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(Aug 19, 2005)
LEDs are one of my favorite innovations in electronics: simple little semiconductors
that produce light. LED stands for "Light Emitting Diode", and are the little blinky
lights that you see indicating that an electronic device is turned on. They show when
your VCR/Tivo is recording, when a line is in use on your desk phone, and when your
hard drive is active on your computer. You may even have an alarm clock whose display
is made up entirely of seven-segment LED numerical displays.
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
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. :)