Michael Lane LC

archived articles

Exterior Pedestrial Lighting
November 1996

You are walking down the sidewalk late one night, do you feel safe? Are you uncomfortable with the surroundings? Is the lighting helping or hindering your ability to identify other people on the sidewalk? Does the lighting provide an interesting, fun, attractive environment to be in?

For years, lighting for sidewalks, walkways, and many pedestrian areas has been an afterthought, with the lighting being provided by street lighting equipment. Maybe it is time to reverse this trend in our downtown areas: light the sidewalks and let the streets be lighted with the spill light. The luminaire would have a pedestrian scale, maybe 12-15 feet high, and the light would have a good color rendering to light the pedestrians and store fronts (NO HPS!). Of course, the lighting at the pedestrian-vehicular intersections would need to be a higher level, to provide identification to both the driver and the pedestrian to the possible dangers. This higher illumination level could be accomplished by a taller post light with a higher wattage lamp or multiple luminaires on a single post.

A experiment is just starting in The Dalles, Oregon that will test this above hypotheses. They have removed 28 existing High Pressure Sodium street lights in a portion of there business district and replaced them with 46, 14 foot high post lights using the Philips QL induction lamp. The initial response from the business owners and downtown shoppers has been extremely positive. Why the positive response? Well, the new luminaires have a pedestrian scale, 14 feet high versus 23 feet for the existing cobra heads, which enhances the downtown image. Also, switching from the low color rendering, yellow high pressure sodium to the high color rendering, white induction lamp also enhanced the downtown ambiance. Unfortunately, only time will tell how successful this change out will be.

From a wattage standpoint the new installation reduced the wattage by over 2500 watts. Assuming 60,000 hours for the rated life on the QL Induction lamp, this change will save over $6,000. This savings is for the energy reduction only and does not include the maintenance cost of relamping the HPS 2.5 times during the same 60,000 hours. Yes, there are twice the number of luminaires and posts, resulting in a doubling of the installation cost. Unfortunately the $6,000 energy savings will not nearly pay for the change out from HPS.

How then can this change out be justified?

• First, the quality of the visual environment is far more important that initial cost, or at least it should be. Pedestrians and shoppers are attracted to interestingly lighted areas, not just well lighted areas. It's time that lighting designers and electrical engineers, or anyone who specifies lighting equipment, start stressing to their clients that the cost, or even the energy consumption, is not the most important consideration when selecting a lighting system. The quality of the lighting design and the lighting system is the most important. We need to make architects & building owners understand the true value of a good lighting design. Lighting has a social value not just an economic value.

• Second, maybe there is something to the research that Sam Berman at Lawrence Berkeley Labs, Mark Ray at Lighting Research Center, and others have been doing on visibility with light sources rich in scotopic lumens. If the studies are correct, we could do the same lighting installation, but with less than half of the wattage? Now, then we would have both an economic benefit along with a social benefit. I know that I prefer, and can see better with, the white light of the Induction lamp, or Metal Halide lamp, than the yellow light of the High Pressure Sodium lamp.

In a very non scientific study, I have asked people who come through the Lab to judge the relative brightness of two identical color boxes. In one color box is a standard 70 watt HPS lamp with a color rendering index of 22. In the other color box is the Philips Comfort HPS lamp with a color rendering index of 65 (GE makes a similar lamp called the Deluxe HPS). Now according to the initial lumens published in the lamps catalogs, the standard HPS lamps produces 6400 lumens, while the Comfort HPS produces 4400 lumens. A 31% lower illumination level produced by the Comfort HPS: by the way, the actual measured difference is 25%. Without telling people which box has the higher light level, I ask them which one looks brighter. Generally more people respond that the Deluxe HPS is brighter or is as bright as the standard HPS. How can this be when the light meter measures 25% lower, unless the higher color rendering, more scotopically rich output of the Deluxe HPS lamp allows the eye to see better?

I understand the reasons for using HPS in street lights--long life and high lumens per watt--and maybe that is OK for vehicle-only areas like expressways. But in downtown areas, if we use pedestrian scale luminaires with low wattage light sources rich in scotopic lumens, maybe the lighting can provide more than just safety; maybe it can provide an environment that can help revitalize our downtowns. It sure is worth a try.