Patent Description:
In addition to its use in sight, light powerfully regulates the so-called biological, non-visual (or non-image forming, NIF) responses of humans and other mammals. In particular, the human eye comprises a receptor located in the retina that is based on the photopigment melanopsin (the "melanopsin receptor"). The melanopsin phototpigment has, for humans, a peak wavelength sensitivity for the blue portion of the visible spectrum. The human eye contains a sensory system that comprises several other photopigments (rods and cones) next to melanopsin. The light impinging on these receptors regulates the circadian system of humans and other mammals, as well as the acute effects of light (e.g. an increased alertness and melatonin suppression). Melatonin is a hormone that varies in a daily cycle, allowing the chronobiological entrainment of the circadian rhythm of several biological functions.

European patent application publication number <CIT> discloses a method of controlling a lamp to support circadian rhythm. The light is emitted with a spectral composition and intensity that is a function of the time of day between sunrise and sunset.

<CIT> relates to a lighting device for generating a wake-up stimulus and discloses a lighting device comprising one or more light sources arranged to generate light, an accommodating device having an external boundary which is at least partly translucent and is arranged to accommodate the one or more light sources and a controller. The lighting device can generate two types of light. One or more lighting parameters selected from the group consisting of the first luminous intensity of the first type of light, the second luminous intensity of the second type of light, the color point of the first type of light and the color point of the second type of light can be controlled. This allows task lighting and atmosphere lighting. The document also discloses a method of providing a wake-up stimulus by means of such a lighting device.

<CIT> relates to a lighting system for stimulating a user's energy by emitting bluish wake-up light and tuning the bluish light towards a daytime-like white light.

It is an object of the following to provide a lighting system, an apparatus comprising the lighting system and a method of controlling a light source.

According to a first aspect there is provided a lighting system for illuminating a space, the lighting system comprising: at least one light source; and at least one controller configured to: receive an indication of a pre-selected duration of an emission period for which the at least one light source is to emit light, control the at least one light source to emit light for the duration of the emission period, select a first spectrum in
dependence on the duration of the emission period, and control the at least one light source to emit the light with the first spectrum during at least part of the emission period.

The at least one controller may be configured to control the lighting system to select the first spectrum in further dependence on an intensity of the light to be emitted during the emission period and/or the time of day during which the emission period lies.

The at least one controller may be configured to control the lighting system to select the first spectrum in further dependence on: an intensity and/or spectrum from one or more other sources illuminating an area adjacent to the space illuminated by the lighting system, and/or a duration of the light emitted from the one or more other sources and/or the state of the circadian clock of a user within said space during the emission period.

The at least one controller is configured to select a first spectrum in dependence on the duration of the emission period by selecting spectral components of light to be emitted and intensities thereof.

The intensity of the light emitted during the emission period may be pre-selected prior to the determination of the first spectrum, the first spectrum being selected in response to the pre-selected intensity.

The duration of the emission period is pre-selected. The duration of the emission period and/or the intensity of the light to be emitted during the emission period may be pre-selected by a user.

The emission period may be pre-selected from a range between <NUM> seconds and <NUM> hours.

The intensity of the first spectrum may be less than <NUM>-lux and, in dependence on this intensity, the at least one controller may be configured to include a spectral component having a wavelength of <NUM>.

The at least one controller may be configured to generate the first spectrum in dependence on whether the light is to be emitted continuously or discontinuously during the emission period. The light may be emitted discontinuously in pulses of <NUM> minutes and the spectral composition of light is matched to an m-cone absorption spectrum.

The at least one controller may be configured to generate the light so as to suppress spectral components responsible for melatonin suppression in humans.

The at least one controller may be operable to set a start and/or end point of the emission period.

There is also provided a display apparatus comprising a lighting system as described in any of the above.

There is also provided a method of controlling at least one light source, the method comprising: receiving an indication of a pre-selected duration of an emission period for which the at least one light source is to emit light, controlling the at least one light source to emit light for the duration of the emission period, selecting a first spectrum in dependence on the duration of the emission period, and controlling the at least one light source to emit the light with the first spectrum during at least part of the emission period.

There is further provided computer program product embodied on at least one computer-readable storage medium and configured so as when executed on one or more processors of a lighting system to perform operations of: receiving an indication of a pre-selected duration of an emission period for which the at least one light source is to emit light, controlling at least one light source to emit light for at least the duration of the emission period, selecting a first spectrum in dependence on the duration of the emission period, and controlling the at least one light source to emit the light with the first spectrum during at least part of the emission period.

These and other aspects are apparent from and will be elucidated with reference to the embodiments described hereinafter.

Items having the same reference numbers in different figures have the same functional features. If the function of such an item has been explained, there is no necessity for repeated explanation thereof in the detailed description as the skilled person is already considered to be enabled.

Non-visual responses to light are mediated by retinal transduction pathways that have a non-constant reaction to impinging light. Instead, the response of the retinal transduction pathways varies with the intensity and duration of the light exposure. Therefore the action spectrum for these responses is not fixed. By exploiting this effect, a lighting system located in an area can be configured to engender a targeted biological reaction in a user located in that area.

In particular, the following discloses a system in which the composition of a light spectrum (which can comprise at least one of the selection of spectral components and the intensity of each spectral component) produced by a lighting system can be adapted in dependence on the exposure duration used or set. In embodiments, the system allows a user (e.g. an end-user or a designer of the system) to pre-select a predetermined time program for controlling the lighting for some other reason than its photo-biological effect. For example, the user may set a certain wake-up light scheduled to come on around the time the user plans to wake up (e.g. the light may be programmed to come on once with a continuous emission or in pulses of a few minutes to gradually wake up the user). Depending on the duration of the exposure that the user has set, the system will then automatically adapt the spectrum of this light to additionally provide a more optimal photo-biological effect such as suppressing the secretion of the hormone melatonin.

In another example, the user triggers the lights to turn on or dim up, either explicitly by activating an explicit user control, or by triggering a presence sensor which in turn triggers the lights when the user is detected to be present. If the user leaves the lights on or dimmed up for longer than a certain threshold duration of time, or remains present so that the presence sensor continues to keep the lights on or dimmed up for longer that a certain threshold duration of time, the system may adapt the spectrum of the light to produce a more optimal photo-biological effect given the length of time the lights have been on or dimmed up.

Further, in embodiments the system may also allow a user to select the intensity of the light emitted by the lighting system, and a combination of the exposure duration and the selected intensity of light to be emitted may influence the selection of a composition of a light spectrum to be emitted by a lighting system.

Current lighting systems do not adapt the composition and/or the intensity of a light spectrum produced by a lighting system in dependence on the exposure duration used or set (N. in <CIT> the spectrum is a function of time of day but does not depend on the exposure duration).

<FIG> schematically shows a block diagram of a lighting system. The lighting system comprises at least one light source <NUM> and at least one controller <NUM> that drives the light source <NUM> to emit light with a varying spectrum. For example the light source <NUM> may comprise a plurality of lighting elements such as LEDs which emit different colours, allowing the spectrum to be controlled by turning the different coloured elements (e.g. LEDs) on and off in different combinations, and/or controlling their relative intensities.

The controller <NUM> comprises a driver which receives an input voltage and supplies a current and/or voltage DS to the light source <NUM>. The driver receives the AC mains voltage Vm and has an electronic circuit for controlling the current through or the voltage across the light source <NUM>. The controller <NUM> is thus able to control when the light source <NUM> turns on and off, and/or the intensity with which it emits light when on. The controller <NUM> is also able to control the spectrum with which the light source <NUM> emits light when on. For example if the light source <NUM> comprises different coloured LEDs, the spectrum of the combined light can be varied by changing the ratio of currents through or voltages across the LEDs. Usually, LEDs are current driven. In other examples, circuits that vary the spectrum of a single lamp by, for example, changing the frequency of duty-cycle of the current through or the duration across the single lamp, can be used to control the spectrum of combined light from multiple lamps.

The controller <NUM> also comprises control functionality for controlling the timing with which the light source <NUM> is turned on and off and/or varies its intensity, and also for selecting the spectrum with which the light source <NUM> emits (via the driver circuitry discussed above). The control functionality may be implemented in software stored in one or more storage media of the system, and arranged for execution on one or more processors of the system; or alternatively the control functionality may be implemented in dedicated hardware circuitry, or configurable or reconfigurable circuitry such as a pin grid array or Field Programmable Gate Array; or any combination of such software and circuitry.

The control functionality of the controller <NUM> comprises a timer (implemented in hardware or software) arranged to control the light source <NUM> to emit for a first, defined period of time, an emission period, and also to control the spectrum (intensity and/or components thereof) with which the light source <NUM> emits its light during the emission period in dependence on a pre-selected duration of the emission period.

Where it is said the (at least one) light source <NUM> is controlled to emit during an emission period, this may mean either turning the light source <NUM> on or dimming it up, having been turned off or dimmed down immediately prior to the emission period and also being turned off or dimmed down immediately following the emission period. The light source may be controlled to emit continuously during the emission period, or the light source may be controlled to emit light in a train of light pulses during the emission period. The light source <NUM> may be controlled to emit with a single, constant spectrum of light during the emission period, or may be controlled to emit such that the spectrum of light varies during the emission period. In the case of a train of pulses, the light source may be controlled to emit no light between each light pulse in the train, or emit at a dimmed-down level. The light pulses may have the same spectrum as each other or a different spectrum to each other. Examples of these various embodiments are described below.

The controller may control the light source <NUM> to emit light having the selected spectrum during the entire emission period. Alternatively, the controller may control the light source <NUM> to emit light having a selected spectrum for just a part of the emission period (e.g. a later part). For example, where the controller receives an advance notification that light will be emitted for at least <NUM> minutes, the controller <NUM> determines in advance that the spectrum is to be varied after, for example, <NUM> minutes to engender a particular NIF response using certain receptors.

In the case where the spectrum varies within the emission period, the controller may determine to periodically or aperiodically vary the spectrum in that emission period so as to cause a pulsing colour light to be emitted from the light source <NUM> (alternatively or in addition to pulses in intensity, e.g. on-off pulses). During that emission period, there may or may not be instances in which no light is being emitted. For example, where the spectrum is to be varied, the light source <NUM> may be controlled to emit no light before emitting the changed spectrum.

It is noted that the control functionality of the controller may be configured to provide a static and/or a time-varying control of a light source in dependence on the duration for which the light source emits light over an emission period. Either way, the static spectrum or time-varying profile of the spectrum is determined in advance based on knowledge of a pre-selected (e.g. user-selected) duration for which the light source is going to emit light. This control may involve selecting at least a first spectrum (including spectral components and (optionally) individually selecting intensities of the spectral components) in dependence on the duration of the emission period.

In embodiments the timer (implemented in hardware or software) may also be operable to set the starting instant and/or end instant of the emission period mentioned above. The controller may comprise an input for receiving a command setting the duration of the emission period, or indicating that an emission period of a selected duration should begin. The command may be a user command, which may be input to the controller via a user interface.

In one example, the controller <NUM> is configured to control the at least one light source <NUM> to emit light according to a predetermined time program defining at least the duration of the emission period, and optionally the start and/or end points of the emission period, and/or times or durations of other periods when the light source is on or off or dimmed up or down. For example, said schedule may further define an off period immediately prior to and/or after the emission period, during which the at least one controller turns off the at least one light source. The controller <NUM> may be arranged to receive an indication of the time schedule including at least the duration of the emission period (and any other timing of the light source) from a user via a user interface to which the controller <NUM> is connected. For instance the time schedule may set the timing of a wake-up light, or a daily light profile in an environment such as a school, hospital or elderly care institution. In such cases, the user has set the time schedule of the lighting for some other reason such as to provide a wake-up light in the morning or prior to work, or to save energy by only turning on the lights at certain times. The controller <NUM> additionally adapts the spectrum of the light to provide a more appropriate biological response given the timing that the user has selected (e.g. enhancing or reducing stimulation of melanopsin, or other photopigments, as a result of the light exposure).

In another example the controller <NUM> is configured to trigger the start of the emission period ("on" period) in response to an event, and to dynamically adapt the spectrum in response to how long the lights stay on. For example, the controller <NUM> may receive a user input via an explicit user control indicating that the light source <NUM> is to be turned on or dimmed up, and in response the first timer period also starts running. If the controller <NUM> does not receive a complementary user input to turn off or dim down the light source <NUM> before a certain time has elapsed, such that the emission period has exceeded a certain threshold, then the controller <NUM> adapts the spectrum of the light to produce a more appropriate biological effect given the length of time the lights have been on so far (e. g to enhance or reduce stimulation of melanopsin, or other photopigments, as a result of the light exposure). In a similar example, the controller <NUM> is connected to a presence sensor which can detect the presence of a user. The controller <NUM> automatically turns on or dims up the light source <NUM> when it detects the user presence or user action, and automatically turns off or dims down the light source <NUM> if no user presence is detected. In this case, the controller <NUM> can also begin timing the emission period when presence is detected (and so when the lights are turned on or dimmed up). If the user is detected to remain present for longer than a certain time, such that the lights have remained on and the emission period has exceeded a certain threshold, the controller <NUM> again adapts the spectrum of the light output accordingly.

In further embodiments, the controller <NUM> may be further configured to control the lighting system to generate the first spectrum of light during the emission period in dependence on at least one of: a preselected intensity of the first spectrum of light, a light source emission in the immediate vicinity of the lighting system, a light exposure duration in the immediate vicinity of the lighting system during a time period immediately prior to the emission period and/or the time of day in the immediate locality of the light source controlled by the lighting system. Immediate vicinity here means the light from another source encroaches on the space illuminated by the lighting system and/or falls in a region immediately outside of the space illuminated by the lighting system. For an example of the latter case, one may consider how a light in a previous room (such as a corridor) affects the user's response to new light in a new room when selecting a spectrum for the new light.

In yet further embodiments, the controller <NUM> may be further configured to control the light source <NUM> to generate a spectrum selected for the emission period in further dependence on whether the emitted light is pulsed or continuous during the emission period.

The following presents information on the retinal-transduction pathways.

Under normal conditions, light is the main stimulus that influences the circadian system. Melanopsin receptors (i.e. melanopsin containing retinal ganglion cells (RGCs - nerve cells whose body is outside the central nervous system)) play an important role in mediating this influence via so-called biological, nonvisual responses to light. The melanopsin action spectrum in humans shows a peak sensitivity at about <NUM>-<NUM>.

The retinal-transduction pathway response to impinging light depends on the time of day, circadian phase, light history and the intensity and duration of the light exposure. Various photoreceptors, including rods, cones and melanopsin receptors, contribute to signal formation to the suprachiasmatic nucleus (SCN) (the SCN plays a role in the brain in the circadian rhythm) that results from a complex interplay between these different retinal photoreceptors.

The pupil response is under the control of both the cones and the melanopsin (third receptor). This is illustrated in <FIG>, which demonstrates the relative influence of cones and melanopsin receptors on pupil size (y-axis) as a function of logarithmic irradiance (in photons/cm<NUM>/s) along the x-axis. As the pulse durations increase (i.e. as the cumulative irradiance doses increases), the melanopsin receptors have a much greater influence on the pupil size than the cone receptors. At lower levels of irradiance, the cone receptors have a greater influence on the pupil size than the melanopsin receptors. In mice that have been genetically modified to comprise red cones (modified using knock in, a genetic engineering method that involves the insertion of a protein coding cDNA sequence at a particular locus in an organism's chromosome), the cones account for all pupil responses at low irradiances (<<NUM><NUM> photons/cm<NUM>/s: for <NUM> light, this photon density corresponds to about <NUM> lux). At higher irradiances, cones play a reduced role. It is at this point that melanopsin phototransduction in the retinal-transduction pathways via melanopsin receptors becomes the dominant driver for pupil response. For longer exposure durations, the red cone contribution to the pupil response drops and the melanopsin sensitivity increases.

The synchronisation of the circadian rhythm is mediated by direct input from the intrinsically photosensitive retinal ganglion cells (ipRGCs) in the eye. Rods, cones and melanopsin receptors can all contribute to the input coming out of the ipRGCs. The functional contributions of rods, cones and retinal circuits to these ipRGCs are not fully understood Experiments in mice that lack functional rods, or in which rods are the only functional photoreceptors, showed that rods were solely responsible for photoentrainment (i.e. alignment of a circadian rhythm of an organism to light) at low light levels. This means that at low light intensities the action spectrum for photoentrainment is dominated by the rod action spectrum. This peaks at roughly <NUM> in humans.

Rods are also capable of driving circadian photoentrainment at photopic intensities (i.e. intensities used in normal daylight) at which they are incapable of supporting visually guided behaviour. Using mice in which cone photoreceptors were ablated, it was found that rods signal through cones at high light intensities but not at low light intensities. Thus rods use two distinct retinal circuits to drive ipRGC function to support circadian photoentrainment across a wide range of light intensities.

Research has also shown that in the first quarter of a <NUM> hour lasting nocturnal light exposure, <NUM> light was equally effective as <NUM> light at suppressing melatonin secretion. This suggests a significant contribution from the three-cone visual system (λmax = <NUM>) during this part of the light exposure. However, during the latter part of the light exposure, the spectral sensitivity to <NUM> light decayed exponentially relative to the <NUM> light.

Moreover, for phase-resetting responses at lower photon densities (<<NUM><NUM> photons/cm<NUM>/s), green light appeared to be more effective compared to blue light. This is reversed at higher photon densities. In other words, at higher intensities (><NUM><NUM> photons/cm<NUM>/s), blue light tends to be more effective than green light for phase-resetting responses. This is depicted in <FIG>.

<FIG> depicts circadian phase shifts in response to retinal exposure to <NUM> (blue light, indicated as <NUM>) and <NUM> (green light, indicated as <NUM>) of various photon densities. The horizontal dashed line depicts the half-maximal phase-shift response. The vertical dashed lines depict the corresponding log half-maximum-response-values (ED50), which are indicated on <FIG> adjacent to their respective dashed line. Although the log ED50 for phase shifting to <NUM> light tends to be higher than the response to <NUM> light, the difference in log ED50 values is not statistically significant.

Rods can react to light in approximately <NUM>. However, it can take melanopsin receptors about <NUM> to react to changes in light. Further, cones can decrease the reaction of time of melanopsin receptors to the presence of light whilst rods can improve it. This is because the melanopsin receptors are very slow at switching off after light exposure, and cones do not saturate for high light exposures. Cones react fastest when detecting the absence of light and then act on the melanopsin system to signal that the lights are off. In contrast, rods are sensitive at very low light levels and provide a signal to the melanopsin system that the light is on.

At high light intensities (><NUM> lux) all photoreceptors will be activated and the melanopsin photoreceptor action spectrum (which peaks at around <NUM>-<NUM>) is expected to largely dominate the spectral sensitivity of non-image forming response(s). However, at intermediate and low light intensities, different photoreceptors may be operative at different moments of the light exposure.

When a pulse of light is initially incident on a user's eye (e.g. between a lights-off and a lights-on situation), the rods, cones and melanopsin receptors react in different ways depending on the intensity and/or duration of the light exposure. The rods have a relatively constant response to the newly incident light, contributing a flat-line signal in the formation of the signal output to the SCN. The cone response has an initial spike shortly after the lights are switched on. This spike decreases linearly with time and/or intensity. In contrast, the melanopsin receptors start to provide a response shortly after the spike in the cone response. The melanopsin receptor response starts from zero and increases linearly with time. At some point in time, the signal contribution to the SCN from the melanopsin receptors overtakes the signal contribution to the SCN from the cones.

In mice, non-image forming (NIF) effects of light exposures above <NUM>-Lux are almost exclusively determined by melanopsin receptors. In humans this threshold is expected to correspond to <NUM>-lux. Underneath this threshold rods dominate NIF responses (see Table <NUM>). In this context, the unit m-lux refers to melanopic-lux. For m-lux, the emission spectrum from a light source is weighted for its ability to stimulate the melanopsin photoreceptor. M-Lux is defined in the paper "A "melanopic" spectral efficiency function predicts the sensitivity of melanopsin photoreceptors to polychromatic lights" by <NPL>).

The situation at higher irradiances, within the melanopsin sensitivity range (i.e., above <NUM>-lux), is more complex. Cones remain sensitive and support vision under even the brightest illumination. In species in which cone vision is spectrally quite distinct from that of melanopsin (e.g., humans), cones may therefore strongly influence the spectral sensitivity of ipRGC-driven NIF responses. Under most daylight conditions, melanopsin is expected to be the primary influence on ipRGC activity.

The photoreceptor pathways for different NIF functions may also depend on different subtypes of retinal ganglion cells.

Thus, in the presently described system, when the system is used at a certain exposure duration of light level, it is configured to automatically select a spectral composition (which may include automatically selecting respective intensities for the selected spectral components) that matches the action spectrum of the photoreceptors that is most active for this light condition in determining the non-image forming response. This system can take into account the information provided in table <NUM> regarding the relative contributions of rods, cones and melanopsin containing retinal ganglion cells as a function of light intensity (and/or duration).

In one example, when coming from the dim light adapted state, the lights-on signal (i.e. when the light intensity is suddenly increased) to the ipRGCs is mainly given by rods. The "lights-on" rod signal continues to be of relevance for the duration of the light pulse. The "lights-off' signal (i.e. when the light is removed or is otherwise suddenly reduced) is given by cones. At higher light intensities, where cones are activated, cones play a role in signalling irradiance for NIF functions However, this is rapidly taken over by melanopsin receptors, making melanopsin receptors the main photoreceptor input to the SCN signaled by the retinal ganglion cells (RGCs). Rods may play the predominant role in driving responses at night and around dawn/dusk, with melanopsin taking over throughout most daylight. Light adaptation would limit cone influence under most conditions. However, this may allow cones to encode a somewhat different aspect of the light environment. Thus, the relatively sluggish adaptation recorded herein for melanopsin receptors would, in effect, introduce a high-pass filter, reducing the influence of the tonic component of cone activity under continuous illumination in favour of more phasic responses to sudden changes in irradiance. This would free cones to provide higher-frequency modulation of pupil size. The circadian clock, because of its long integration time for photic information, would be relatively refractory to these transient cone signals except under conditions of high temporal contrast i.e. pulsing, or otherwise discontinuous light. When referred to pulsing, it is understood that the light pulses may be periodic or aperiodic. It is also understood that the duration of each light pulse may vary. This would be advantageous if the targeted biological reaction of the user located in the area served by the lighting system changes over time.

In further experiments, various irradiances and durations were tested for their ability to suppress nocturnal melatonin and promote alertness. Table <NUM> specifies the light conditions used.

To generate this table, three monochromatic lights were used with λmax at <NUM>, <NUM> and <NUM>. This is represented in <FIG>, where the wavelength of each of the three peaks is labelled next to their respective peak. In total five light conditions were investigated for each wavelength. Three light pulses were matched for irradiance (<NUM> × <NUM><NUM> photons/cm<NUM>/s), but varied in duration (<NUM>, <NUM> or <NUM>) resulting in a different total photon content. An additional two light conditions were tested that were <NUM> and <NUM> in duration and administered the same total photon content as the <NUM> light pulse (<NUM> × <NUM><NUM> photons/cm<NUM>/s) as a (<NUM>).

To further illustrate these effects, we refer to <FIG>. These figures depict a percentage melatonin suppression (mean ± SEM) over time during irradiance or total photon content matched λmax <NUM>, <NUM> and <NUM> light pulses of different durations.

<FIG> corresponds to a thirty minute pulse duration with an intensity irradiance of <NUM>×<NUM><NUM> photons/cm<NUM>/s. The x-axis represents the time since the start of the light pulse in minutes. The y-axis represents a percentage of Melatonin suppression. In this example, <NUM> is a more effective wavelength than <NUM> for suppressing melatonin.

<FIG> corresponds to a ten minute pulse duration with an intensity irradiance of <NUM>×<NUM><NUM> photons/cm<NUM>/s. The x-axis represents the time since the start of the light pulse in minutes. The y-axis represents a percentage of Melatonin suppression. In this example, <NUM> is a more effective wavelength than <NUM> at supressing nocturnal melatonin.

<FIG> corresponds to a twenty minute pulse duration with an intensity irradiance of <NUM>×<NUM><NUM> photons/cm<NUM>/s. The x-axis represents the time since the start of the light pulse in minutes. The y-axis represents a percentage of Melatonin suppression. In this example, <NUM> and <NUM> wavelengths are about equally effective at suppressing nocturnal melatonin.

In relation to these findings, it is noted that cone photoreceptors appear to contribute more to non-visual (or non-image forming) responses at the beginning of a light exposure and at low irradiances. However, during long-duration light exposure and at high irradiances, melanopsin appears to be the primary photopigment driving circadian responses.

Thus, knowing the variance of the phototransduction pathways and how they vary with exposure-intensity, the spectral composition of a light exposure can be set for enhancing a particular biological effect. This spectral composition can be set using wavelength, duration and intensity.

As discussed, according to the present disclosure, there is provided a controller <NUM> for controlling the lighting of an area, and in particular the spectral composition of the lighting. The controller <NUM> is configured to control the spectral composition and/or the intensity of the light produced by the lighting system in dependence on the duration of the light exposure, e.g. the intended duration of use as indicated by a user of the lighting system.

In embodiments, the spectrum and/or intensity of the light output may depend on the temporal contrast of the lighting, for example depending on whether the light output comprises discontinuous light stimuli or light pulses. For example, the light pulses may be less that <NUM> minutes and may be repeated. This can be selected by a user or may be otherwise configured to match an absorption spectrum of, for example, the m-cone (i.e. the cone that responds best to medium-wavelength light). At low intensities (i.e. below <NUM>-lux), the predetermined time program may comprise a first time interval of between <NUM> seconds and <NUM> minutes. The predetermined program may comprise a first time interval of between <NUM> seconds and <NUM> minutes. The predetermined program may comprise a first time interval of between <NUM> seconds and <NUM> hours. In this first time interval, the spectrum may be enriched with rod activating light (approximately <NUM>).

In further embodiments, the spectrum and/or intensity of the light output may also depend on the light intensity of the area to be lit by the lighting system.

The following presents different examples.

In this example, the controller <NUM> is configured to select a spectral composition with the aim of maximising melatonin suppression in a user located within the lighting area controlled via the predetermined time program for different light exposure durations. Consequently, a predetermined time period of the pulse length is taken as the predetermined emission period for configuring the spectral composition.

When the pulse duration is short (i.e. less than <NUM>) and low intensity the devices automatically uses <NUM> light.

When the pulse duration is long (more than <NUM>), the device automatically uses <NUM> light. This arrangement exploits an effect displayed in <FIG>.

In this example, the controller <NUM> is configured to change the spectral composition over time with the aim of maximising melatonin suppression in a user within the lighting area controlled via the predetermined time program.

If the user sets the emission period to longer than <NUM> minutes, then during the first interval of the emission period (e.g. for the first <NUM> minutes) the device automatically uses <NUM> light. After <NUM> minutes, the device may automatically switch to <NUM> light. This technique exploits the effect displayed in <FIG>.

If on the other hand the user sets to emission period to shorter than <NUM> minutes, the device automatically uses <NUM> light for the entire duration.

It is noted that alertness can develop differently from melatonin suppression. It has been found that for exposures longer than <NUM> minutes, light having components around <NUM> are more effective at inducing alertness than other wavelengths.

In this example, a predetermined time program is pre-configured based on knowledge of the emission duration taken into account as a method step performed by the system designer at the design stage. The predetermined program is configured to change the spectral composition over time with the aim of maximising melatonin suppression in a user within the lighting area controlled via the predetermined time program. This system aims to use rods to support the ipRGCs response to newly incident light (i.e. during a "lights-on" scenario). In this embodiment, it is assumed that the user has set the time of the emission period to cover at least three intervals: the first interval, the intermediate period and the second interval detailed below.

During the first interval of the emission period (ranging from <NUM> to approximately <NUM>-<NUM>), the predetermined program is configured to cause <NUM> and <NUM> spectral components to be used by the lighting system. The latter (<NUM>) component is selected to use rods for extra ipRCG support. After the first time interval, there is an intermediate period in which the predetermined program uses light having a spectral component of around <NUM>. An intermediate period starts after expiry of the first interval and lasts for up to <NUM> minutes. At the end of the intermediate period, there is a second time interval during which the lighting system is configured to have light having a spectral component of <NUM>. This type of arrangement exploits the effects outlined in relation to Table <NUM>.

In this example, the predetermined time program is configured to change the spectral composition over time with the aim of restricting the nocturnal melatonin suppression in a user within a lighting system. It may do this by recruiting cones to support the ipRGC response to the absence of light.

During the last interval of a an emission period of a light pulse of duration t<NUM>, where ti is set by e.g. a user, the predetermined time program may be configured to include extra <NUM> spectral components in the light emitted by the lighting system. This spectral component utilises cones to signal the end of the light exposure by means an extra "lights off" cone input pathway to the ipRGCs. When any melanopsin activation has occurred, this has the effect of reducing the melanopsin activation in a shorter time period after ending the pulse. This allows for, assuming the lighting system is being used at night time when users of the system desire sleep, a reduction in the melatonin suppression action of the ipRGCs, which enables a faster return to sleep for the user following a nocturnal awakening or bathroom visit. This technique is advantageously applied for light pulses that are designed to minimise or otherwise reduce melatonin suppression, for instance a light pulse that avoids using any blue light around <NUM>, or one that uses only light having a wavelength greater than <NUM> light. The last interval may have its own associated duration of between <NUM> and <NUM> minutes from the end of the emission period.

In this example, the predetermined time program is configured to change the spectral composition over time, in dependence on the duration for which the light source is configured to emit light, to restrict or enhance the nocturnal melatonin suppression by a lighting system that emits white light.

Example <NUM> is similar to the examples mentioned above. However, there is an additional cone or rod input receptive to light pulses of white light of various colour temperatures. For example, the spectral composition and intensity can be changed over time to enhance circadian phase shifting by a lighting system e.g. a light system that includes a discontinuous cone (m-cone, with <NUM> absorption peak) addressing light component with an emission period of less than <NUM> minutes. The cone component may be inactive for at least <NUM>% of the time. The cone component may be inactive for at least <NUM>% of the time.

In embodiments the lighting system takes the form of a system for illuminating a space such as a room or outdoor space. However, the system may also be implemented in other forms. <FIG> schematically shows an alternative implementation in a display apparatus. The display apparatus <NUM> comprises the backlight unit BL, a pixilated display device DD, and a controller CO. The controller CO receives the input signal IS, which represents an image, and supplies data and control signals DA to the display device DD, and a control signal CB to the backlight unit BL. The image may be a natural scene (photo, video) or may be computer generated. The control signal CB controls the spectrum of the light source(s) <NUM> in the backlight unit BL. The controller CO may comprise a timer to control the timing of the different phases of the sequence of the different spectra Sl and S2. The backlight unit BL may comprise the controller <NUM> (see <FIG>), which provides the current/voltage to the light source(s) <NUM> to obtain the light L for illuminating the display device DD. For example, the display device DD is an LCD or DMD. For example, the back light unit may comprise fluorescent tube(s) and/or LEDs.

The present lighting system and apparatus described herein may be implemented in several applications, such as for example: office lighting (e.g. to improve early morning activity and to reduce after-lunch fatigue), hospital lighting (e.g. to reduce sleep inertia of medical staff upon nocturnal wake-up), care home lighting (e.g. to reduce day-time napping of elderly to improve nocturnal sleep duration and sleep quality), control rooms (e.g. to obtain sustained alertness during <NUM> hours operation and night shift work) and automotive lighting (e.g. alternating in-car exposure to low intensity red and blue LEDs to improve driver alertness). The particular biological response in a user located within the area to be lit by the lighting system is used to select the spectrum (in addition to the duration). The particular biological response may be input by an intended user of the system (e.g. the user intended to experience the particular biological response). The particular biological response may be input by a system administrator who is not the intended recipient of the particular biological response.

For example, the light sources may comprise a full spectrum light emitting device and (switchable) filters to generate the different spectra. Such filters may comprise electrochrome, electrophoretic, liquid crystal cells comprising (dichroic) dyes or based on electrowetting.

The present system may be combined with existing dynamic lighting systems. For example, a sequence of sub-sequences is added in the morning to further improve the alertness of the subject. The first sub-sequence of this sequence has the three phases, while the successive sub-sequences have three or two phases. Such existing dynamic lighting systems vary the color temperature and intensity of a light source over the day. However, these prior art lighting systems do not provide the sequences of the three phases, and change the color temperature of the emitted light very slowly during transition periods of one hour or more.

Claim 1:
A lighting system for illuminating a space, the lighting system comprising:
at least one light source (<NUM>) comprising a plurality of lighting elements which are configured to emit different colours of light allowing a spectral composition of light emitted by the at least one light source (<NUM>) to be controlled by turning the plurality of lighting elements on and off in different combinations and/or by controlling their relative intensities; and
at least one controller (<NUM>) configured to:
receive an indication of a pre-selected duration of an emission period for which the at least one light source (<NUM>) is to emit light;
control the at least one light source (<NUM>) to emit light for the pre-selected duration of the emission period; and
select a composition of a first spectrum of the light emitted by the at least one light source (<NUM>) to be a first spectral composition during at least part of the emission period, the first spectral composition suitable for generating an ipRGC mediated non-visual response at a user located in the space,
characterized in that the at least one controller (<NUM>) is configured to select the composition of the first spectrum in dependence on the pre-selected duration of the emission period and taking into account information regarding relative contributions of rods, cones and melanopsin photoreceptors as a function of duration, thereby engendering the ipRGC mediated non-visual response at the user.