Lighting system that maintains melanopic lux levels at the eye regardless of distance to user

1. A light emitting system comprising:

a lighting device configured to provide light;

a sensor configured to sense a distance parameter d between the lighting device and a user; and

a control system is configured to control one or more lighting properties selected from a spectral power distribution of the light, and a light intensity I of the light as function of the distance parameter d for maintaining the melanopic illuminance at the user constant within a predetermined range of melanopic lux values,

wherein the lighting device is comprised in a portable device, and

wherein the control system is configured to maintain in a mode a value of I/(αd n ) constant over at least part of a range of the distance parameter d, wherein I is the luminous power of the light of the lighting device, and wherein 0<α≤1 and 1≤n≤2.

2. The light emitting system according to claim 1 wherein the control system is configured to scale the light intensity I of the light with the distance parameter d linearly or exponentially.

3. The light emitting system according claim 1 , wherein the control system is configured to maintain in a mode the value of I/(αd n ) constant over at least part of a range of the distance parameter d.

4. The light emitting system according to claim 1 , wherein the control system is configured to maintain a predetermined melanopic illuminance, wherein light emitting system further comprises a user interface configured to allow a user determine the predetermined melanopic illuminance.

5. The light emitting system according to claim 1 , wherein the control system is configured to control the melanopic illuminance to be not larger than a predetermined maximum melanopic illuminance value and/or to be not smaller than a predetermined minimum melanopic illuminance value.

6. The light emitting system according to claim 1 , wherein the control system is configured to control the one or more lighting properties selected from the spectral power distribution of the light, and the light intensity of the light as function of the distance parameter d, while maintaining one or more other lighting properties constant, wherein the one or more other light properties are selected from the group consisting of the correlated color temperature and the color point.

7. The light emitting system according to claim 1 , wherein the control system is configured to adapt the one or more lighting properties selected from a spectral power distribution of the light, and the light intensity of the light as function of a change in the distance parameter d, wherein the adaptation is only executed after a predetermined period when the change is permanent within the predetermined period.

8. The light emitting system according to claim 1 , wherein the control system is configured to one or more of adapting the one or more lighting properties selected from a spectral power distribution of the light and the light intensity I of the light as function of an average change in the user-related parameter, and gradually adapting the one or more lighting properties as function of a change in the distance parameter d.

9. The light emitting system according to claim 1 , wherein the control system is configured to control the light according to a predefined scheme, and wherein the control system is further configured to adapt the light relative to the predefined scheme as function of the distance parameter d.

10. The light emitting system according to claim 1 , comprising a portable device, wherein the portable device comprises a display comprising the lighting device, wherein the portable device further comprises the sensor and the control system, wherein the portable device is selected from the group consisting of a smartphone, a laptop, a tablet, a wearable device, a personal digital assistant, a game console, a media player, and a navigation device; and wherein the sensor is configured to sense one or more of infrared radiation and reflected light.

11. The light emitting system according to claim 1 , wherein the lighting device comprises a source of deep blue light, a source of blue light, a source of green light, and a source of red light, which are independently controllable by the control system, wherein the source of deep blue light is configured to generate light selected from the wavelength range of 400-440 nm, and wherein the light of the source of deep blue light has a peak maximum having a smaller wavelength then a peak maximum of the light of the source of blue light.

12. A method of controlling light, wherein one or more lighting properties, including the spectral power distribution and the intensity of the light are controllable, the method comprising: providing light from a portable lighting device; sensing a distance parameter d between the lighting device and a user; and controlling one or more lighting properties selected from a spectral power distribution of the light and a light intensity of the light as function of the distance parameter d for maintaining the melanopic illuminance at the user constant within a predetermined range of the melanopic lux values, and maintaining in a mode a value of I/(αd n ) constant over at least part of a range of the distance parameter d, wherein I is the luminous power of the light of the lighting device, and wherein 0<α≤1 and 1≤n≤2.

13. A computer program product, when running on a computer which is functionally coupled to a portable lighting device, is capable of bringing about the method as described in claim 12 , wherein the lighting device is configured to provide light, wherein one or more lighting properties, including the spectral power distribution and the intensity of the light, are controllable.

14. A light emitting system comprising:

a lighting device configured to provide light;

a sensor configured to sense a distance parameter d between the lighting device and a user; and

a control system is configured to control one or more lighting properties selected from a spectral power distribution of the light, and a light intensity I of the light as function of the distance parameter d for maintaining the melanopic illuminance at the user constant within a predetermined range of melanopic lux values,

wherein the lighting device is comprised in a portable device, and

wherein the light emitting system is configured to maintain a value of Φ mel /(αd n ) constant over at least part of a range of the distance parameter d, wherein Φ mel is the melanopic flux of the light of the lighting device, and wherein 0<α≤1 and 1≤n≤2.

15. The light emitting system according claim 14 , wherein the control system is configured to maintain the value of value of Φ mel /(αd n ) constant over at least another part of a range of the distance parameter d.

16. The light emitting system according to claim 14 , wherein the control system is configured to control the one or more lighting properties selected from the spectral power distribution of the light, and the light intensity of the light as function of the distance parameter d, while maintaining one or more other lighting properties constant, wherein the one or more other light properties are selected from the group consisting of the correlated color temperature and the color point.

17. The light emitting system according to claim 14 , wherein the control system is configured to adapt the one or more lighting properties selected from a spectral power distribution of the light, and the light intensity of the light as function of a change in the distance parameter d, wherein the adaptation is only executed after a predetermined period when the change is permanent within the predetermined period.

18. The light emitting system according to claim 14 , wherein the control system is configured to one or more of adapting the one or more lighting properties selected from a spectral power distribution of the light and the light intensity I of the light as function of an average change in the user-related parameter, and gradually adapting the one or more lighting properties as function of a change in the distance parameter d.