Illinois’s Proposed Dark Sky Bill

SB 3037, the Dark Sky Act, is currently working its way through the Illinois legislature. The bill sets out to add dark sky requirements within the Illinois Stretch Energy Code. It would update the Illinois Stretch Energy Code requirements so that the Code contains separate residential and commercial components. It specifically proposes:

(A) outdoor lighting standards (light levels) of no more than 25% above ANSI/IES standards;

(B) light trespass from luminaire light sources measuring no greater than 0.1 lux;

(C) luminaires emitting more than 1,000 lumens emitting no more than 5% of their total lumen output above 80 degrees from nadir; and

(D) maximum correlated color temperature of outdoor luminaires of 3,000 Kelvin.

The light trespass <0.1 lux is concerning, as this is the level Dark Sky International (DSI) set for the most ecologically sensitive areas, and this level can be exceeded by moonlight. DSI’s own residential light trespass recommendation is “not to exceed 3 lux” (30 times the value in the Illinois bill). This is particularly concerning as residential lighting contributes a very small fraction of light pollution / sky glow compared to street and commercial area lighting. Some recent calculations by ALA Engineering Committee members have shown that one residential street light (5000 lumens at 4000K) produces 20-30 times the sky glow of one residential fixture (500 lumens at 3000K).

The bill would require a new stretch energy code adoption date no later than December 31^st, 2029. The stretch energy code could then be adopted by municipalities/AHJs. The full legislative text is available here.