Check out this interesting peer-reviewed paper surveying the basic science and innovation opportunities surrounding circadian/melanopic response lighting, written by Robert Soler and Erica Voss of Bios Lighting.
I found one section particularly helpful, in understanding how circadian/melanopic response can be shifted without necessarily presenting the light as a cooler color temperature:
One way to think about this is as follows: Z stimulation results in bluer color perception, Y stimulation results in greener color perception, and X stimulation results in redder color perception. This blue perception from Z stimulation versus melanopic stimulation is key to disentangling visual perception from physiological effect. Z has highest sensitivity from 430 to 450 nm, whereas melanopic blue-green has highest sensitivity from 480 to 500 nm. Thus, a spectral power distribution can be derived with heightened melanopic stimulation without appearing cold in color temperature. Likewise, a spectral power distribution can be created that has less melanopic stimulation while still appearing cold in color temperature.Frontiers | Biologically Relevant Lighting: An Industry Perspective | Neuroscience (frontiersin.org)
I also appreciate this conclusion section and the following chart from their paper:
Compounding the Strategies for Brighter Days and Darker Nights
Standalone strategies for brighter days and darker nights are outlined in this article and while some individual interventions may not seem like they apply a space or application, the combination of these strategies compound their benefits to create a biologically relevant lighting environment.
For example, a person spends their day in the office under standard 3,500 K LED lighting with 300 lux at the task plane and 150 lux at the eye. A standard 3,500 K LED spectrum has a melanopic DER of about 0.51, thus the melanopic EDI at the eye is 76.5. The same person spends their evening in a home with luminaires populated with 2,700 K LED light bulbs. These luminaires provide approximately 50 lux at the eye. 2,700 K LED spectrum has a melanopic DER of about 0.4, thus a nighttime melanopic EDI of 20. This is a typical example of how light is biologically too dim for daytime use (76.5 melanopic EDI) and too bright for evening (20 melanopic EDI), with a day-to-night ratio of 3.8:1. Its not certain if more benefit would be gained from brighter days or darker nights, it is good practice to improve both and increase that day-to-night ratio.
At the office, the simple incorporation of a spectrally optimized daytime light source with a slightly cooler color temperature of 4,000°K will lead to a 58% boost in daytime biological potency. This would increase 76.5 melanopic EDI from the example to 121 melanopic EDI. While at home, incorporating spatially optimized light bulbs with a slightly warmer color temperature of 2,200°K lighting provides a 60% reduction in nighttime biological potency. This would decrease 20 melanopic EDI from the example to eight melanopic EDI. Combining these two strategies would increase the day-to-night ratio in the example from 3.8:1 to 15.1:1. This is a 392% increase in the delineation of daytime versus nighttime.
The proposed goal is to combine as many of these individual strategies and put them into practice (when possible) while maintaining excellent light quality, appropriate design aesthetic, and achieving user/occupant compliance. These strategies are itemized here:
For posterity a PDF is below: