Patent Publication Number: US-8981637-B2

Title: Light source having particular spectral power distribution as function of wavelength

Description:
FIELD OF THE INVENTION 
     The invention relates to a light source and the use of the light source for functional lighting. 
     BACKGROUND OF THE INVENTION 
     Over the last years, it has became more and more evident that artificial night lighting can have negative consequences for animals, especially for those who are active between dusk and dawn. Of course, different species react differently to different spectra of light; the dependence of these reactions on the spectral light distribution is, however, unknown for the vast majority of animal species, but it is possible to discern certain groups or trends. Many species are disturbed more by short wavelength light. This can have effects on the biological clock of both animals and humans, can influence the adaptation of the eyes to light or dark, or can influence behavior. Insects, for instance, are known to be more attracted by short wavelength light than by light of longer wavelengths. Bats show a lower avoidance of long wavelength light and rodents seem to perceive long wavelength light as darkness. 
     Another, well known example are sea turtles, where the females will not release their eggs on beaches with a lot of short wavelength light and where the young turtles emerging from the eggs are attracted to short wavelength light from inland instead of crawling towards the sea. The negative effects of lighting near ocean beaches on sea turtles have prompted cities to create ordinances which limit or restrict lighting near ocean beaches. These ordinances may require that light fixtures be turned off in some circumstances. Indeed, in or near protected habitats, all kinds of possible disturbances to animals should be kept to a minimum. But when the possible effects of accidents, involving human lives and direct effects on the environment as in traffic accidents or industrial calamities leading to chemical spills, fires, etc., outweigh the possible environmental effects, necessary precautions should be taken. One of the possible precautions is to have sufficient lighting for work and transport safety. 
     In an attempt to meet both the demand of lighting being not or hardly disturbing to animals and the demand of safety to humans, WO2005/107336 discloses a luminaire with two light sources. The luminaire is capable of selectively operating either a more or less monochromatic light source, not being disruptive to sea turtles and emitting in a wavelength range between 590 and 650 nm (for example a neon lamp radiating at wavelengths starting at around 585 nm), or an incandescent/fluorescent light source emitting light that is disruptive to sea turtles but pleasant and providing safety to humans. It is a disadvantage of the known light source/luminaire that it is rather expensive and relatively complex of construction. Another disadvantage of the known light source/luminaire is that it produces unpleasant light which only contributes to a relatively low extent to the safety of humans when the luminaire operates said monochromatic light source. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to counteract at least one of the above-mentioned disadvantages. To achieve this, the light source according to the invention has the following features for generating light having a spectral emittance in at least a part of the range of 380 nm to 680 nm: 
     the light has a spectral power distribution E(λ) as a function of the wavelength λ; the light source comprises a lighting control element and at least one additional lighting control element, the lighting control element and the at least one additional lighting control element being set to obtain generated light with a power distribution over a first range of 600 nm&lt;=λ&lt;680 nm, a second range of 505 nm&lt;=λ&lt;600 nm, and a third range of 380 nm&lt;=λ&lt;505 nm, wherein a first ratio of the integral power distribution over said first range to that of a range of 380 nm&lt;=λ&lt;=680 nm is given by the relation: 
     
       
         
           
             
               
                 
                   
                     ∫ 
                     600 
                     680 
                   
                   ⁢ 
                   
                     
                       E 
                       ⁡ 
                       
                         ( 
                         λ 
                         ) 
                       
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       ⅆ 
                       λ 
                     
                   
                 
                 
                   
                     ∫ 
                     380 
                     680 
                   
                   ⁢ 
                   
                     
                       E 
                       ⁡ 
                       
                         ( 
                         λ 
                         ) 
                       
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       ⅆ 
                       λ 
                     
                   
                 
               
               = 
               
                 
                   
                     P 
                     1 
                   
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   wherein 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   0.65 
                 
                 &lt;= 
                 
                   P 
                   1 
                 
                 &lt;= 
                 0.95 
               
             
             , 
           
         
       
     
     a second ratio of the integral power distribution over said second range to that of a range of 380 nm&lt;=λ&lt;=680 nm is given by the relation: 
     
       
         
           
             
               
                 
                   
                     ∫ 
                     505 
                     600 
                   
                   ⁢ 
                   
                     
                       E 
                       ⁡ 
                       
                         ( 
                         λ 
                         ) 
                       
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       ⅆ 
                       λ 
                     
                   
                 
                 
                   
                     ∫ 
                     380 
                     680 
                   
                   ⁢ 
                   
                     
                       E 
                       ⁡ 
                       
                         ( 
                         λ 
                         ) 
                       
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       ⅆ 
                       λ 
                     
                   
                 
               
               = 
               
                 
                   
                     P 
                     m 
                   
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   wherein 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     P 
                     m 
                   
                 
                 &gt;= 
                 0.08 
               
             
             , 
           
         
       
     
     a third ratio of the integral power distribution over said third range to that of a range of 380 nm&lt;=λ&lt;=680 nm is given by the relation: 
     
       
         
           
             
               
                 
                   ∫ 
                   380 
                   505 
                 
                 ⁢ 
                 
                   
                     E 
                     ⁡ 
                     
                       ( 
                       λ 
                       ) 
                     
                   
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ⅆ 
                     λ 
                   
                 
               
               
                 
                   ∫ 
                   380 
                   680 
                 
                 ⁢ 
                 
                   
                     E 
                     ⁡ 
                     
                       ( 
                       λ 
                       ) 
                     
                   
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ⅆ 
                     λ 
                   
                 
               
             
             = 
             
               
                 
                   P 
                   s 
                 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 wherein 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   P 
                   s 
                 
               
               &gt;= 
               
                 0.03 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 or 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   P 
                   s 
                 
               
               &gt;= 
               
                 0.015 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 if 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   P 
                   1 
                 
               
               &lt;= 
               0.75 
             
           
         
       
     
     each of the first, second and third range has a spectral coverage by the lighting control element respectively the at least one additional lighting control element of at least 10%. In a wavelength range between 680 nm and 780 nm of visible radiation, an emission of spectral power should be relatively low, i.e. 25% or less relative to the spectral power emitted from 380 nm to 780 nm, to render the lamp to be efficient. Preferably said emission shall not be more than 10% relative to the spectral power emitted from 380 nm to 780 nm in order to anticipate on future environmental demands on lamp efficiency. Most preferably the emitted spectral power in the range 680 nm to 780 nm is practically absent, for example 2% or less relative to the spectral power emitted from 380 nm to 780 nm. 
     Spectral coverage is to be understood as the fraction of a specific range in which the lighting control elements have an emission. A lighting control element is considered to have an emission at a certain wavelength if the measured intensity at said wavelength is at least ten times the amount of the background noise signal at that wavelength as measured when the light source is switched off. The present invention provides a light source that controls the emitted light so as to offer a sufficient level of vision to humans for performing their tasks in a safe manner, and that simultaneously results in relatively very little disturbance to short wavelength-sensitive animals. For humans, lighting needs to have certain qualities to be effective. The ability to recognize colors is very important in work safety, for example in recognizing safety and warning signs, localizing safety equipment, recognizing tubing and product labels and for observing processes. Besides this, a sufficient level of color rendering also aids in recognizing people and enhances spatial orientation, both contributing to a general feeling of comfort and safety, but particularly important in emergency situations. For white light, or at least light with a color point relatively close to the black body line, and with a moderate to good color rendering, the CIE defined a measure for color rendering quality, the CRI, or Ra. In defining the Ra, an incandescent lamp was defined as having a Ra of 100 and a now probably obsolete “warm white” calcium halophosphate fluorescent lamp was defined to have a Ra of 50. The CIE defines the ‘color rendering properties’ of a light source as the ‘Effect of a light source on the color appearance of objects in comparison with their color appearance under a reference illuminant for specified conditions’, “CIE-Publikation Nr. 13.3, 1995, Method of Measuring and Specifying Colour-rendering Properties of Light Sources”. Although this is of great practical importance and of great esthetical value in many cases, in many applications it is sufficient for humans to discern and recognize certain colors, without the need to compare or differentiate between different shades of similar colors. A sufficient level of color recognition by humans in this respect means the ability of humans to recognize, and distinguish between, the basic colors of objects illuminated by a light source. If, for example, the spectral coverage in the third range is increased from the above-mentioned at least 10% to at least 20% coverage, the color rendering Ra is increased by about 20 points and safety to humans is increased. The basic colors are generally seen as the color category comprising for example black, grey, white, pink, red, orange, yellow, green, blue, purple, brown, and azure. To offer good color recognition the spectrum does not have to be completely filled over the complete range of light wavelengths, although a certain distribution in the spectral power distribution is preferred to make each color visible and to counteract metamerism. In the emission spectrum of the lamp, the minimal values for the second ratio P m  is at least 0.08 and the third ratio P s  at least 0.015 or 0.03, depending on the first ratio P l . These minimal values ensure that sufficient radiation is present in the medium, i.e. 505 nm to 600 nm (green to orange), and short, i.e. 380 nm to 505 nm (indigo to green) wavelength ranges to attain the possibility of color recognition, in combination with the specified minimum spectral coverage value. If both the P s  and P l  ratios become too small, the medium wavelength range P m  is too dominant and contravenes with color recognition. Therefore, the lower limit of the amount of emission in the short wavelength range P s  should be balanced against the emission in the medium wavelength range P m  and against the emission in the long wavelength range P l , with respect to color recognition and disturbance to animals. This is attained by the shift in the criterion of P s &gt;=0.03 for P l &gt;=0.65 to Ps&gt;=0.015 for P l &gt;=0.75. In terms of CRI expressed as R a8 , this ensures a value of at least 35. To counteract P m  being too dominant, the light source preferably is characterized in that P m &lt;=0.32, more preferably P m &lt;=0.25, even more preferably P m &lt;=0.20. Emission spectra of lamps wherein a first ratio P l  of the integral power distribution over said first range of 600 nm&lt;=λ&lt;=680 nm (orange to red range) to that of a range of 380 nm&lt;=λ&lt;=680 nm (wavelength range visible to human) is higher than 0.9 will result in insufficient possibilities of color recognition. 
     An embodiment of the light source is characterized in that 0.65&lt;=P l &lt;=0.85, preferably 0.70&lt;=P l &lt;=0.85. Based on our current insights into the influence of spectral power distribution on the attractiveness of artificial light to insects, it is seen that P l &gt;=0.65 of the power of the emitted light between 600 and 680 nm, would result in a reduction in insect attraction by 50%, compared to the most commonly used white light sources, with a P l  between 0.20 and 0.40. A further increase in long wavelength radiation P l &gt;=0.70 would decrease insect attraction to below 10%. For the less general, more light sensitive bats, like the Myotis species, P l &gt;=0.70 allows formulating a spectral power distribution which, based on our current knowledge, does not result in a significant disturbance, but does allow reaching street lighting levels corresponding to the lower light level classes S5, S6, A2, A3. Taking into account the other requirements on the spectral power distribution stated here, with P l &gt;=0.80 a spectrum can be obtained which, compared at equal flux levels, is less attractive to insects than a monochromatic Low Pressure Sodium lamp, yet with a color rendering index of more than 60. 
     Another embodiment of the light source is characterized in that the total flux of the light source is at least 100 lm, preferably at least 250 lm, more preferably at least 750 lm. A lumen package of 100 lm is suitable for lighting specific points in a professional setting, e.g. a warning sign, an entrance or an obstacle. From 250 lm, such a light source could be used for lighting in public or private gardens. At fluxes higher than 750 lm, for example up to the order of magnitude of 100000 lm, such light sources/luminaires can be applied for street, road and area lighting. 
     In an embodiment, the light source is characterized in that it comprises a plurality of LEDs as the first lighting control element, said first lighting control element being chosen from the group consisting of a red-orange LED and a red-LED, and the light source comprises an additional plurality of LEDs as the at least one additional lighting control element, said at least one additional lighting control element being chosen from the group consisting of a blue LED, a green LED and an amber LED. LEDs are small lighting elements available in a great variety of emission colors. The spectral emission of the light source can be easily chosen by selection of the various colors emitted by the different LEDs and appropriate numbers thereof. The light source can be further characterized in that the light source comprises at least one further additional lighting control element consisting of at least one LED not selected from either the group of the first lighting control element or the additional lighting control element. By selecting more differently colored LEDs a broader coverage of the spectrum from 380-680 nm is attainable and thus an improvement of the CRI and/or color recognition is attainable. Alternatively, a light source is characterized in that the light source comprises a plurality of LEDs as the first lighting control element, said first lighting control element being chosen from the group consisting of a red-orange LED and a red-LED, and the light source comprises an additional plurality of LEDs as the at least one additional lighting control element, said at least one additional lighting control element being chosen from the group consisting of a cool white LED (CW) and a warm white LED. Alternatively this is also attainable with other whites, for example neutral white LEDs. 
     An alternative way to obtain a broader coverage of the spectrum is by using lighting control elements having an increased full width at half maximum (FWHM) of at least one significant emission peak in each of the first, second and third wavelength range. Significant in this respect means that measured spectral intensity at said peak are at least hundred times the level of the measured background noise signal. A minimal starting value of 12 nm for the FWHM is accepted, however, preferably the FWHM is at least 20 nm. Preferably the radiation should be emitted so as to be evenly distributed over the full ranges, without having any discernable peaks, as this would increase the color recognition possibilities. 
     An embodiment of the light source is characterized in that the light source is a low-pressure mercury vapor discharge lamp comprising a discharge vessel, the discharge vessel enclosing, in a gastight manner, a discharge space provided with an inert gas and mercury and comprising discharge means for maintaining a discharge in the discharge space, at least a part of a wall of the discharge vessel being provided with a luminescent layer comprising a mixture of a red emitting phosphor as the first lighting control element, and at least two phosphors chosen from a blue emitting phosphor, a green emitting phosphor, an amber emitting phosphor and a red-orange emitting phosphor as the one additional lighting control element and a further additional lighting control element. The blue phosphor preferably is BaMgAl 10 O 17 :Eu (BAM), Sr 5 (PO 4 ) 3 Cl:Eu (SCAP) and/or Sr 4 Al 14 O 25 :Eu (SAE), the green phosphor preferably is LaPO 4 :Ce,Tb (LAP), Sr 4 Al 14 O 25 :Eu and/or BaMg 2 Al 16 O 27 :Eu,Mn (BAM-green), the amber phosphor preferably is Sr 10 (PO 4 ) 6 F 2 :Sb (SHS), the red-orange phosphor preferably is Y 2 O 3 :Eu (YOX), and the red phosphor preferably is YVO 4 :Eu (YVO 4 ) and/or Mg 4 GeO 6 :Mn (MGM). These phosphors are cheap, well-known and widely applied in fluorescent lamps. Presently, a fluorescent lamp is a cheap alternative to a light source equipped with LEDs. 
     An embodiment of the light source is characterized in that the light source is a high pressure ceramic metal halide lamp as the lighting control element provided with an interference filter as the at least one additional lighting control element which at least partly, but not totally, reflects or absorbs light of a wavelength λ in the range of 380 nm≦λ≦600 nm and a cut-off wavelength in the range of 590-610 nm, so as to prevent, at least partly, the light in said range from reaching the surroundings of the light source, said interference filter preferably comprising alternating layers of Fe 2 O 3 /SiO 2  and SiO 2  provided on at least a part of an outer side of the lamp vessel. 
     General Electric Lighting Systems introduced two filters to be used together with High Pressure Sodium (=HPS) lamps to reduce the disturbing effect to sea turtles. Both were high-pass filters, with a cut-off at 530 nm (filter type #2422), or at 570 nm (filter type NLW). Below 520 or 560 nm, respectively, these filters completely blocked all light, reaching a transmittance of about 90% at 650 nm. Research has shown that the application of such filters together with an HPS lamp does not fully have the desired effect on sea turtles. The instant invention indicates that the cut-off wavelengths used in the lamps of GE are too short and should be at about 600 nm or somewhat higher to yield both the desired effect for sea turtles and safety effects for humans. Halogen lamps with similar filters were disclosed by GE in U.S. Pat. No. 5,578,892. However, the spectra emitted by these lamps are characterized by a value of P l  of only about 0.36. Besides that these lamps apparently did not have the required biological effect, a considerable amount of energy is emitted at wavelengths between 680 nm and 780 nm, where they contribute little to the human perception of light (intensity), making these lamps much less energy efficient than the light sources described here. To preferably fulfill the future requirements for energy efficiency, no more than 10% of the total emitted spectral power should be emitted between 680 nm and 780. To illustrate this boundary condition typical energy efficient lamps, like modern fluorescent lamps or LED lighting, fulfill this requirement, whereas typical incandescent or halogen lamps have much higher, inappropriate values. 
     The present invention provides a light source that predominantly emits light of predetermined, specific longer wavelengths that are hardly visible to, or at least hardly influencing the natural behavior of, short wavelength sensitive animals, such as both baby and adult sea turtles, insects, bats or rodents and other small mammals, yet still within the human visible spectrum and effective in illuminating outdoor living areas. However, to maintain a relatively simple and cheap construction of the light source and the luminaire, this spectrum preferably should be emitted by a single system, for example, having one mounting point, for example a socket, lamp post, mounting bracket, or standing foot, and one electrical power connection. The aim is to provide functional lighting, for example for working, reading, driving, inspecting, sports, etc., hence the use of the light source is less designed for lighting aimed at attaining an esthetical effect, such as decorative, festive, seasonal or architectural/city beautification lighting. The light source/luminaire should be designed or set to emit said type of spectrum, but it could also have the option to change to a different spectrum, e.g. by adding white light, or light in the short and medium wavelength ranges, or by dimming the light in the long wavelength range, in order to make the light more white for human safety when that takes priority over the ecological disturbance or if at a certain time or in a certain period the risk of this disturbance is absent (e.g. during hibernation of the affected species). 
     US2005/0168982 discloses a low pressure sodium discharge lamp, having a monochromatic line emission at 589 nm to protect wildlife. This lamp has the well-known disadvantages that it does not offer any color recognition, that it produces unpleasant light, and that it contributes to a relatively low extent to safety of humans during operation of the monochromatic light source; moreover, the emitted wavelength is too short to sufficiently limit the effects on the aforementioned animals. Therefore it has been generally proposed to mix its light with that of another source, indicating that color vision is possible in low pressure sodium vapor light mixed with other light. However, the necessary information as to which wavelengths to add and in what proportion to reach a sufficient level of color recognition with the smallest possible extra disturbance to the surrounding eco system, is never given. Also for some animals, e.g. for the Squirrel Treefrog ( Hyla squirella ) nocturnal color vision is important in mate choice and male-male competition. Obviously, it is at least questionable whether a standard low pressure sodium lamp would offer the desired level of color recognition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be explained in greater detail by means of the examples and the schematic drawings, in which 
         FIG. 1A  shows a cross-sectional view of a first embodiment of the light source according to the invention; 
         FIGS. 1B and 1C  show emission spectra built up by using respectively LEDs without phosphor conversion and phosphor-converted LEDs; 
         FIG. 2  shows a cross-sectional view of a second embodiment of the light source according to the invention; 
         FIG. 3A  shows a cross-sectional view of a third embodiment of the light source according to the invention; 
         FIG. 3B  shows transmission curves of a  5  layer and a 7 layer interference filter; 
         FIG. 3C  shows emission spectra of the lamp of  FIG. 3A  provided with one of the layers having one of the transmission curves shown in  FIG. 3B . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 1A  schematically shows a first embodiment of a light source  40  according to the invention. The light source comprises a plurality of LEDs comprising, as an example, one blue light-emitting diode (LED)  41 , twelve red LEDs  42  and two green LEDs  43 . In this embodiment, all LEDs are Luxeon™ I LEDs from Philips Lumileds Lighting Company™. In an alternative embodiment, different LEDs can be used, for example CREE XPE or XRE LEDs, or Luxeon Rebels. The LED  41 , the plurality of LEDs  42  and the plurality of LEDs  43  can preferably be dimmed in order to adjust the light output of the respective LEDs. The light source  40  has a light-transmissive exit window (not shown) facing the light emitting side of the LED, and a rear side (not shown) facing away from the light emitting side of the LED. The rear side preferably has a specular surface on the side facing the exit window. The light generated by the LEDs  41 ,  42 ,  43  is homogeneously mixed inside the light source  40  and emitted via the exit window. The emitted light has a color-rendering index R a  of about 30 and the parameter P l , being the ratio of the integral spectral power distribution over a first range of 600 nm≦λ≦680 nm to that of a total range of 380 nm≦λ≦680 nm, is 0.72. Tables 2-4 show alternative embodiments of the light source  40  in terms of the ratio of the number (#) of red, red-orange, amber, green and blue LEDs, the luminous flux of the light source, the color-rendering index R a  and the parameters P l , P m , and P s  of the light generated by the light source. The exact total number of LEDs in a light source  40  depends on the required light output and on the light output of the individual LEDs. Given the number of LEDs for each color in the light source  40 , one can calculate the lamp characteristics, for example spectral power distribution, luminous flux, efficacy, general color-rendering index R a  and parameter P l . Table 1 gives the properties of the various LEDs used in the calculations. When designing the light source  40 , a maximum value of the parameter P l  and a minimum value of the general color-rendering index R a  of the light generated by the light source  40 , are chosen. In addition, a minimum value of the power usage is chosen in order to balance the cost of the light source  40  relative to its light output. Given the spectral power distribution for each individual LED, the required number of specifically colored LEDs is determined via an iterative procedure.  FIG. 1B  shows a resulting spectral power distribution, i.e. the output power in W nm −1  versus the wavelength λ in nm of the generated light, which is built up using ‘direct’ LEDs, i.e. LEDs without phosphor conversion, with P L =82%. The light source has a ratio of 1:5:38 in the number of blue, green and red LEDs, as specified in Table 1. The light source emits light with a specific luminous flux of about 1870 lm. The general color-rendering index R a  is 44. The spectrum as generated by the light source has a spectral coverage for the first range of about 62%, a spectral coverage for the second range of practically 100%, and for the third range of about 40%.  FIG. 1C  shows a resulting spectral power distribution, i.e. the output power in W nm −1  versus the wavelength λ in nm of the generated light, which is built up using phosphor-converted LEDs, i.e. blue LEDs with a Y 3 Al 5 O 12 :Eu phosphor (=YAG), with P L =81%. The light source has a ratio of 4:18 in the number of warm-white and red-orange LEDs, as shown in Table 5. The light source emits light with a specific luminous flux of about 1000 lm. The general color-rendering index R a  is 76. The spectrum as generated by the light source has a spectral coverage for the first range of about 67%, a spectral coverage for the second range of practically 100%, and for the third range of about 57%. Wavelengths above 680 nm hardly contribute to the color rendering index Ra and hence spectral coverage at longer wavelengths than 680 nm is considered irrelevant in this case. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Properties of LEDs used in calculations and experiments 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Optical power 
                 Peak wavelength 
                 FWHM 
               
               
                   
                 Color 
                 [W] 
                 [nm] 
                 [nm] 
               
               
                   
                   
               
               
                   
                 Blue 
                 0.387 
                 475 
                 24 
               
               
                   
                 Green 
                 0.107 
                 545 
                 22 
               
               
                   
                 Amber 
                 0.056 
                 588 
                 26 
               
               
                   
                 Red-Orange 
                 0.118 
                 615 
                 24 
               
               
                   
                 Red 
                 0.159 
                 625 
                 24 
               
               
                   
                 Cool white 
                 0.333 
                 CCT 6500K 
                 — 
               
               
                   
                 Warm white 
                 0.223 (74 lm) 
                 CCT 3800K 
                 — 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Embodiments with 0.65 &lt; P 1  &lt; 0.70 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                 red- 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Blue 
                 Green 
                 Amber 
                 orange 
                 red 
                 Flux 
                 CRI 
                 lm/led 
                 P s   
                 P m   
                 P l   
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 0.5 
                 2.5 
                 4 
                 8 
                 7 
                 900 
                 80 
                 40.9 
                 0.07 
                 0.25 
                 0.68 
               
               
                 1 
                 1 
                 4 
                 8 
                 8 
                 855 
                 70 
                 38.9 
                 0.13 
                 0.18 
                 0.68 
               
               
                 0.5 
                 1.5 
                 6 
                 6 
                 8 
                 855 
                 82 
                 38.9 
                 0.07 
                 0.24 
                 0.68 
               
               
                 1 
                 0 
                 6 
                 6 
                 9 
                 810 
                 55 
                 36.8 
                 0.13 
                 0.18 
                 0.69 
               
               
                 0.5 
                 3.5 
                 0 
                 13 
                 5 
                 964 
                 71 
                 43.8 
                 0.07 
                 0.23 
                 0.70 
               
               
                 1 
                 1 
                 11 
                 31 
                 0 
                 1665 
                 47 
                 37.8 
                 0.08 
                 0.27 
                 0.65 
               
               
                 0.5 
                 2.5 
                 0 
                 19 
                 0 
                 937 
                 77 
                 42.6 
                 0.07 
                 0.24 
                 0.69 
               
               
                 0.5 
                 1 
                 6 
                 6 
                 8.5 
                 841 
                 77 
                 38.2 
                 0.07 
                 0.22 
                 0.70 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Embodiments with 0.70 &lt; P 1  &lt; 0.80 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                 red- 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Blue 
                 Green 
                 Amber 
                 orange 
                 red 
                 Flux 
                 CRI 
                 lm/led 
                 P s   
                 P m   
                 P l   
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 0.5 
                 2.5 
                 2 
                 10 
                 7 
                 919 
                 77 
                 41.7 
                 0.07 
                 0.22 
                 0.71 
               
               
                 1 
                 2 
                 2 
                 1 
                 16 
                 901 
                 54 
                 41.0 
                 0.11 
                 0.14 
                 0.74 
               
               
                 0.5 
                 2.5 
                 1 
                 13 
                 5 
                 928 
                 77 
                 42.2 
                 0.07 
                 0.22 
                 0.71 
               
               
                 0.5 
                 2.5 
                 1 
                 13 
                 6 
                 967 
                 77 
                 42.0 
                 0.07 
                 0.21 
                 0.73 
               
               
                 1 
                 1 
                 12 
                 12 
                 18 
                 1656 
                 66 
                 37.6 
                 0.07 
                 0.20 
                 0.72 
               
               
                 1 
                 1 
                 11 
                 16 
                 15 
                 1665 
                 63 
                 37.8 
                 0.07 
                 0.21 
                 0.72 
               
               
                 0.5 
                 2.5 
                 0 
                 13 
                 6 
                 937 
                 75 
                 42.6 
                 0.07 
                 0.19 
                 0.74 
               
               
                 1 
                 0 
                 3 
                 3 
                 15 
                 838 
                 49 
                 39.9 
                 0.12 
                 0.10 
                 0.78 
               
               
                 1 
                 1 
                 1 
                 1 
                 18 
                 883 
                 59 
                 40.1 
                 0.11 
                 0.09 
                 0.79 
               
               
                 1 
                 1 
                 1 
                 1 
                 19 
                 923 
                 60 
                 40.1 
                 0.10 
                 0.09 
                 0.80 
               
               
                 1 
                 4 
                 5 
                 40 
                 20 
                 2835 
                 71 
                 40.5 
                 0.04 
                 0.18 
                 0.77 
               
               
                 1 
                 4 
                 5 
                 47 
                 20 
                 3113 
                 67 
                 40.4 
                 0.04 
                 0.18 
                 0.78 
               
               
                 1 
                 4 
                 5 
                 55 
                 22 
                 3511 
                 63 
                 40.3 
                 0.04 
                 0.18 
                 0.79 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Embodiments with 0.80 &lt; P 1  &lt; 0.95 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                 red- 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Blue 
                 Green 
                 Amber 
                 orange 
                 red 
                 Flux 
                 CRI 
                 lm/led 
                 P s   
                 P m   
                 P l   
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 1 
                 1 
                 1 
                 20 
                 963 
                 62 
                 40.1 
                 0.10 
                 0.09 
                 0.81 
               
               
                 1 
                 4 
                 5 
                 62 
                 26 
                 3948 
                 59 
                 40.3 
                 0.03 
                 0.17 
                 0.80 
               
               
                 1 
                 4 
                 5 
                 72 
                 30 
                 4505 
                 54 
                 40.2 
                 0.03 
                 0.16 
                 0.81 
               
               
                 1 
                 4 
                 0 
                 4 
                 55 
                 2644 
                 69 
                 41.3 
                 0.04 
                 0.10 
                 0.86 
               
               
                 1 
                 4 
                 0 
                 4 
                 80 
                 3639 
                 67 
                 40.9 
                 0.03 
                 0.08 
                 0.89 
               
               
                 1 
                 2 
                 0 
                 25 
                 75 
                 4142 
                 43 
                 40.2 
                 0.03 
                 0.09 
                 0.89 
               
               
                   
               
            
           
         
       
     
     Alternatively, a combination of long wavelength radiating LEDs and white (phosphor converted) LEDs can be used, e.g. CW and WW LEDs listed in table 1. Calculations including phosphor converted LEDs are given in Table 5. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Embodiments using direct and phosphor converted LEDs. 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 red- 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                   
                 or- 
                   
                   
                   
                   
                   
                 lm/ 
               
               
                 Blue 
                 ange 
                 red 
                 cw 
                 ww 
                 Flux 
                 CRI 
                 led 
                 P s   
                 P m   
                 P l   
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 20 
                   
                 2 
                   
                 996 
                 72.6 
                 45.25 
                 0.09 
                 0.23 
                 0.67 
               
               
                   
                   
                 19 
                 3 
                   
                 898 
                 48.2 
                 40.8 
                 0.10 
                 0.15 
                 0.74 
               
               
                   
                 18 
                   
                   
                 4 
                 1011 
                 76 
                 45.95 
                 0.06 
                 0.25 
                 0.68 
               
               
                   
                 19 
                   
                   
                 3 
                 977 
                 67.7 
                 44.4 
                 0.05 
                 0.23 
                 0.71 
               
               
                   
                   
                 20 
                 2 
                   
                 829 
                 57.2 
                 37.67 
                 0.07 
                 0.12 
                 0.80 
               
               
                   
                   
                 18 
                   
                 4 
                 861 
                 59.5 
                 39.12 
                 0.05 
                 0.14 
                 0.80 
               
               
                   
                 20 
                   
                   
                 2 
                 943 
                 53.7 
                 42.85 
                 0.03 
                 0.21 
                 0.75 
               
               
                   
                 21 
                   
                   
                 1 
                 909 
                 32.4 
                 41.31 
                 0.02 
                 0.19 
                 0.79 
               
               
                   
                 21 
                   
                   
                 2 
                 983 
                 52 
                 42.72 
                 0.03 
                 0.21 
                 0.75 
               
               
                   
                 21 
                   
                 1 
                   
                 935 
                 49.5 
                 42.51 
                 0.05 
                 0.20 
                 0.75 
               
               
                 1 
                 120 
                   
                 1 
                   
                 4901 
                 17.4 
                 40.18 
                 0.04 
                 0.17 
                 0.79 
               
               
                   
                   
                 25 
                   
                 1 
                 1069 
                 42.6 
                 41.1 
                 0.01 
                 0.07 
                 0.91 
               
               
                   
                   
                 20 
                   
                 2 
                 943 
                 67.6 
                 42.9 
                 0.02 
                 0.10 
                 0.87 
               
               
                   
               
            
           
         
       
     
     The light source then comprises a plurality of LEDs as the first lighting control element, said first lighting control element being chosen from the group consisting of a red-orange LED and a red-LED, and the light source comprises an additional plurality of LEDs as the at least one additional lighting control element, said at least one additional lighting control element being chosen from the group consisting of a cool white LED (CW) and a warm white LED (WW). 
     In  FIG. 2  a portion of a second embodiment of the light source according to the invention is shown and comprises a low pressure mercury discharge lamp as the lighting control element provided with a phosphor layer as the at least one additional lighting control element.  FIG. 2  only shows one end portion of the light source  10  actually; the light source  10  comprises two mutually opposite, identical end portions, each sealing one end of an elongated discharge vessel  12 . The light sources  10  are low-pressure gas discharge lamps comprising a light-transmitting discharge vessel  12  which encloses a discharge space  14  in a gastight manner. The discharge space  14  comprises a gas filling of mercury and a buffer gas, for example, argon or xenon. The low-pressure gas discharge lamp  10  further comprises discharge means  18  for maintaining a discharge in the discharge space  14 . The discharge means  18  couple energy into the discharge space  14 , for example, via capacitive coupling, inductive coupling, microwave coupling, or via electrodes. Electrons and ions in the gas filling of the discharge space  14  collide with the mercury compound in the gas filling. Due to the collision, the mercury atoms are excited and subsequently emit light, mainly ultraviolet light at a wavelength of approximately 254 nm. The low-pressure gas discharge lamp  10  comprises a luminescent layer  16  of a luminescent material which absorbs ultraviolet light and subsequently converts the absorbed ultraviolet light into visible light. 
     The appropriate spectra for the lamp according to the invention can be arrived at by a fluorescent lamp, using an appropriate combination of phosphors in the luminescent layer. Given the amount of phosphor material in weight % for each phosphor emitting a specific color in the light source  10 , one can calculate the lamp characteristics, for example spectral power distribution, luminous flux, efficacy, general color-rendering index R a  and parameter P l . When designing the light source  10 , a maximum value of the parameter P l  and a minimum value of the general color-rendering index R a  of the light generated by the light source  10 , are chosen. Possible combinations of phosphors are given in table 6. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Examples of combinations of phosphors for low pressure mercury discharge lamps (= fluorescent lamps). 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                   
                   
                 red- 
                   
                   
                   
                   
                   
               
               
                   
                 blue 
                   
                 green 
                   
                 amber 
                   
                 orange 
                   
                 red 
               
               
                   
                 [wght 
                   
                 [wght 
                   
                 [wght 
                   
                 [wght 
                   
                 [wght 
               
               
                 color 
                 ratio] 
                 [% wght] 
                 ratio] 
                 [% wght] 
                 ratio] 
                 [% wght] 
                 ratio] 
                 [% wght] 
                 ratio] 
                 [% wght] 
                 Flux 
                 CRI 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 phosphor 
                 BAM 
                   
                 LAP 
                   
                   
                   
                 YOX 
                   
                   
                   
                   
                   
               
               
                 ratio 
                 3 
                 1.55 
                 8.5 
                 4.39 
                   
                   
                 182 
                 94.06 
                   
                   
                  455k 
                 72 
               
               
                 ratio 
                 3 
                 0.61 
                 14   
                 2.85 
                   
                   
                 475 
                 96.54 
                   
                   
                  905k 
                 76 
               
               
                 ratio 
                 3 
                 0.36 
                 8.5 
                 1.02 
                   
                   
                 825 
                 98.63 
                   
                   
                 1384k 
                 62 
               
               
                 ratio 
                 3 
                 0.03 
                 8.5 
                 0.09 
                   
                   
                 9120 
                 99.87 
                   
                   
                 1915k 
                 41 
               
               
                 phosphor 
                 BAM 
                   
                 BAM-green 
                   
                   
                   
                 YOX 
               
               
                 ratio 
                 2.9 
                 0.57 
                 8.4 
                 1.66 
                   
                   
                 494 
                 97.76 
                   
                   
                 1190k 
                 57 
               
               
                 ratio 
                 2.9 
                 0.36 
                 8.4 
                 1.05 
                   
                   
                 787 
                 98.58 
                   
                   
                 1800k 
                 66 
               
               
                 ratio 
                 2.9 
                 0.17 
                 8.4 
                 0.50 
                   
                   
                 1670 
                 99.33 
                   
                   
                 36500k  
                 64 
               
               
                 ratio 
                 2.9 
                 0.05 
                 8.4 
                 0.15 
                   
                   
                 5700 
                 99.80 
                   
                   
                 119312k  
                 40 
               
               
                 phosphor 
                 BAM 
                   
                 SAE 
                   
                   
                   
                 YOX 
               
               
                 ratio 
                 2.9 
                 0.55 
                 8.4 
                 1.58 
                   
                   
                 520 
                 97.87 
                   
                   
                 1272k 
                 53 
               
               
                 ratio 
                 2.9 
                 0.34 
                 8.4 
                 0.99 
                   
                   
                 836 
                 98.67 
                   
                   
                 1931k 
                 64 
               
               
                 ratio 
                 2.9 
                 0.16 
                 8.4 
                 0.48 
                   
                   
                 1750 
                 99.36 
                   
                   
                 3837k 
                 64 
               
               
                 ratio 
                 2.9 
                 0.00 
                 8.4 
                 0.01 
                   
                   
                 64500 
                 99.98 
                   
                   
                 135227k  
                 40 
               
               
                 phosphor 
                 SCAP 
                   
                 LAP 
                   
                   
                   
                 YOX 
               
               
                 ratio 
                 2.9 
                 1.26 
                 8.4 
                 3.66 
                   
                   
                 218 
                 95.07 
                   
                   
                  556k 
                 71 
               
               
                 ratio 
                 2.9 
                 0.80 
                 8.4 
                 2.32 
                   
                   
                 350 
                 96.87 
                   
                   
                  831k 
                 74 
               
               
                 ratio 
                 2.9 
                 0.39 
                 8.4 
                 1.12 
                   
                   
                 741 
                 98.50 
                   
                   
                 1649k 
                 66 
               
               
                 ratio 
                 2.9 
                 0.01 
                 8.4 
                 0.04 
                   
                   
                 22800 
                 99.95 
                   
                   
                 47763k  
                 41 
               
               
                 phosphor 
                 SCAP 
                   
                 LAP 
                   
                   
                   
                   
                   
                 MGM 
               
               
                 ratio 
                 5.8 
                 4.52 
                 19.6 
                 15.26 
                   
                   
                   
                   
                 103 
                 80.22 
                  398k 
                 −10 
               
               
                 ratio 
                 2.9 
                 3.70 
                 8.4 
                 10.73 
                   
                   
                   
                   
                 67 
                 85.57 
                  216k 
                 −41 
               
               
                 ratio 
                 2.9 
                 2.67 
                 8.4 
                 7.73 
                   
                   
                   
                   
                 97.3 
                 89.59 
                  269k 
                 −65 
               
               
                 ratio 
                 2.9 
                 1.64 
                 8.4 
                 4.76 
                   
                   
                   
                   
                 165 
                 93.59 
                  387k 
                 −77 
               
               
                 ratio 
                 2.9 
                 0.68 
                 8.4 
                 1.96 
                   
                   
                   
                   
                 418 
                 97.37 
                  827k 
                 −41 
               
               
                 phosphor 
                 BAM 
                   
                 LAP 
                   
                   
                   
                   
                   
                 YVO4 
               
               
                 ratio 
                 2.9 
                 1.77 
                 8.4 
                 5.11 
                   
                   
                   
                   
                 153 
                 93.12 
                  384k 
                 59.8 
               
               
                 ratio 
                 2.9 
                 1.12 
                 8.4 
                 3.25 
                   
                   
                   
                   
                 247 
                 95.63 
                  575k 
                 66.8 
               
               
                 ratio 
                 2.9 
                 0.53 
                 8.4 
                 1.55 
                   
                   
                   
                   
                 532 
                 97.92 
                 1154k 
                 67 
               
               
                 phosphor 
                 BAM 
                   
                 LAP 
                   
                 SHS 
                   
                 YOX 
               
               
                 ratio 
                 2.9 
                 0.71 
                 8.4 
                 2.06 
                 2.8 
                 0.69 
                 393 
                 96.54 
                   
                   
                 1034k 
                 72 
               
               
                 ratio 
                 2.9 
                 0.34 
                 8.4 
                 0.99 
                 2.8 
                 0.33 
                 835 
                 98.34 
                   
                   
                 1539k 
                 75 
               
               
                 ratio 
                 2.9 
                 0.14 
                 8.4 
                 0.40 
                 5.6 
                 0.26 
                 2100 
                 99.20 
                   
                   
                 4741k 
                 67 
               
               
                 ratio 
                 2.9 
                 0.01 
                 8.4 
                 0.02 
                 2.8 
                 0.01 
                 38000 
                 99.96 
                   
                   
                 79650k  
                 40.7 
               
               
                   
               
            
           
         
       
     
     In  FIG. 3A  a third embodiment of the light source according to the invention comprises a high pressure sodium lamp, in this case a Philips 70 W color \828 CDO lamp as the lighting control element. The (HPS-) lamp comprises a pair of electrodes  22  arranged inside a lamp vessel  21  made of ceramic material, for example made of translucent, gastight alumina (TGA), the lamp vessel is enveloped by a hard glass outer bulb  24  provided with a lamp base  27 . The (outer) surface  26  of the lamp vessel  21  is provided with an interference filter  25  as the at least one additional lighting control element, and comprises alternating layers of Fe 2 O 3 /SiO 2  and SiO 2 , starting with a layer of Fe 2 O 3 /SiO 2 , on the glass surface of the outer bulb  24 . The lamp shown in  FIG. 3A  is provided via dip-coating with a 5-layer or, for example with a 7-layer interference filter. Possible compositions of the filter are shown in Table 3 and Table 4, and the transmission spectrum of both the 5-layer filter and the 7-layer filter are shown in  FIG. 3B . Both said filters have a relatively high reflectance (low transmission) for light with a wavelength λ in the range of 380 nm≦λ≦600 nm, their cut-off wavelength being approximately 600 nm. Very suitable filters have a cut-off wavelength in the range of 590 to 610 nm. Apparently the 7-layer filter is somewhat more transparent in the wavelength range 380 nm≦λ≦600 nm than the 5-layer filter. 
                     TABLE 3                  Composition of the 5 layer interference filter                                     Refractive   Physical       Layer   Material   Index [—]   Thickness (nm)                     Air                                     1   Fe 2 O 3 /SiO 2     2.719   34.39       2   SiO 2     1.462   276.6       3   Fe 2 O 3 /SiO 2     2.719   67.34       4   SiO 2     1.462   264.1       5   Fe 2 O 3 /SiO 2     2.719   45.03       Substrate:       1.462       quartz glass                    
The composition of the alternative 7-layer interference filter is shown in Table 4.
 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Composition of the 7 layer interference filter 
               
            
           
           
               
               
               
               
            
               
                   
                   
                 Refractive 
                 Physical 
               
               
                 Layer 
                 Material 
                 Index [—] 
                 Thickness (nm) 
               
            
           
           
               
               
            
               
                 Air 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 1 
                 Fe 2 O 3 /SiO 2   
                 2.712 
                 30.09 
               
               
                 2 
                 SiO 2   
                 1.462 
                 285.97 
               
               
                 3 
                 Fe 2 O 3 /SiO 2   
                 2.712 
                 58.42 
               
               
                 4 
                 SiO 2   
                 1.462 
                 263.1 
               
               
                 5 
                 Fe 2 O 3 /SiO 2   
                 2.712 
                 62.28 
               
               
                 6 
                 SiO 2   
                 1.462 
                 286.54 
               
               
                 7 
                 Fe 2 O 3 /SiO 2   
                 2.712 
                 30.9 
               
               
                 Substrate: 
                   
                 1.462 
               
               
                 quartz glass 
               
               
                   
               
            
           
         
       
     
       FIG. 3C  shows the emission spectrum of the high pressure sodium lamp of  FIG. 3A  in combination with the 7-layer interference filter. Table 5 shows a summary of the spectral characteristics of the emission spectrum shown in  FIG. 3C . 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Characteristics of the emission spectra of the lamps of FIGS. 3C-3E. 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 Filter 
                   
                 Power 
                 Power 
                 Power 
                 Coverage 
                 Coverage 
                 Coverage 
               
               
                 Lamp type 
                 layers 
                 Ra 
                 short 
                 medium 
                 long 
                 short 
                 medium 
                 long 
               
               
                   
               
               
                 70 W CDO\828 
                 7 
                 50 
                 2.0% 
                 3.6% 
                 94.4% 
                 34.4% 
                 44.7% 
                 100.0% 
               
               
                   
               
            
           
         
       
     
     In alternative embodiments, the interference filter is positioned at the inner or outer surface of the hard glass outer bulb  24 . In other alternative embodiments, the interference filter is arranged at a position remote from the light source, for example on a transparent shroud around the light source, on the front glass of a light fixture or in between the light source and the front glass of a light fixture. 
     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 “comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. 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. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.