Lighting system

1. A lighting system for illuminating a space, the lighting system comprising:

a light source comprising a plurality of lighting elements which are configured to emit different colors; and

at least one controller configured to:

receive an indication of a pre-selected total duration of an emission period for which the first light source is to emit light, the total duration of the emission period comprising a first time period and a second time period;

control the light source to emit light during the first and second time periods, wherein the at least one controller is configured to control the light source to emit light with a composition of a first light spectrum comprising a first wavelength during the first time period of the total duration, wherein the first wavelength is selected at least in part on the total duration of the emission period, the first time period, and

an action spectrum of photoreceptors that dominate in providing a non-image forming response, wherein the composition of the first light spectrum is suitable for generating a non-visual response at a user;

adapt the light emitted by the light source during the second time period such that the light source emits light with a composition of a second light spectrum comprising a second wavelength selected at least in part based on the total duration of the emission period, the second time period, and an action spectrum of photoreceptors that dominate in providing a non-image forming response; and

wherein the at least one controller is configured to control the lighting system to adapt the compositions of the first light spectrum and the second light spectrum in further dependence on the state of the circadian clock of a user within said space during the emission period, and an intensity or spectrum of illumination measured by a light sensor of an area adjacent to the space illuminated by the lighting system.

2. The lighting system as claimed in claim 1 , wherein the at least one controller is configured to adapt the composition of the first light spectrum in dependence on the first time period and total duration of the emission period and the second light spectrum in dependence on the second time period and total duration of the emission period by selecting spectral components of light to be emitted and intensities thereof.

3. The lighting system as claimed in claim 1 , wherein the intensity of the light emitted during the total emission period is pre-selected prior to the adaptation of the composition of the first light spectrum, the composition of the first light spectrum being adapted in response to the pre-selected intensity.

4. The lighting system as claimed in claim 1 , wherein at least one of the total duration of the emission period and the intensity of the light to be emitted during the total emission period is pre-selected by the user.

5. The lighting system as claimed in claim 1 , wherein the first time period or the second time period of the total emission duration is pre-selected from a range between 5 seconds and 30 minutes.

6. The lighting system as claimed in claim 5 , wherein the intensity of the first light spectrum or the second light spectrum is less than 18m-lux and wherein, in dependence on this intensity, the at least one controller is configured to include a spectral component having a wavelength of 505 nm.

7. The lighting system as claimed in claim 1 , wherein the at least one controller is configured to adapt the composition of the first light spectrum or the second light spectrum in dependence on whether the light is to be emitted continuously or discontinuously during the emission period.

8. The lighting system as claimed in claim 7 , wherein the light is emitted discontinuously in pulses of 10 minutes and the spectral composition of the light is matched to an m-cone absorption spectrum.

9. The lighting system as claimed in claim 1 , wherein the at least one controller is configured to adapt the composition of the first light spectrum or the second light spectrum wherein spectral components responsible for melatonin suppression in humans are suppressed.

10. The lighting system as claimed in claim 1 , wherein the at least one controller is operable to set a start point or end point of the emission period.

11. A display apparatus comprising a lighting system as claimed in claim 1 .

12. A method of controlling a light source, the method comprising:

receiving an indication of a pre-selected total duration of an emission period for which the light source is to emit light, the total duration of the emission period comprising a first time period and a second time period;

controlling the light source comprising a plurality of lighting elements which are configured to emit different colors, to emit light with a composition of a first light spectrum comprising a first wavelength during the first time period, wherein the method comprises selecting the first wavelength

at least in part based on the total duration of the emission period, the first time period, and an action spectrum of photoreceptors that dominate in providing a non-image forming response, wherein the composition of the first light spectrum is suitable for generating a non-visual response at a user;

adapting the light emitted by the light source during the second time period such that the light source emits light with a composition of a second light spectrum comprising a second wavelength, wherein the method comprises selecting the second wavelength at least in part based on the total duration of the emission period, the second time period, and an action spectrum of photoreceptors that dominate in providing a non-image forming response; and

and further adapting the compositions of the first light spectrum and the second light spectrum in further dependence on the state of the circadian clock of a user within said space during the emission period, and an intensity or spectrum of illumination measured by a light sensor of an area adjacent to the space illuminated by the lighting system.

13. A computer program product embodied on at least one non-transitory computer-readable storage medium and configured so as when executed on one or more processors of a lighting system to perform operations of the method of claim 12 .

14. The method of claim 12 , further comprising adapting the composition of the first light spectrum in further dependence on a duration of the illumination measured by the light sensor.

15. The lighting system as claimed in claim 1 , wherein the non-image forming response is input by an intended user of the lighting system.

16. The method of claim 12 , wherein the non-image forming response is input by an intended user of the lighting system.