Streetlighting Concerns

I submitted the following letter to the editor to the Dodgeville Chronicle this evening:

Dear Editor:

Have you noticed the gradual transformation of our streetlights in Dodgeville, Mineral Point, and other communities in SW Wisconsin?  The light source in our streetlights is changing.  High Pressure Sodium (HPS), which has been in use for decades and produces a orangish-white light, is being replaced by light emitting diodes (LEDs), producing a whiter light.

What’s not to like?  LED’s many advantages include: efficiency, longevity, instant-on and instant-off, and dimmability, to name a few.  But Alliant Energy is installing new streetlights that produce white light that is too blue, and the illumination levels are about 2.6 times as bright as the high pressure sodium streetlights they are replacing.

Lighting specialists use a term called “correlated color temperature” or CCT (in Kelvin) that allows us to compare the relative “warmness” (redder) or “coolness” (bluer) of  various light sources.   The illumination provided by candlelight has a CCT around 1500 K, HPS around 2000 K, an incandescent light bulb around 2800 K, sunrise/sunset around 3200 K, moonlight around 4700 K, and sunny noon daylight around 5500 K.  The higher the color temperature, the bluer the light.

Higher color temperature illumination is acceptable in workplace environments during the daylight hours, but lower color temperature lighting should be used during the evening and at night.  Blue-rich light at night interferes with our circadian rhythm by suppressing melatonin production, thus reducing sleep quality, and several medical studies have shown that blue light at night increases the risk of developing cancer, most notably breast cancer.  Even low levels of blue-rich light at night can cause harm.  While it is true that something as natural as moonlight is quite blue (4700K), even the light of a full moon provides an illumination level of just 0.01 foot-candle, far dimmer than street lighting, parking lot lighting, and indoor lighting we use at night.

LED streetlights are available in 2700K, 3000K, 4000K, and 5000K.  I believe that Alliant is installing 4000K streetlights in our area—I certainly hope they are not installing any 5000K.  What they should be installing is 2700K or 3000K.  These warmer color temperature lights are no more expensive than their blue-white counterparts, and the slightly higher efficiency of the blue-white LEDs is entirely nullified by over-illumination.

Even considering a modest lowering of light level with age (lumen and dirt depreciation), these new LED streetlights are considerably brighter than the HPS lights they are replacing.  Just take a look around town.  What is the justification for higher light levels in our residential areas, and when was there an opportunity for public input?  In comparison to older streetlights, the new LED streetlights direct more of their light toward the ground and less sideways or directly up into the night sky, and that is a good thing.  But now the illumination level is too high and needs to be reduced a little.

If you share my concerns about blue-rich lighting and illumination levels that are often higher than they need to be, I encourage you to contact me at oesper at mac dot com.  I operated an outdoor lighting sales & consulting business out of my home (Outdoor Lighting Associates, Inc.) from 1994-2005, and wrote the first draft of the Ames, Iowa Outdoor Lighting Code which was unanimously adopted by the city council in 1999, so I am eager to work with others in the Dodgeville area who are also interested in environmentally-friendly outdoor lighting.

David Oesper
Dodgeville

Blue Light Blues

One by one, all of our warm white lights are being replaced by cold, harsh, bluish-white LEDs.  And it is happening fast.

Everywhere.  In our streetlights, our workplaces, even our homes.  How do you like looking into those blue-white vehicle headlights as compared with the yellow-white ones we have been using since the automobile was invented?

LED lighting is the way of the future, don’t get me wrong, but we should be specifying and installing LED lights with a correlated color temperature (CCT) of 2700K or 3000K—with few exceptions—not the 4000K or higher that is the current standard.

Why is 4000K the current standard?  Because blue-white LEDs have a slightly greater luminous efficacy than yellow-white LEDs.  Luminous efficacy is the amount of light you get out for the power you put in, often measured in lumens per watt.  But should luminous efficiency be the only consideration?  What about aesthetics?  In addition to luminous efficacy, there are other, more significant ways to reduce power consumption and greenhouse gas emissions:

  • Use the minimum amount of light needed for the application; no need to overlight
  • Use efficient light fixtures that direct light only to where it is needed; near-horizontal light creates annoying and visibility-impairing glare and light trespass, and direct uplight into the night sky is a complete waste
  • Produce the light only when it is needed through simple switches, time controls, and occupancy sensors; or, use lower light levels during times of little or no activity

Even the super-inefficient incandescent light bulb (with a CCT of 2400K, by the way), operating three hours each night uses less energy than the light source with the highest luminous efficacy operating dusk to dawn.  Think about it.

In my town, as in most now, the soothing orange 1900K high pressure sodium (HPS) streetlights are being replaced with 4000K LEDs.  That’s a big change.  It will completely transform our outdoor nighttime environment.  Warm-white compact fluorescents are 2700K, and even tungsten halogen bulbs are 3000K.  Do we really want or need 4000K+ LEDs?

We are currently witnessing a complete transformation of our illuminated built environment.  Not enough questions are being asked nor direction being given by citizens, employees, and municipalities.  The lighting industry generally wants to sell as many lights as possible at the highest profit margin.  We as lighting consumers need to make sure we have the right kind of light, the right amount of light, and lighting only when and where it is needed.

Higher color-temperature lighting of 3500K or higher is often specified for office lighting during the day to more closely match daylight color temperature, but all to often this type of lighting is also being specified for nighttime use.  Lower color temperature lighting of 2700K or 3000K should be used for residential lighting and any other lighting that is primarily being used after sunset, such as streetlighting, parking lot lighting, and security lighting.