Lighting system calibration
A method is provided of calibrating a lighting system to enable conversion between i) light output settings for a plurality of lighting channels of the lighting system, each channel having a respective color spectrum from a first set of color spectra, and ii) a light intensity at an area of interest for each of a second set of color spectra. The method derives a calibration matrix, based on a set default light outputs from the lighting channels, a mapping to light spectra to be measured, and light intensities measured at those light spectra. This calibration procedure takes advantage of the fact that using the same measurement device conventionally used for a simple calibration, it is possible to retrieve not only the total measured PPFD, but also partial PPFD values per spectral range.
1. A method of calibrating a multi-channel lighting system to enable conversion between i) light output settings in terms of luminous flux for each of a plurality of lighting channels of the multi-channel lighting system, each lighting channel corresponding to a respective color spectrum from a first set of color spectra, and ii) a light intensity in terms of illuminance at an area of interest for each of a second set of color spectra, the method comprising:
obtaining a set of total light outputs in terms of luminous flux values from the multi-channel lighting system, each one of the set being for a respective lighting channel when the lighting channel is operated at a respective calibration setting, as default stored calibration information;
obtaining a spectral distribution mapping S between the first set of color spectra and the second set of color spectra, as default stored spectral distribution mapping information;
setting each of the lighting channels to their respective calibration settings;
obtaining a measured light intensity in terms of an illuminance value for each of the second set of color spectra at the area of interest; and
deriving a calibration matrix K, based on the set of total light outputs in terms of luminous flux, the spectral distribution mapping and the measured light intensities in terms of illuminance, which calibration matrix provides calibration of the second set of color spectra.
2. The method of claim 1 , wherein the first set of color spectra has the same or a smaller number of spectra than the second set of color spectra.
3. The method of claim 2 , wherein the first set of color spectra has the same number of spectra as the second set of color spectra.
4. The method of claim 1 , wherein the method comprises obtaining or determining an inverse spectral distribution mapping S −1 .
5. The method of claim 1 , wherein the method comprises determining an inverse K −1 of the calibration matrix for use in converting between a desired light intensity in terms of illuminance at the area of interest and the required light output settings in terms of luminous flux of the plurality of lighting channels.
6. The method of claim 1 , wherein the first set of color spectra comprises three or more color spectra corresponding to three or more lighting channels, and wherein the second set of color spectra comprises three or more color spectra.
7. The method of claim 6 , wherein the first set of color spectra comprises deep red, blue, white and far-red, and the second set of color spectra comprises blue, green, red and far-red.
8. The method of claim 1 , wherein the light output settings in terms of luminous flux for each of a plurality of lighting channels are expressed in photosynthetic photon flux PPF, and the light intensity in terms of illuminance at an area of interest for each of a second set of color spectra is expressed in photosynthetic photon flux density PPFD.
9. The method of claim 1 , comprising deriving the calibration matrix K as:
K=S ·diag( S −1 ·PPFD cal )·diag( PPF cal|ch ) −1 ·S −1
in which:
PPFD cal is a vector of the measured light intensities in terms of illuminance values;
PPF cal|ch is a vector of the total light outputs in terms of luminous flux values;
S is a matrix defining the spectral distribution mapping;
S −1 is a matrix defining an inverse spectral distribution mapping; and
diag( . . . ) is the diagonal matrix operator.
10. The method of claim 1 , comprising measuring the light intensity in terms of the illuminance for each of the second set of color spectra at the area of interest.
11. The method of claim 1 , for calibrating a horticultural lighting system, wherein the area of interest at which the light intensities in terms of illuminance values are measured comprises a plant canopy.
12. A non-transitory computer readable medium comprising instructions which, when said instructions are executed by a processor of the multi-channel lighting system, cause the processor to perform the method of claim 1 .
13. A multi-channel lighting system comprising:
a luminaire having a plurality of lighting channels (CH 1 . . . Chn), each lighting channel (CH 1 . . . Chn) being controllable to provide light output in a particular color spectrum from a first set of color spectra;
a light sensor configured to measure light intensities in terms of illuminance at an area of interest, for each of a second set of color spectra;
a memory stored therein:
a set of total light outputs in terms of luminous flux values from the multi-channel lighting system, each one of the set being for a respective lighting channel when the lighting channel is operated at a respective calibration setting, as default stored calibration information, and
a spectral distribution mapping S between the first set of color spectra and the second set of color spectra, as default stored spectral distribution mapping information;
a processor configured to receive the measured light intensities from the light sensor, the processor configured to:
obtain a set of total light outputs in terms of luminous flux values from the multi-channel lighting system, each one of the set being for a respective lighting channel when the lighting channel is operated at a respective calibration setting, as default stored calibration information;
obtain a spectral distribution mapping S between the first set of color spectra and the second set of color spectra, as default stored spectral distribution mapping information;
set each of the lighting channels to their respective calibration settings;
obtain a measured light intensity in terms of an illuminance value for each of the second set of color spectra at the area of interest; and
derive a calibration matrix K, based on the set of total light outputs in terms of luminous flux, the spectral distribution mapping and the measured light intensities in terms of illuminance, which calibration matrix provides calibration of the second set of color spectra, the calibration matrix for converting between non-calibrated light outputs in terms of luminous flux per lighting channel (Ch 1 . . . Chn) and the resulting calibrated light intensity in terms of illuminance at an area of interest, for each of a second set of color spectra; and
the memory for storing therein the determined calibration matrix.
14. The lighting system of claim 13 , comprising a horticultural lighting system, wherein the area of interest comprises a plant canopy.
15. The lighting system of claim 13 , comprising an animal farming system, wherein the area of interest comprises location of animals.