Electronic Design

Turn Out Those Lights!

Though the latest blue LEDs have high luminous efficacy, and white LEDs do their part, they still are most environmentally friendly when they're dark.

Once again, most of the media missed the point. If you will indulge me, the whole point of Akasaki, Amano, and Nakamura’s blue LEDs is that you can turn them OFF and on again fast. It’s nice that they have high luminous efficacy. However, regardless of the few watts it takes to squeeze out a lumen, white LEDs are doing their best for the environment when they’re dark.

Look at a nighttime photo of the Earth from space. The place looks like a circus midway.  Four-fifths of it is covered in ocean, with a heck of a lot of desert. Despite that, the planet positively shimmers, regardless of where the dark side is at any given hour.

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The reason for that shimmer stems from the use of so much sodium and mercury vapor lighting – and the fact that we rarely turn those lights off, whether we happen to need them at the time or not. That’s because it simply takes too long to turn them on.  It’s necessary to generate plasma and strike a high-voltage arc through the light in order to make photons.  If you turn one off, it takes time to turn it back on. Even with tungsten lamps, you don’t want to turn them on and off very often due to added mechanical stress on the filament.

In contrast, with an LED, you’re just forward-biasing a diode when you turn it on, so you’re not creating much heat in the process.  (And you can tune the color-rendering index for a psychologically appropriate value by fooling with the phosphors inside the bulb.)

But the main point is that you can turn area lighting on and off as often as needed without a penalty. If nobody is on the fourth floor of the parking garage at 2 am, the lights can be out.  If I come in late to pick up my car, a proximity sensor can turn them on (it turns out the police like the lights coming on, because it tells them where there’s “action”).

The same principle holds for street lighting. No cars, no pedestrians, no need to burn the juice. Give the sergeant at the local precinct a tablet to turn them on. Give the beat cop an app to do the same thing.  There are probably several hundred applications begging to be developed, with interesting engineering challenges in terms of monitoring and security to make them challenging and differentiable.  For design engineers, tons of opportunities are lurking, especially on the communications side of the fence.

I have, in fact, been impressed with the rate at which surrounding communities are switching over to LED street lighting. However, it’s also disappointing to see it on all night long. That’s because turning the things out when there’s nobody around would mean somebody’s saving my tax money, a consummation to be wished devoutly.

Anyway, at least we’re keeping the people on the ISS awake.

TAGS: Components
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