FAO Tamer.
As promised here is the website for working out LED's.
LED's for beginners is well worth reading before you try anything yourselff (it'll save you money on components)
LED Center has some good information on how they work and for working out which components you need use
THIS PAGEWhich looks like this:
For the majority of dio's people will use 9V batteries but others will work fine (I've used much smaller for scorch but I'll stick with 9V for this tutorial). so type 9 into the top box. I used this
Superbright LED for my backpack. To work out the forward voltage click on specification and scroll down to forward voltage, in this case for the Blue LED its 2.4V, so type that in. For the Forward current type in 20mA (as suggested by the help guide) and finaly 1 for the number of LED's. Click wiring diagram and design my array. This will produce this outcome:
The wizzard will show you the various displays but wiring diagram is the easiest to understand. It also tells you what size resistor you need, in this case a 330 ohm resistor is needed.
Incedentally if you are just using 1 LED there is no need to use a 9V battery as most of its power will be wasted by the resistor as heat, but try adding more LED's to the wizzard and you'll see changes to the diagram and the resistor size. eg: 6 LED's needs 2 100 ohm resistors.
And finally for those who aren't aware
Spookymufu's Hoth Dio over at Rebelscum is well worth a look at for info and ideas on lighting and how to connect it to a mains supply.