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(Aug 19, 2005)

When I was growing up, mostly just red and green LEDs where available. Amber (or yellow) versions existed too. But most of the time you saw red LEDs, since they were cheap to manufacture. They have the lowest wavelength, lowest power requirement, and a very distinct color, so they were sufficient for most uses. They've also been around the longest, since the lower wavelengths are cheaper and easier to produce (Actually, I believe infrared has been around longer, but being invisible light, I'm not counting them in this discussion).

Green LEDs became increasingly common as I grew up. In fact, in the home computer industry, green became the color of choice for power indicators, and red fell into the standard for hard drive indicators. This worked very well, taking advantage of two distinct colors for simple uses. A similar trend has continued with many video recorders, using green for power, and red (or amber) to show when it's recording.

Sometime in the 1990's, blue LEDs came on the scene. They were still expensive, but their arrival was very exciting for several reasons. First of all, blue is my favorite color, and I would finally have access to this (I have since replaced the power-light on my computer with a soft blue LED, for example). With a full spectrum of colors available, electronics manufacturers could do even more to choose colors for an aesthetic or meaningful purpose, rather than just based on availability. Also, blue was the missing component for being able to make white, and every color of the spectrum on the fly, for things like full-color displays. I didn't anticipate some of the drawbacks, however, and I've become more sensitive to what I consider to be abuses or "improper" use of LED lights.

It was discovered long ago that the human eye is most sensitive to green, and least sensitive to blue. So it would be a reasonable assumption that green LEDs, all things being equal, would appear piercingly brigt compared to other colors, right? Some are, but more often than not, green LEDs appear no brighter than their red or amber counterparts. My theory is that these LEDs were intentionally made slightly more dim, to have the same apparent brightness as the others. This is a good thing. You want LED displays and indicators to convey the information they're installed for, without being distracting or painful to look at.

So why is it that there are so many blue LEDs on the market that are distracting and painful? Having recently fallen in price to the point where blue could be used in commodity electronics without significantly impacting the prices, we're seeing them used everywhere. This happens all the time, of course. When something is new, it gets adopted, everyone gets carried away, and after a while the fad wears off. We may already be on the down-swing of this trend, however I've seen very few blue LEDs used properly, in my opinion.

In some cases you'll find a nice soft indicator-LED (indicators are LEDs that have a "frosted" surface, that appear to illuminate evenly and without casting a beam), which is very nice. Often times, you'll find high-intensity lens-LEDs (these are designed to set behind a light-guide of some kind, usually a cylindrical piece of plastic that allows the LED to be mounted some distance behind a removable panel, or something similar). The problem here is two-fold.

By over-compensating for the human eye's insensitivity to blue, extremely bright blue LEDs can be both distracting and painful. They can leave a significant after-image (yellowish usually) if you've looked at one for more than a few seconds, and in some cases they're unpleasant to look at.

Secondly, (and this is a common problem with other colors as well), many manufacturers don't seem to get the difference between an indicator LED and a lens LED. The lens versions appear very dim from the sides, and piercingly bright from the front. Electronics that panel-mount or flush-mount these LEDs make it hard to see the status of the lights from the sides, and yet hard to look at from the front. Indicator LEDs should be used here. Or the lens LEDs should be recessed behind a guide or a frosted window.

This also leads me into yet another complaint I have about LED usage. LEDs emit some light to the sides, and will leak into one another if not separated by something opaque. This is particularly noticable in some commodity network equipment, such as the inexpensive network routers and hubs you might buy at a local computer store. If you're too far to the side, it's not easy to tell which lights are running, since they all appear dimly lit.

Some of the high-end manufacturers have figured this out. Foundry Networks in particular does a beautiful job of making their indicators clear and distinct. However, you will probably never see this for yourself unless you work in a datacenter.

I think overall, the trends are improving. As LED-equipped electronics become more ubiquitous, vendors are starting to realize the importance of aesthetics in their designs. LEDs are being used more appropriately. The colors are being used more meaningfully, especially in datacenters where it seems that you will mostly see green, unless there is a fault or a warning somewhere.

As a hopeless geek, I love my blinky lights, and I'm surrounded by them every day. I look forward to seeing more product designers understand the minute details of the aesthetic choices that go along with the choice of semiconductors to use. In the grand scheme of things, this technology is still relatively new. As a society, we're bound to trip and stumble a few times. :)