Building Circadian Effective Spectra: An Open Source C Language Toolkit

Intrinsic circadian clocks control the sleep patterns of most species on the earth. Having a natural period ~10’ longer than 24 h, they must be reset to the natural day/night cycle daily. The critical input (Zeitgeber) “resetting” this internal clock is the temporal variation of the spectrum and intensity of light across the 24-h day. To develop artificial lighting that mirrors sunlight in an individually tailored, dynamic way to control melatonin suppression correctly and provide adequate vision on a 24-h circadian cycle, open-source code is needed to adjust and optimize the weighting of the various LEDs chosen for the system. Spectral differences between batches of LEDs and differences in room layout require code to fine tune the weightings of the LEDs. Making use of existing spreadsheets (CIE α-opic, CIE1931, CCT, Duv Tolerance (Duv (T)) (CIE 2017)) and the data concerning the LEDs spectral power distribution (SPD), power consumption, cost and spectra, open-source C-code was written to build spectra, calculate a spectrum’s visual and nonvisual optical parameters along with power consumption (a key practical concern). An evaluation function, suitable for use in either brute-force or AI-assisted optimization, was written. As an example, this was used to optimize parameters to aid in establishing tailored 24-h dynamic white lighting systems. Hardware was developed to implement the optimized spectra, and the lighting system was deployed in a long-term care environment.