphor used in the cyan-red LEDs (see table 1). The white dots represent the situations were CRI is above 80. The data labels give the melanopic-DER, CRI and R9. 
         FIGS.  5   a - 5   d    schematically depict a number of embodiments; 
         FIG.  6    shows the relative melanopic (m) (i.e. m(λ)) and V( 2 ) human eye sensitivity functions; and 
         FIG.  7    provides the 2° and 10° color matching functions (such as derived from CIE S 014-1/E:2006). 
     
    
    
     The schematic drawings are not necessarily to scale. 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In embodiments a direct cyan emitter may be replaced by a cyan pumped phosphor converted LED. The combination of cyan and a red phosphor can be used to generate cool white color points (e.g. 6500K). These LEDs may then be used in a 2 channel tunable system. For instance, the system may use warm white LEDs in one string and a combination of cyan-pumped LEDs and cool white LEDs in the second string. Especially, the color point of the cool white LED and the cyan-pumped LED may be essentially identical. The two cool white LEDs are spectrally extremely different (see  FIG.  1   ), resulting in e.g. a CRI difference of &gt;60. However, as the color points may essentially be the same they may appear the same when looking at them in on-state and may not give color shadows, even when combined with lenses. Since both types of the LEDs in the cyan enhanced string may have essentially identical color points, there may be more freedom to tune the cyan content in the final spectrum (e.g. 0-12 LEDs in steps of 1 can be varied, without problems with color inhomogeneity; see  FIGS.  2 - 3   ). Note that not necessarily 12 LEDs are applied. Other numbers may also be possible. 
     Referring to  FIG.  1   , in embodiments the first light source light  11  may have a first dominant wavelength λd 1  selected from the range of 470-490 nm. Further, the second light source light  21  may have a second dominant wavelength λd 2  selected from the range of 390-470 nm. Yet further, the third light source light  31  may have a third dominant wavelength λd 3  selected from the range of 390-470 nm. As also shown, in these embodiments, each of the luminescent materials comprises a phosphor, each configured to provide emission having a full width half maximum of at least 25 nm. In specific embodiments, the second luminescent material and the third luminescent material comprise phosphors configured to provide luminescent material light  221 , 231  having a full width half maximum of at least 40 nm. The third luminescent material may comprise a narrow band red emitting phosphor based on Me. However, also the second luminescent material may comprise a narrow band red emitting phosphor based on Me. Yet further, in specific embodiments also the first luminescent material may comprise a narrow band red emitting phosphor based on Me. In embodiments, however, the first luminescent material, the second luminescent material and the third luminescent material may comprise at least two different material compositions. This may relate to different weight ratios and/or different types of luminescent materials. 
       FIG.  2    schematically depicts an embodiment of a possible combination of strings. 
     In specific embodiments, see also  FIG.  2   , the light generating system  1000  may comprise (i) a first LED string  2100  comprising one or more first light generating devices  110  and one or more second light generating devices  120  and (ii) a second LED string  2200  comprising one or more third light generating devices  130 , wherein the light sources comprise solid state light sources. In embodiments, in one of the strings there may be a ratio of a number n1 of first light generating devices  110  and a number n2 of second light generating devices  120  of 0.05≤n1/n2≤20. In these embodiments, both strings have k light generating devices. Hence, in this embodiment k−n1=n2 second light generating devices  120 . The second string  2200  has k third light generating devices  130 . 
     The performance of a tunable system was calculated using different LED combinations. The warm white LED used in these cases has a CRI&gt;90 and a CCT of 3000 K).  FIG.  3    shows different spectra achievable for different n1/n2 for the same LED types (i.e.  1  cyan DWL—red phosphor combination for light generating device  110 ; see also  FIG.  1   ). 
     Several combinations of cyan DWL (dominant wavelength) and red phosphor were used in the calculations. The choice of the DWL of the cyan LED and the thickness i.e. extent of conversion of the red phosphor were adjusted to the choice of the red phosphor in order to stay close to the 6500K point on the BBL (here defined using 10° CMFs). 
     The performance of several different LED combinations was evaluated in the above described method, in particular making the cyan enhanced 6500K LED by different cyan DWL—red phosphor combinations: cyan DWLs 486, 487 and 489 nm with red phosphors PP 611, 620, 628 and 639 nm respectively. Here, DWL indicates the dominant wavelength and PP indicates the peak position. Amongst others, it appears that a system with CRI&gt;80 and melanopic-DER&gt;1 at 5000K is feasible, and that a system with CRI&gt;80 and MDER of ˜0.9 at 4200K is feasible. 
     The performance of the different options was calculated. Using a longer DWL cyan LED may require a deeper red phosphor to target the BBL. In principle a longer wavelength cyan LED fits better in the melanopic stimulation curve. Note that the amount of cyan light in the cyan-red spectrum decreases significantly, as we need to generate more red light to target ‘white’ light. These different cyan LEDs were used in a tunable system. The efficiency as a function of CCT and the number of cyan-red LEDs in the cool white string (total length=12) was calculated. The shorter the peak wavelength of the red phosphor in the cyan LED, the better the efficiency of the system (as expected). Surprisingly, the MDER of the system does not substantially depend on the choice of the cyan-red phosphor combination ( FIG.  4   ). For melanopic-DER, the choice of the cyan-red LED may be less important, for system efficiency it is best to choose the shortest possible red phosphor (and shorter DWL cyan LED). 
     Hence, combining cyan pumped LEDs and blue pumped LEDs with the same color as the second channel may allow to generate tunable systems with a large tuning range. 
     In  FIG.  4    shadings indicate the efficiency of power-balance luminaire (4400 lumen, LOR=0.9, 4000K) as a function of the number N of cyan-red LEDs in the cool white channel (vertical axis) and the flux (F) at reference conditions of the cyan-red LED (top horizontal axis); the labels on the bottom give the corresponding red phosphor used in the cyan-red LEDs, as indicated in the table below. From left to right the peak position decreases. The white dots represent the situations were CRI is above 80. The data labels give the melanopic-DER, CRI and R9. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
               
               
                 DWL 
                 Red phosphor 
                 DWL red 
                   
                   
                 Fraction 
                   
               
               
                 LED 
                 peak position 
                 phosphor 
                 Indication 
                 CE 
                 Cyan 
                 Relative 
               
               
                 (nm) 
                 (nm) 
                 (nm) 
                 in FIG. 4 
                 (max) 
                 left 
                 flux 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 480 
                 607 
                 591 
                 IV 
                 199.3 
                 0.509 
                 41.5 
               
               
                 480 
                 611 
                 593 
                   
                 186.5 
                 0.492 
                 38.8 
               
               
                 481 
                 620 
                 596 
                   
                 174.8 
                 0.487 
                 36 
               
               
                 483 
                 622 
                 599 
                 III 
                 169.6 
                 0.497 
                 34.3 
               
               
                 483 
                 628 
                 602 
                   
                 154.6 
                 0.471 
                 31.3 
               
               
                 484 
                 639 
                 606 
                 II 
                 129.2 
                 0.405 
                 25.9 
               
               
                 487 
                 660 
                 613 
                 I 
                 101 
                 0.334 
                 19.7 
               
               
                   
               
            
           
         
       
     
     Certainly for the CRI&gt;80 requirement, in the CCT region of interest (3000-5000K), the maximum MDER values can be achieved with all the cyan DWL—red phosphor combinations. But the LED efficiencies are different. The combination 480 nm-611 nm may provide the highest efficiency. 
     It was learned from perception testing that it is better to match the color points using 10° CMF. 
     Amongst others, the invention can also be used for light sources for static high melanopic stimulation. Then the cyan pumped white LED color point should be targeted at the same color point of the white LEDs for this static solution, most probably more likely around 4000 K. 
     Amongst others, the invention also provides a white light source with tunable melanopic stimulation i.e. high MDER at high CCT and low/normal MDER at low CCT by combining a string of warm white LEDs (string  1 ) and a second string consisting of cyan pumped LEDs combined with (blue pumped) cool white LEDs, in which: (a) the color point of the two LEDs in the cool white string are essentially identical; and (b) the number of cyan pumped LEDs/string may in specific embodiments e.g. be &gt;0 and &lt;8. Further, especially (c) the difference in CRI between the cyan pumped LED and the cool white LED is &gt;60. 
       FIG.  5   a    schematically depicts an embodiment of a light generating system  1000  configured to generate system light  1001 . The light generating system  1000  comprises a first light generating device  110  and a second light generating device  120 . 
     The first light generating device  110  is configured to generate first device light  111 . The first light generating device  110  comprises a first light source  10  configured to generate first light source light  11  having a first dominant wavelength λd 1  (e.g. selected from the range of 470-500 nm), and a first luminescent material  210  configured to convert part of the first light source light  11  into first luminescent material light  211 . 
     The first device light  111  comprises the first light source light  11  and the first luminescent material light  211 . 
     Especially, the first device light  111  may be white light having. Further, the first device light  111  has a first color point. Yet further, the first device light  111  may have a first correlated color temperature Tc 1 . 
     The first light generating device may especially be a cyan PC LED providing cool white. 
     The second light generating device  120  is configured to generate second device light  121 . The second light generating device  120  comprises a second light source  20  configured to generate second light source light  21  having a second dominant wavelength λd 2 , and a second luminescent material  220  configured to convert at least part of the second light source light  21  into second luminescent material light  221 . The second device light  121  comprises the second luminescent material light  221  and optionally the second light source light  21 . 
     Especially, the second device light  121  may be white light. The second device light  121  has a second color point. The second device light  121  may have a second correlated color temperature Tc 2 . 
     Especially, λd 1 -λd 2 ≥10 nm. In embodiments, λd 2 ≤465 nm. 
     As also shown in  FIG.  1   , the spectral power distributions of the first light source light  11  and the second light source light  21  differ. 
     Especially, the first color point and the second color point differ at maximum 0.03 for u′ and/or at maximum 0.03 for v′, such as at maximum 0.01 for u′ and/or at maximum 0.01 for v′, especially using the 10° color matching functions according to CIE S 014-1/E:2006 see table 2. 
     The second light generating device especially comprises a PC LED comprising a blue solid state light source (pump), configured to provide cool white light. 
     In embodiments, see also  FIG.  1   , the first dominant wavelength λd 1  is selected from the range of 478-484 nm. In embodiments, see also  FIG.  1   , the first luminescent material  210  is configured to convert part of the first light source light  11  into first luminescent material light  211  having a first luminescent material dominant wavelength λdL 1  selected from the range of 575-638 nm. 
     The lighting system light  1001  may in an operational mode especially comprise both the first device light  111  and the second device light  121 . Hence, lighting system light  1001  may in an operational mode especially comprise first light source light  11 , first luminescent material light  211 , second light source light  21 , and second luminescent material light  221 . 
       FIG.  5   b    schematically depicts an embodiment of the light generating system  1000  further comprising a third light generating device  130 . 
     The third light generating device  130  is configured to generate third device light  131 . The third light generating device  130  comprises a third light source  30  configured to generate third light source light  31  having a third dominant wavelength λd 3 , and a third luminescent material  230  configured to convert at least part of the third light source light  31  into third luminescent material light  231   
     The third device light  131  comprises the third luminescent material light  231  and optionally the third light source light  31 . 
     The third device light  131  may be white light. The third device light  131  has a third color point. The third device light  131  may have a third correlated color temperature Tc 3 . 
     Especially, in embodiments λd 1 -λd 3 ≥10 nm. In specific embodiments, λd 3 ≤465 nm. 
     As can also be seen in  FIG.  1   , the spectral power distributions of the first light source light  11  and the third light source light  31  differ. 
     Especially, the system light  1001  comprises one or more of the first device light  111 , the second device light  121 , and third device light  131 . 
     The lighting system light  1001  may in an operational mode especially comprise all of the first device light  111 , the second device light  121  and the third device light  131 . Hence, lighting system light  1001  may in an operational mode especially comprise first light source light  11 , first luminescent material light  211 , second light source light  21 , second luminescent material light  221 , third light source light  31  and third luminescent material light  231 . However, other embodiments may also be possible. 
     In specific embodiments, Tc 2 -Tc 3 ≥1000K. 
     The third light generating device especially comprises a PC LED comprising a blue solid state light source (pump) configured to provide warm white light. 
     As schematically depicted in  FIG.  5   c   , the light generating system  1000  may further comprising a control system  300  configured to control the first light generating device  110 , the second light generating device  120 , and the optional third light generating device  130 . 
     In embodiments, the control system  300  may be configured to individually control (a) a set comprising the first light generating device  110  and the second light generating device  120 , and (b) the third light generating device  130 ; see also  FIG.  2   . 
     The light generating system  1000  may further comprise an input device  350  selected from the group consisting of a user interface  351 , a time device  352 , and one or more sensors  353 . 
     The control system may especially be configured to control a spectral power distribution of the system light  1001  in response to a signal of the input device  350 . 
       FIG.  5   d    schematically depict embodiments of a lamp  1  (embodiment I) or a luminaire  2  (embodiment II) comprising the light generating system  1000 . In embodiment II, reference L indicates louvers. However, other embodiments may of course also be possible. 
       FIG.  6    shows the relative melanopic (m) (i.e. m(λ)) and photopic (V(λ)) human eye sensitivity functions. The maximum sensitivity for the melanopic function is at 490 nm, the full width half maximum values are at 447 nm and 531 nm, see also the accompanying table for the melanopic and photopic human eye sensitivity functions: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Photopic 
                 Melanopic 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 380 
                 0.000039 
                 0.000918 
               
               
                 381 
                 4.28264E−05 
                 0.001033 
               
               
                 382 
                 4.69146E−05 
                 0.001163 
               
               
                 383 
                 5.15896E−05 
                 0.00131 
               
               
                 384 
                 5.71764E−05 
                 0.001477 
               
               
                 385 
                 0.000064 
                 0.001667 
               
               
                 386 
                 7.23442E−05 
                 0.001883 
               
               
                 387 
                 8.22122E−05 
                 0.002129 
               
               
                 388 
                 9.35082E−05 
                 0.00241 
               
               
                 389 
                 0.000106136 
                 0.002729 
               
               
                 390 
                 0.00012 
                 0.003094 
               
               
                 391 
                 0.000134984 
                 0.003512 
               
               
                 392 
                 0.000151492 
                 0.003989 
               
               
                 393 
                 0.000170208 
                 0.004536 
               
               
                 394 
                 0.000191816 
                 0.005162 
               
               
                 395 
                 0.000217 
                 0.00588 
               
               
                 396 
                 0.000246907 
                 0.006705 
               
               
                 397 
                 0.00028124 
                 0.007651 
               
               
                 398 
                 0.00031852 
                 0.008739 
               
               
                 399 
                 0.000357267 
                 0.009989 
               
               
                 400 
                 0.000396 
                 0.011428 
               
               
                 401 
                 0.000433715 
                 0.013104 
               
               
                 402 
                 0.000473024 
                 0.015038 
               
               
                 403 
                 0.000517876 
                 0.017268 
               
               
                 404 
                 0.000572219 
                 0.019841 
               
               
                 405 
                 0.00064 
                 0.022811 
               
               
                 406 
                 0.00072456 
                 0.02624 
               
               
                 407 
                 0.0008255 
                 0.0302 
               
               
                 408 
                 0.00094116 
                 0.034773 
               
               
                 409 
                 0.00106988 
                 0.040055 
               
               
                 410 
                 0.00121 
                 0.046155 
               
               
                 411 
                 0.001362091 
                 0.051431 
               
               
                 412 
                 0.001530752 
                 0.057325 
               
               
                 413 
                 0.001720368 
                 0.06391 
               
               
                 414 
                 0.001935323 
                 0.071264 
               
               
                 415 
                 0.00218 
                 0.079477 
               
               
                 416 
                 0.0024548 
                 0.088645 
               
               
                 417 
                 0.002764 
                 0.098878 
               
               
                 418 
                 0.0031178 
                 0.110297 
               
               
                 419 
                 0.0035264 
                 0.123034 
               
               
                 420 
                 0.004 
                 0.137237 
               
               
                 421 
                 0.00454624 
                 0.146047 
               
               
                 422 
                 0.00515932 
                 0.155409 
               
               
                 423 
                 0.00582928 
                 0.16535 
               
               
                 424 
                 0.00654616 
                 0.175902 
               
               
                 425 
                 0.0073 
                 0.187096 
               
               
                 426 
                 0.008086507 
                 0.198964 
               
               
                 427 
                 0.00890872 
                 0.21154 
               
               
                 428 
                 0.00976768 
                 0.224858 
               
               
                 429 
                 0.01066443 
                 0.238954 
               
               
                 430 
                 0.0116 
                 0.253865 
               
               
                 431 
                 0.01257317 
                 0.266176 
               
               
                 432 
                 0.01358272 
                 0.279 
               
               
                 433 
                 0.01462968 
                 0.29235 
               
               
                 434 
                 0.01571509 
                 0.306239 
               
               
                 435 
                 0.01684 
                 0.320679 
               
               
                 436 
                 0.01800736 
                 0.335684 
               
               
                 437 
                 0.01921448 
                 0.351265 
               
               
                 438 
                 0.02045392 
                 0.367435 
               
               
                 439 
                 0.02171824 
                 0.384205 
               
               
                 440 
                 0.023 
                 0.401587 
               
               
                 441 
                 0.02429461 
                 0.415459 
               
               
                 442 
                 0.02561024 
                 0.429639 
               
               
                 443 
                 0.02695857 
                 0.444126 
               
               
                 444 
                 0.02835125 
                 0.458915 
               
               
                 445 
                 0.0298 
                 0.474003 
               
               
                 446 
                 0.03131083 
                 0.489382 
               
               
                 447 
                 0.03288368 
                 0.505051 
               
               
                 448 
                 0.03452112 
                 0.520999 
               
               
                 449 
                 0.03622571 
                 0.537223 
               
               
                 450 
                 0.038 
                 0.553715 
               
               
                 451 
                 0.03984667 
                 0.56863 
               
               
                 452 
                 0.041768 
                 0.583694 
               
               
                 453 
                 0.043766 
                 0.598893 
               
               
                 454 
                 0.04584267 
                 0.614217 
               
               
                 455 
                 0.048 
                 0.629654 
               
               
                 456 
                 0.05024368 
                 0.645191 
               
               
                 457 
                 0.05257304 
                 0.660812 
               
               
                 458 
                 0.05498056 
                 0.676507 
               
               
                 459 
                 0.05745872 
                 0.692256 
               
               
                 460 
                 0.06 
                 0.708048 
               
               
                 461 
                 0.06260197 
                 0.723532 
               
               
                 462 
                 0.06527752 
                 0.739008 
               
               
                 463 
                 0.06804208 
                 0.75446 
               
               
                 464 
                 0.07091109 
                 0.769869 
               
               
                 465 
                 0.0739 
                 0.785216 
               
               
                 466 
                 0.077016 
                 0.800481 
               
               
                 467 
                 0.0802664 
                 0.815643 
               
               
                 468 
                 0.0836668 
                 0.830679 
               
               
                 469 
                 0.0872328 
                 0.845571 
               
               
                 470 
                 0.09098 
                 0.86029 
               
               
                 471 
                 0.09491755 
                 0.872405 
               
               
                 472 
                 0.09904584 
                 0.88423 
               
               
                 473 
                 0.1033674 
                 0.89574 
               
               
                 474 
                 0.1078846 
                 0.906916 
               
               
                 475 
                 0.1126 
                 0.917734 
               
               
                 476 
                 0.117532 
                 0.928169 
               
               
                 477 
                 0.1226744 
                 0.938197 
               
               
                 478 
                 0.1279928 
                 0.947794 
               
               
                 479 
                 0.1334528 
                 0.956938 
               
               
                 480 
                 0.13902 
                 0.965604 
               
               
                 481 
                 0.1446764 
                 0.971753 
               
               
                 482 
                 04504693 
                 0.977347 
               
               
                 483 
                 04564619 
                 0.98237 
               
               
                 484 
                 04627177 
                 0.9868 
               
               
                 485 
                 04693 
                 0.990622 
               
               
                 486 
                 04762431 
                 0.993814 
               
               
                 487 
                 04835581 
                 0.996364 
               
               
                 488 
                 04912735 
                 0.998254 
               
               
                 489 
                 0499418 
                 0.999471 
               
               
                 490 
                 0.20802 
                 1 
               
               
                 491 
                 0.2171199 
                 0.999832 
               
               
                 492 
                 0.2267345 
                 0.998957 
               
               
                 493 
                 0.2368571 
                 0.997369 
               
               
                 494 
                 0.2474812 
                 0.995059 
               
               
                 495 
                 0.2586 
                 0.992021 
               
               
                 496 
                 0.2701849 
                 0.988257 
               
               
                 497 
                 0.2822939 
                 0.983766 
               
               
                 498 
                 0.2950505 
                 0.978548 
               
               
                 499 
                 0.308578 
                 0.972608 
               
               
                 500 
                 0.323 
                 0.965951 
               
               
                 501 
                 0.3384021 
                 0.958588 
               
               
                 502 
                 0.3546858 
                 0.950526 
               
               
                 503 
                 0.3716986 
                 0.941781 
               
               
                 504 
                 0.3892875 
                 0.932367 
               
               
                 505 
                 0.4073 
                 0.9223 
               
               
                 506 
                 0.4256299 
                 0.911597 
               
               
                 507 
                 0.4443096 
                 0.900281 
               
               
                 508 
                 0.4633944 
                 0.888376 
               
               
                 509 
                 0.4829395 
                 0.875903 
               
               
                 510 
                 0.503 
                 0.862887 
               
               
                 511 
                 0.5235693 
                 0.848186 
               
               
                 512 
                 0.544512 
                 0.833038 
               
               
                 513 
                 0.56569 
                 0.817476 
               
               
                 514 
                 0.5869653 
                 0.80153 
               
               
                 515 
                 0.6082 
                 0.785234 
               
               
                 516 
                 0.6293456 
                 0.768617 
               
               
                 517 
                 0.6503068 
                 0.751716 
               
               
                 518 
                 0.6708752 
                 0.734563 
               
               
                 519 
                 0.6908424 
                 0.71719 
               
               
                 520 
                 0.71 
                 0.699628 
               
               
                 521 
                 0.7281852 
                 0.681754 
               
               
                 522 
                 0.7454636 
                 0.663768 
               
               
                 523 
                 0.7619694 
                 0.645696 
               
               
                 524 
                 0.7778368 
                 0.62757 
               
               
                 525 
                 0.7932 
                 0.609422 
               
               
                 526 
                 0.8081104 
                 0.59128 
               
               
                 527 
                 0.8224962 
                 0.573171 
               
               
                 528 
                 0.8363068 
                 0.555121 
               
               
                 529 
                 0.8494916 
                 0.537159 
               
               
                 530 
                 0.862 
                 0.519309 
               
               
                 531 
                 0.8738108 
                 0.501594 
               
               
                 532 
                 0.8849624 
                 0.484037 
               
               
                 533 
                 0.8954936 
                 0.466662 
               
               
                 534 
                 0.9054432 
                 0.449487 
               
               
                 535 
                 0.9148501 
                 0.432534 
               
               
                 536 
                 0.9237348 
                 0.41582 
               
               
                 537 
                 0.9320924 
                 0.399364 
               
               
                 538 
                 0.9399226 
                 0.383183 
               
               
                 539 
                 0.9472252 
                 0.367292 
               
               
                 540 
                 0.954 
                 0.351707 
               
               
                 541 
                 0.9602561 
                 0.336519 
               
               
                 542 
                 0.9660074 
                 0.321656 
               
               
                 543 
                 0.9712606 
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       FIG.  7    provides the 2° and 10° color matching functions (such as derived from CIE S 014-1/E:2006). 
     The term “plurality” refers to two or more. 
     The terms “substantially” or “essentially” herein, and similar terms, will be understood by the person skilled in the art. The terms “substantially” or “essentially” may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in embodiments the adjective substantially or essentially may also be removed. Where applicable, the term “substantially” or the term “essentially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. 
     The term “comprise” includes also embodiments wherein the term “comprises” means “consists of”. 
     The term “and/or” especially relates to one or more of the items mentioned before and after “and/or”. For instance, a phrase “item  1  and/or item  2 ” and similar phrases may relate to one or more of item  1  and item  2 . The term “comprising” may in an embodiment refer to “consisting of” but may in another embodiment also refer to “containing at least the defined species and optionally one or more other species”. 
     Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein. 
     The devices, apparatus, or systems may herein amongst others be described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation, or devices, apparatus, or systems in operation. 
     It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. 
     In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. 
     Use of the verb “to comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”. 
     The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. 
     The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a device claim, or an apparatus claim, or a system claim, enumerating several means, several of these means may be embodied by one and the same item of hardware. 
     The invention also provides a control system that may control the device, apparatus, or system, or that may execute the herein described method or process. Yet further, the invention also provides a computer program product, when running on a computer which is functionally coupled to or comprised by the device, apparatus, or system, controls one or more controllable elements of such device, apparatus, or system. 
     The invention further applies to a device, apparatus, or system comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. 
     The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications.