LED street-light installations have deficient design

Article By : John Dunn

We have seen street lighting technology evolve, but not always to public benefit. These recently-installed LED street lights created a very scary safety hazard.

Older street lights in many communities have been getting replaced with LED street lights. In my opinion, those replacements have brought about a colossal calamity.

Please examine this photograph of nighttime lighting near my home and note the street areas that fail to receive light and the example of street light glare. The older street lights did not have these two faults.

photo of the a poorly-lit streetFigure 1 Deficient nighttime lighting leaves gaps and creates glare.

I have noticed that new light fixtures that have been mounted along many streets do not provide total area illumination. In Figure 1, several parked cars are just barely visible.

Drivers who are just exiting parked cars, bicyclists, and pedestrians, some walking their dogs while wearing dark clothing, are easily concealed from view in the unlit areas. Their concealment constitutes a grave danger.

Adding to the problem, the LED lights on my street inflict dazzling glare. I am forced to squint when looking in their general direction and I suspect that my pupils are forced to contract, thus further diminishing my ability to see whoever may be present in the zones of darkness. I do not believe that I am alone in suffering from that effect. This need not have been the case.

Please examine the photograph in Figure 2 of nighttime lighting where differently designed LED street light fixtures provide total and uninterrupted area illumination without glare but with dramatically better visibility.

photo of a parking lot lit by LED street lightsFigure 2 Differently-designed LED street lighting fixtures provide uninterrupted illumination without glare.

In Figure 2, the light outputs from overhead light fixtures overlap so that there are no zones of darkness, and nobody is apt to be concealed from view. Light from the overhead fixtures is bright, but not actinic. Looking directly at those fixtures gives me no impulse to squint. Why, you might ask, is that so?

Recognizing that other opinions may run to the contrary, to see why the Figure 2 benefits accrue, we may compare what I call a “deficient” light fixture to what I call an “adequate” light fixture.

photos comparing LED street lights with glass lenses and translucent domesFigure 3 LEDs set behind transparent glass lenses shine light primarily downward in a narrow cone (left), while fixtures with light diffusers offer better coverage (right).

The darkness zones of Figure 1 arise from the use of “deficient” street light fixtures like the one on the left in Figure 3. LEDs are set behind transparent glass lenses through which each shines an extremely high intensity white light primarily downward in a narrow cone. A close-up look at those LEDs may illustrate the deficiency of this design (Figure 4).

photo of the LEDs in a street lightFigure 4 A close-up look at the “deficient” fixture shows why it illuminates only a limited area.

The group of LEDs taken together illuminates only a limited area directly beneath the fixture. Some light gets directed off to the sides, which is not enough for useful illumination but has enough sideways glare to adversely affect night vision. I find the glare directly beneath the fixture to be utterly overwhelming.

The absence of darkness zones in Figure 2 arises from the use of street light fixtures with light diffusers like the one on the right in Figure 3. High intensity white light is diffused and is thus delivered to a much wider area beneath each fixture. Overlaps of the light outputs of these fixtures avoid the creation of darkness zones. The diffusion effect also avoids the creation of glare, much like the rippled glass enclosures of the older gas-filled street lights acted as light diffusers that did not produce glare.

As seen in Figure 4, the LEDs of the “deficient” fixture are devoid of any light diffusion provisions. It might be put forth that such light diffusion along residential streets would cause unwanted illumination of nearby homes. To my knowledge that was never an issue with earlier street light fixtures made with sodium vapor lamps nor, going further back in time, with the use of mercury vapor lamps and their light diffusing domes.

However, if unwanted illumination is a concern, I have no doubt that non-imaging optics technology, which can offer effective diffusers, would cast their light outputs properly in parallel to the street directions and away from houses.

Are we ever going to start saving lives by remedying these street-lighting hazards or would doing so somehow be too costly?

This article was originally published on EDN.

John Dunn is an electronics consultant, and a graduate of The Polytechnic Institute of Brooklyn (BSEE) and of New York University (MSEE).

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