Is LED Street Lighting Bad for Your Health?

Misinterpretation of AMA report distracts from the real problems

The American Medical Association’s (AMA) recently issued report, “Human and Environmental Effects of Light Emitting Diode (LED) Community Lighting,” highlights many important issues regarding the implementation of street lighting to avoid negative environmental and health effects.

Unfortunately, on the subject of potential negative health effects of LED street lighting, the report has been misinterpreted by online media and even by the International Dark-Sky Association (IDA). The report has been boiled down to a sound bite along the lines of: “AMA says LED streetlights are bad for your health! (unless they are 3000K)”. This is really unfortunate, not just because it’s wrong, but because it puts attention solely on the issue of color temperature, distracting from the other very important issues raised in the report.

Jumping to Conclusions

Here are some examples of misinterpretations and misstatements.

• From NPR:
• Bright, Bluish-White LED Streetlamps Disrupt Sleep Cycles, AMA Says
• …Not true. The AMA report does not say this.

• From takepart.com:
• LED Streetlights Are Good for the Earth, Bad for Humans and Wildlife
  “Studies have shown that white LED streetlights are five times more powerful at suppressing circadian rhythms than the high-pressure sodium lights they are replacing, the AMA noted.”
• …Not true. The AMA report does not say this.

• From the International Dark Sky Association blog:
• “Not only is blue-rich white LED street lighting five times more disruptive to our sleep cycle than conventional street lighting, according to the report…”
• …Not true. The AMA report does not say this, either.

What the AMA Really Says

Here is what the AMA report does say (emphasis added):

• “It is estimated that a “white” LED lamp is at least 5 times more powerful in influencing circadian physiology than a high pressure sodium light based on melatonin suppression. Recent large surveys found that brighter residential nighttime lighting is associated with reduced sleep time, dissatisfaction with sleep quality, nighttime awakenings, excessive sleepiness, impaired daytime functioning, and obesity. Thus, white LED street lighting patterns also could contribute to the risk of chronic disease in the populations of cities in which they have been installed.
  Measurements at street level from white LED street lamps are needed to more accurately assess the potential circadian impact of evening/nighttime exposure to these lights.”

All the AMA report is saying is that it has been estimated that an LED source (of undefined color temperature) could potentially have 5 times the melatonin-suppressing effect as a high-pressure sodium source. (High-pressure sodium was the lamp source commonly used in street lighting before the arrival of LED). What the report neglects to mention is that the exposure to these two sources would have to be of sufficient intensity and duration to have any effect at all. It cites no evidence that the intensity and duration of exposure typically experienced from street lighting is sufficient to have any melatonin-suppressing effect.

The “recent large surveys” mentioned in the report refer to two epidemiological studies which looked for correlations between outdoor light at night, and obesity and sleep disruption. The measurement of outdoor light at night was derived from satellite imagery, with no information on spectral content (“color”) of the light. Since the satellite data used in the studies was from 2001 to 2009, the lighting was most likely high-pressure sodium, and certainly not LED. The studies show an association between obesity and sleep disruption and the level of outdoor lighting, but no causal effect. But even if a causal connection was proven, it can’t be connected to “blue” light, and would have been a problem long before the advent of LED street lighting.

In this RPI/LRC study, computer modeling was used to predict the potential melatonin-suppressing effect of exposure to street lights. The authors estimate that if you stood on the street under 5900K (high “blue” content) LED street lighting for one hour you might experience a small effect.

The AMA report also notes that the percentage of “blue” light in a 4000K LED source is 29%, vs. 21% for a 3000K LED source. Even if exposure to LED streetlights did have a negative health effect, 3000K instead of 4000K probably would not make much difference, based on the marginal difference in percentage of “blue” light.

And most importantly, the AMA says that further study is needed to assess potential health impacts from street lighting. Agreed!

Is Warmer Better?

There are reasons to use 3000K sources in outdoor lighting, such as reduced sky glow (see Ian Ashdown’s Color Temperature and Outdoor Lighting), glare reduction, design aesthetics, or personal/community preference. Until recently, there was a reason to not use 3000K LED, due to significantly lower energy efficacy compared to 4000K LED. But with recent improvements in LED technology, this difference in efficacy is very small, negating the disadvantage.

But, there are also possible reasons to use 4000K sources in some outdoor lighting applications. A study by Clanton & Associates and VTTI showed that 4000K LED street lighting resulted in significantly better ability of drivers to detect pedestrians at greater distances, compared to the other higher and lower color temperatures tested. This might make 4000K the best choice from a safety standpoint on streets with pedestrians and cyclists. Research from RPI shows that perceived outdoor scene brightness is higher with higher color-temperature sources. If you accept the premise that you need less light (fewer photopic lumens) from 4000K street lighting than from 3000K street lighting, then a 4000K street lighting system could use less energy, and create less light pollution than a 3000K system…possibly.

It’s a complex problem with no simple answer. So let’s use 3000K sources for all the good reasons, but not for some presumed public health benefit.

Let’s Keep Our Eyes on the Ball

We should be concentrating our efforts on reducing overall light levels, putting the light only where it’s needed, and controlling glare. This is where we can have a real impact on reducing light pollution and negative environmental impact. I'd hate to see a future where all the streetlights are 3000K, but we are still over-lighting our streets and parking lots.

And when it comes to the effects of light on health, we should be focusing our attention on interior lighting, lighting for shift workers, and light from display screens. This is where there is solid evidence that the quantity and the “color” of light can have negative (and positive) health effects.

For other perspectives on this issue, read the comments from the US Department of Energy and The National Electrical Manufacturers Association, and the detailed analysis from The Lighting Research Center at RPI.

To the AMA: Please Hire a Fact-Checker

A final comment on one blatant error in the AMA report, that is of special interest to me—the report says: “In Cambridge, MA, 4000K lighting with dimming controls was installed to mitigate the harsh blue-rich lighting late at night.”

The truth is that the adaptive dimming system was planned from the beginning of the project to reduce energy use and limit light pollution. The decision to use the adaptive dimming system had nothing to do with mitigating “harsh blue-rich lighting”. I know this because I was intimately involved with the design of the conversion of Cambridge’s street lighting to LED.

The Cambridge lighting control system is still the largest street lighting adaptive dimming system in the US, as far as I know, and is significantly reducing light pollution in our City. Other cities should be following Cambridge’s well-studied lead, and not take media sound bites or one line excerpts from this AMA report as accurate recommendations on how to minimize negative environmental or human health effects.