LED Lighting and Dark Skies

Are LEDs good for dark skies?

Unfortunately, no… they could be, but as they are presently being used, they are almost always not. Not even close.

he average energy savings when using LED instead of high-pressure sodium (HPS) luminaires amount to 19–26% for single-sided, staggered and opposite layouts, although they are frequently negligible if mesopic effects are not included. The total costs of the LED lighting solutions, even including mesopic effects, are 1.36 to 6.44 times higher than those of the comparable HPS lighting solutions. Therefore, LEDs are questionable for street and roadway lighting.

Tucson has demonstrated a more aggressive approach, but still left significant benefits on the table by switching to white LED instead of an amber LED, and Tucson had more to lose due to their now abandoned amber lighting standards.

So the conclusions are clear – switching to white LEDs from the current yellow light technologies using sodium lamps saves only a little energy, much less than is being touted, unless lighting is dramatically reduced. But sky glow light pollution in the vast majority of retrofits is dramatically increasing.

How could LEDs help dark skies?

  • First and foremost, use yellow LEDs (not low-CCT white LEDs)! NBA LED with a spectrum similar to LPS (0.4x the sky glow impact of HPS), or PCA LED with a spectrum similar to HPS (0.7-1.6x the impact of HPS) should be used, or at worst filtered warm-white LEDs (1.5x the impact of HPS). These are not the most efficient LEDs at present, but can be a good tradeoff to balance energy and dark sky impacts.
  • Take advantage of LED dimming technologies to dim or turn off lights when activity or traffic levels justify it.

…And for any light type:

  • Only light roadways when a full assessment of costs (both fiscal and environmental) and benefits, including fiscal, environmental, and safety, shows overall benefits.
  • Always use fully shielded fixtures.
  • Use the lowest illumination level possible.

Come to FDSC for the best in dark skies information and recommendations!

To celebrate, promote, and protect the glorious dark skies of Flagstaff and northern Arizona.