LEDs

LED stands for light emitting diode.

They come in multiple forms and shapes. Here are some of the more popular sizes

Packages

3mm - very tiny also common

5mm - very common throughole

10mm - uncommon, pretty fat led, awesome to play with

0805 - surface mount

1206 -

PLCC-2 -

PLCC-4 - often used in bicolor leds

PLCC-6 - often used in tricolor leds

millicandela mcd

10 nice moderate indicator

100 pretty bright indicator

1000 very bright, look for a diffusor if you intend to use it

5000+ really bright, things start tasting blue, hopefully this is a flashlight

10,000 You should not ever look at this directly

mcd to lumen calc

http://led.linear1.org/lumen.wiz

Colors

625nm AlGaInP - 2.1V Brilliant Red

617nm - 2.1V Amber

590nm - 2.2V Yellow

527nm InGaN - 3.4V Brilliant Green

470nm InGaN - 3.4V Blue