Street Lights and Distances

I have never seen underground street lights!

Perhaps some miscreant has buried them all.....

One road coming into Prosser, WA, USA, passes under the landing approach to the airfield. There they have street lights about 12 feet high, rather than 20 or 25, or whatever is usual.

Ketchikan, AK, USA, has a crosswalk with flashing amber lights set into the street. That 's almost underground! Also a big surprise on first encounter, as in "what in hell is this?"

I meant to say street lights being fed from a power source under ground or over head? LOL Sorry for the confusion.

Rules of Thumb depend on municipal codes. What is yours?

The height would depend on the amount area the light is to cover which would also determine the lamp output in what you are trying to illuminate.

In my experiences with overhead lighting, 35 years as an electrician, I have found that manufactures usually have distances above grade for there fixtures. Some fixtures have an adjustment for the lamp base to match height above grade. I would suggest that if you are looking at a new installition, then you would check with the manufacturer their line of fixtures for that height. If you have existing fixtures, then again check with the manufacturer for the mounting height. Mounting too low means brights spots and is a waste of energy. Too high means that the area will be underlit.

Vic

You may want to check with a tech engineer at one of the major street light manufacturers.

When I worked on parking lots in the past where we had lighting for security purposes we always hired an electrical engineer experienced in street lights. There are several factors involved in determining the correct street lamp:

1). candle power output,

2). height of fixture above ground,

3). spacing of lamp posts,

4). overlapping of illumination area to produce a minimum lumen rating. Offhand, I don't remember what that value was.

5). Type of lamp employed .....halogen, sodium high pressure, mercury, etc etc.

I do remember that the engineer that we hired and the street light manufacturers both utilized some sort of software to model the effects of street lights based on the factors that I listed above, especially the lumen values where the light output from separate street lights overlapped.

Also, check with the local power company and ask them what the minimum Lu mens value they use when installing street lights. Also, various larger police departments have set guidelines for street lighting. You may also want to check the US Army Corp of Engineers (USACE) website for Guideline Specifications and the Engineering Manuals (EM-####) regarding design procedure of security lighting and street lighting. You may also want to check our the lighting chapter in Merritt's Civil Engineering Manual....I seem to remember that something about street lighting was covered in it. You may be able to find that text in one of the free ebook sites!

This should give you a head start at arriving at the answer you seek. Please let us know how you make out, okay?

Hope you have a very Merry Christmas & Happy New Year.

We need an emotioncon with a Santa hat or Reindeer Antlers!!!!!! LOL Hello CR4 Admin, did you see my request??????? ***GRINZ***

Lumens is not a measure of illumination. The lumen output for a light is the same, no matter how high it is mounted, or how far from the curb, or how far from the next light. A 400 Watt Metal Halide light provides about 20,000 lumens of light, initially. Lamp lumens deteriorate over time, but that still has nothing to do with height or distance. Footcandles is the most commonly used value in the utility industry.

It depends on power output of your lamps,the area to be installed,how busy the area is,topography.Actually it varies from place to place.

Check yr local spec.

Patrick Whowha

When I first read the post I thought you were asking how far horizontally from the curb, but since you say 10 - 25 feet I guess you mean vertically above the road. I attended a major manufacturers outdoor lighting school in North Carolina and their indoor lighting school in Cleveland and spent several years doing street light layouts for an electric utility. Horizontally, I tried to keep the lights 2 feet over the street. That way most of the light was on the street, but still there was some on the sidewalks, assuming you are using a type 2 or type 3 pattern, which is an elongated pattern so that it goes up and down the street. Type 5 is a round pattern and is used more for area lighting such as a back yard or residential area. Mounting height depends upon the application. If you are only providing small lighting at an isolated intersection, then stay close to 25 feet. Uniformity is the ratio of light to dark. It doesn't really matter in an isolated intersection, but if you are doing a major roadway, then 3 to 1 is the recommended level. Mounting height will depend upon the size of the light, the width of the roadway and the type of road. Different road traffic pattens will require differing levels of footcandles on the roadway. No single solution fits all cases.