The venerable Light Emitting Diode. They're everywhere, included in
every piece of electronic equipment, from remote controls for your T.V.
set to status
lights for your electric razor. They serve a multitude of purposes, and
a seemingly endless variety of colors, sizes and brightness. This
is geared toward the case modding community, but the information
should be of value to anyone needing to employ LED's in a custom
project. I'll start off with a general discussion of the different
types of LED's. Following that, you can read about some uses of LED's,
how to wire them correctly, and even how to modify existing LED's that
you may have in your
What are Light Emitting Diodes? In the early 1960's Nick Holonyak Jr.
"A light-emitting diode is essentially a junction
between a region of p-doped semiconductors having an excess of holes
and an n-doped region having an excess of electrons. At the junction
between the two regions, the electrons and holes can combine. Because
electrons occupy a higher conduction band than holes, they have more
energy, which must be released during the process of recombination."
Ok, that stuff is mostly above my head, but not to worry. The main
thing to realize is that, unlike a lamp, which is just a piece of hot metal
enclosed in a vacuum, an LED is actually a much more sophisticated and efficient
light producer. They draw less current than a lamp, and their color output is
much more defined. Another distinction to keep in mind, is that LED's are
diodes, meaning that they only like to pass electrical current in one
direction. This can lead to a lot of trouble for first-time users. There
are ways to determine the correct polarity of LED's, which we will talk about
LED's come in an almost endless variety of form factors, from the venerable
"bullet" shape, to square and even surface-mount styles.
Typically, projects involving case modding usually concentrate on the bullet
shapes, and maybe a square or rectangular shape for case-status lights and
such. One way to get up to speed on the various form factors is to check
out an electronics catalog. One fine example of this is the Jameco
catalog. When I was doing a lot of custom case work, Jameco always gave me good
service. There are other fine retailers out there, including Digikey,
Allelectronics, and even Radio
Shack. Although I will reference Jameco's catalog more than once, most of
the terms used here are industry standard.
The typical bullet LED comes in two basic sizes, T1 and T1-3/4. The T1
- 3/4 is the larger, and is very common. Here is a size comparison chart for
these two varieties.
||Length of bulb tip
||0.119 in / 3mm
||0.197 in / 5 mm
|1 ||2 ||3 ||4 ||5 ||6 ||7 |
|8 ||9 ||10 ||11 ||12 ||13 ||14 |
|15 ||16 ||17 ||18 ||19 ||20 ||21 |
|22 ||23 ||24 ||25 ||26 ||27 ||28 |
|29 ||30 ||31 || || || || ||