Replacing Acton Streetlights

Bernard Kosicki

The Outdoor Lighting Advisory Committee (OLAC) has published a series of articles on outdoor lighting recently, discussing glare that can be caused by unshielded lights.  Glare is the unobstructed view of the bright lamp or reflector portion of an outdoor light.  Glare puts a stress on our seeing and reduces our effectiveness to see darker parts of the scene.  A big fraction of the lights we see while driving are of course streetlights, so it's important that these lights minimize glare and load on our vision.

Most of Acton's streetlights were installed from the late 1960's to about 1980- a period in which there was less awareness of the need to control glare for good vision- a principle that is now largely accepted in the outdoor lighting design community.  Our streetlights have a drop-refractor lens designed to shine light in all directions, and therefore produce glare.  More modern, glare-controlling streetlights can be seen around town in a few locations.  We can recognize these lights by their clear, flat glass lens that is horizontal to the ground- they are called "full-cutoff" (FCO) or fully shielded lights.  An internal reflector focuses the light into a cone onto the pavement below, and prevents light directly shining up into the sky causing sky glow.  Dean Charter, the Director of Town Property, has installed a number of these fully shielded lights along Hayward road, just uphill from the high school.  Driving down from ??? Lane at the top of the hill to the bottom, we can see only the light reflected from the road.  The glare from the lamps of these FCO streetlights is fully shielded from our view.

Besides producing glare, our current streetlights are also very inefficient in producing light from electricity.    Lamps such as high-pressure sodium (HPS) or metal halide (MH) are about one-and-one-half- to two-times more efficient.  This means that Acton could have the same light on the pavement with only a fraction of the electricity cost we are currently paying NSTAR for electricity (our current bill for streetlight electricity is about $57,000 a year).

OLAC will be proposing to the Town ways to finance replacement of our current streetlights.  Because of the large electricity savings, and also a energy-savings rebate currently offered by NSTAR encouraging towns to replace inefficient MV lamps, Acton could completely finance new streetlights WITHOUT increasing its current budget for streetlight maintenance and electricity.  Current estimates are that a loan to accomplish this replacement could be paid off within five years.  Every year thereafter, Acton would enjoy a reduced budget for streetlight operations.

Besides glare reduction and reduced costs to the Town, replacement of streetlights would have a significant environmental benefit by removing the Town's consumption of significant amounts of mercury found in the current mercury vapor lamps.  Although MV lamps must be disposed of properly, there will inevitably be some loss of mercury into the environment in the process of handling large quantities of lamps.  HPS lamps have much less mercury compared to the MV lamps.  The MH lamps have an intermediate amount of mercury, between that of HPS and the current MV lamps.

The primary drawback with HPS is that the pinkish-orange light from these lamps doesn't render colors as accurately as the MH lamps, although more modern versions of the HPS lamps are better.  Many people feel that wrongly sky-glow is caused only by HPS lamps, since their orange glow is very easy to see when lamps are incorrectly shielded or too much light is used for the job.  The truth is just the opposite, however; MH lamps really are worse at producing sky-glow, since they contain much more blue components of light which are much more easily scattered by dust and particles in the atmosphere-it is just that MH sky-glow is not as obvious since it doesn't have as distinctive color as HPS does.

HPS lamps are the more efficient than MH, requiring the least amount of electricity and energy for the same visible light output.  HPS has the longest useful life, and therefore is the most economical to maintain.  They are the least contaminating of the environment containing the least amount of mercury, and producing less sky-glow that similarly sized MH lamps.  For all these reasons, it is clear that high-pressure sodium lamps are the environmental champion outdoor lighting source at present.  Most environmentally sensitive professional lighting designers recommend HPS for streetlight use because of these factors.

OLAC welcomes comments by residents particularly on the issue of streetlight replacement; do you think that Acton should work toward replacement of its streetlights?  Would you prefer to see high-pressure sodium (HPS) or metal halide (MH) as the replacement lamp used?  Do you think that Acton's streetlights are in the right places? Please also give us your comments on any other outdoor lighting issue in Acton.  Please email us at O...@town.acton.ma.gov, or call the Planning Department at (978) 264-9636.