The first study we can find that examines how light affects chicken egg production is from 1934. E.L. Dakan found that red artificial lights gave a greater egg yield than other colours, and blue light produced the least number of eggs. Since then, there have been many papers (often with conflicting results, probably because of the type of lighting used) examining specific wavelengths, durations and intensities of light on egg laying.

While red light gives you more eggs, these eggs tend to be smaller than for other colours. Er et al (2007) found that blue light gave shorter eggs than other colours. Green light seems to increase egg quality and many new chicken farms are using green LEDs in their lighting.

Hassan et al (2016) also included shifts from red to green LED light in their study, and showed that this gave a similar yield to pure red light. Considering the effect of green light on egg quality, this could be the best idea.

The causes for these effects are diverse. Green light appears to be activating retinal photoreceptors, possibly increasing serotonin levels. Red light stimulates hypothalamic extra-retinal photoreceptors through deep tissue penetration, which regulate reproduction.

Knowing all of this, it does make you wonder how urban lighting could affect humans…