New street lights with least amount of light pollution?

Posted 01 September 2022 - 06:01 PM

Shielding is the most critical aspect to consider. However, almost all LED streetlights are fully shielded these days since it is more energy efficient, so I would be surprised if any of the options were not already full cut off. The only ones that might not be shielded are period-style or decorative fixtures, although shielded options are available for those too. 

The next most importance aspect is the intensity. While some may argue that brighter is safer, it's important to make sure your city understands that this is not always the case. Excessively bright lights cause blinding glare, and also force our eyes to adjust to the bright conditions, thus we are less able to see well in darker areas. The unfortunate side affect of this is that even more light becomes necessary for adequate vision in areas adjacent to a bright light, when if the light was dimmed the extra lighting would not be as necessary. 

You can determine the intensity with a cheap light meter from amazon or other retailers. They may not be perfect but good enough for a simple comparison. 

Third, the color matters. The more amber the color, or lower the correlated color temperature (Kelvin), generally speaking the less impact it will have on the night sky. Blue light (shorter wavelengths) scatters more in the atmosphere than red light (longer wavelengths), so blue contributes more to skyglow, and it is not linear. Blue scatters about 4x more than red. Blue light is what disrupts circadian rhythms, plants, and animals the most. So from an astronomy and environmental perspective, less blue or no blue at all is best. 3000K or below is what the IDA currently recommends, but they indicated that their recommendations will likely be even lower for streetlights soon. Near McDonald Observatory in Texas, some communities have opted for 2200K for their streetlights (astronomy and environmental concerns being the primary motivation). 

Some may claim that white / blue light is safer, but there isn't really much rigorous evidence for this, and what evidence exists is highly context dependent. Our eyes naturally adjust for the color cast of a scene. Bright blue lights can make driving in fog or rain especially difficult. But white/blue also provides greater contrast in good conditions, albeit at the cost of losing our ability to see in unlit areas, so there's debate over what is safer. It may be that the pros and cons of each pretty much cancel each other out. 

Lastly, consider adaptive controls. Many streetlights come with an option for adjustable brightness or timing. So for example if a resident complains about a light, the light could be dimmed to be less intrusive. Or lights could be turned off late at night when fewer people are active to help save energy. The energy savings of dimming / timing strategies often more than offset the cost of the controls over a few years. 

Here is a great video about a town retrofitting their streetlights with LEDs, done right: https://www.youtube....aye8Uog&t=1794s

Edited by SirHumHum, 01 September 2022 - 06:04 PM.