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Video courtesy of the Department of Energy
Video courtesy of the Department of Energy

Glare in general is a problem outdoor just because you've got a dark environment, and you're adding a bright light source in. And so that's one of the primary issues. And then when we move to LED, we move from these large sources down to a bunch of little, tiny sources. And that causes glare. So you're getting the same amount of light out of a much smaller space, and people have a greater glare impression.

The things that we need to remember: We've got the intensity from the luminaire, the number of luminaires, the size of the luminaire, and the height or the angle of the luminaire.

In roadway disability and discomfort glare-- basically disability glare limits your ability to see something, so you're disabled that way. How this works is, as the light goes through your eye, it hits all the medium of your eye-- so the cornea, the lens, the vitreous humor, all those things-- and it scatters. So every time it hits something, it scatters. And it keeps scattering. And so it basically casts a veil of light across your retina.

Discomfort glare is causing discomfort or irritation in the driver. There are some other things that we talk about but don't really have good metrics for. One is nuisance glare. It's just sort of a light source that's kind of bugging you but really not causing you any discomfort or pain.

The other problem in roadway is discomfort glare is periodic as you go underneath these luminaires. And so it's, I've got discomfort. I don't have discomfort. I've got discomfort. I don't have discomfort. And it's very fatiguing as that goes along.

But one of the fundamental things about glare is that it's dependent on your adaptation limits. So if you've got a dark area and you start tossing up these really bright light sources, then you're going to have more glare.

There's a lot of cool luminaires out there. I think the variety of approaches that we're seeing in terms of lighting a space and different opportunities that LED provides, whether it's on a roadway cutting sharp backlight drop-off to reduce light trespass or in a parking lot where you've got a wide open space that gives you good color rendition as a person walks through.

Boy, it's got a little too much glare for me.

Yeah. It's pretty hot, isn’t it?

Yeah. It is. It's a lot smoother in light distribution, but that glare.

From a design standpoint reducing direct glare, use only the amount of light you need where you need it. So if you've got an intrinsically dark area, certain times of the day, you can certainly dim it down. You can adapt it. If you control the light source and make it relative to the environment around you, then you've got an automatic reduction.