Daylight sensor for automated window shading
View Patent ↗A daylight sensor for automated window-shading applications that incorporates at least one (and optionally more than one) of three aspects: an optimized Field-of-View (FOV), angle-diversity sensing (via at least two sub-sensors with different FOVs, whose outputs are processed in a particular way to yield the overall sensor output), and multi-spectral sensing (via at least two sub-sensors with differing spectral responses and, optionally, different FOVs, whose outputs are processed in a particular way to yield the sensor output). These aspects improve the correlation between the sensor output and the subjectively-perceived daylight level (especially under glare-inducing conditions, such as in the presence of low-angle direct sunlight), thereby enabling more effective automatic control of daylight admitted into a room.
1. A method of operating a window-shading device to block glare produced by direct sunlight, said method including the steps of:
(a) obtaining a sunlight signal from a sunlight sensor and a reference signal from a reference sensor, said sunlight sensor having a first spectral response and said reference sensor having a second spectral response, said first spectral response overlapping an atmospheric transmission window, said second spectral response overlapping an atmospheric transmission window, said first spectral response being displaced toward longer wavelengths with respect to said second spectral response whereby said sunlight signal is less sensitive than said reference signal to Rayleigh scattering of said direct sunlight by the atmosphere;
(b) obtaining a glare signal which increases with said sunlight signal and decreases with said reference signal; and
(c) closing said shading device if said glare signal exceeds a threshold.
2. The method of claim 1 wherein said first spectral response overlaps a near-infrared region and said second spectral response overlaps a visible region.
3. The method of claim 1 wherein said glare signal changes more with changes in said sunlight signal than with changes in said reference signal.
4. The method of claim 1 wherein said first spectral response overlaps a visible region and said second spectral response overlaps a near-ultraviolet region.
5. The method of claim 1 wherein said first spectral response overlaps a visible region and said second spectral response overlaps a visible region.
6. A system to operate a window-shading device to block glare produced by direct sunlight, said system including:
(a) a sunlight sensor to produce a sunlight signal and a reference sensor to produce a reference signal, said sunlight sensor having a first spectral response and said reference sensor having a second spectral response, said first spectral response overlapping an atmospheric transmission window, said second spectral response overlapping an atmospheric transmission window, said first spectral response being displaced toward longer wavelengths with respect to said second spectral response whereby said sunlight signal is less sensitive than said reference signal to Rayleigh scattering of said direct sunlight by the atmosphere;
(b) processing means to obtain a glare signal which increases with said sunlight signal and decreases with said reference signal; and
(c) a controller to close said shading device if said glare signal exceeds a threshold.
7. The system of claim 6 wherein said first spectral response overlaps a near-infrared region and said second spectral response overlaps a visible region.
8. The system of claim 6 wherein said glare signal changes more with changes in said sunlight signal than with changes in said reference signal.
9. The system of claim 6 wherein said first spectral response overlaps a visible region and said second spectral response overlaps a near-ultraviolet region.
10. The system of claim 6 wherein said first spectral response overlaps the visible region and said second spectral response overlaps the visible region.