Streetlights are not strong enough to upset your circadian rhythm

This post was researched and written by a member of the Streetlights Committee:

Recently, there has been a lot of attention given to the issue of light exposure and its impact on circadian rhythms. This is very appropriate given the proliferation of LED screens in mobile phones, computers and televisions. LED screens emit a type of blue light that, particularly in the evening hours, can significantly impact sleep patterns and lead to a difficulty sleeping. The current recommendation for good sleep hygiene is to limit use of phones and other devices with LED screens for 1-2 hours before bedtime. 

In contrast to LED screens, however, other lights used in homes do not significantly impact circadian rhythms. Melatonin is the hormone in our brains that regulates our circadian rhythms. Bright light, such as sunlight during the day, suppresses melatonin levels and signals daytime for our bodies. The influence of light on melatonin levels, however, only occurs with bright lights. Light influences circadian rhythms only at levels beyond 100 lux (100 lumens per square meter). Considering the typical family room lit up at night is 50-75 lux, one can imagine the intensity of light needed to impact circadian rhythms. Bright lights, such as the fluorescent lights used in office buildings, would affect melatonin levels and circadian rhythms; rooms inside homes are typically lit at a intensity less likely to. 

When we extend this discussion to street lights outdoors and the impact they can have, it is clear that they would not have an effect on individuals who are indoors many feet away. When standing on the sidewalk right next to the streetlights that would be installed on Springdale, the brightness is only 18 lux. The intensity of the lights dissipates as you move farther away. At 50 feet away, it is 3 lux. At 67 feet is it the brightness of a full moon, which is 0.3-1 lux. Inside a house, the brightness would be reduced both by distance and windows. All of these levels are far below the level that would be needed to have an effect on melatonin levels that impact circadian rhythms. 

In summary, although the impact of light on circadian rhythms is an important concern in our lives these days, much of the issue relates to our use of devices which use LED screens. The impact of other forms of light are nearly negligible unless specific rooms are lit at levels 1.5-2 times the intensity used in typical homes. Street lamps outside of a home would not affect melatonin levels given their very low intensity and how that intensity diminishes at distances many feet away from them. 

Sources on Circadian Rhythm:

• Duffy JF and Czeisler. Effect of Light on Human Circadian Physiology. Sleep Medicine Clinics. 2009; 4: 165-177 
• Zeitzer JM, Dijk DJ, Kronauer R, Brown E, Czeisler C. Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression. Journal of Physiology. 2000; 526: 695-702

Source for Springdale streetlight specifications: 

• King Luminaire Co. Certified Test Report No. LSC A003