erm, i want to run 12 volts to a voltage resitor and then run them at 5 volts
they all will be from the same place, same chracteristics
Chunga, that’s um goofy, lol… Just use the program Beth linked above and it will calculate the series / parallel circuit and resistor values for you. Just power everything with the 12vdc supply. I tried it and it’s pretty cool.
Uh, if he doesn’t know the forward voltage of the LEDs and current he wants to run them at the applet isn’t going to help. This is why I asked what type of LED. 
Chunga, got a link to the LED parts you ordered or something? All LEDs are not created equal. 8)
yea…i cant seem to find the link that robodude got me 
and yes, i dont know wat forward voltage is (nvm where to find it)
More than likely they are Silicon LEDs; so the voltage drop is 0.7 volts.
If you put them in series instead of parallel, you may not need the resistor at all!
With 12 volts, that would give you 0.8 volts per LED.
Just barely enough to light them. Maybe…
Also, most LEDs can stand up to 20ma (some up to 50ma) without being damaged. Most are happy with 5ma to 10ma…
So if you wanted to try a resistor (with the series setup), start at 600 ohms, and work your way down until you are happy with the brightness…
Also, most 12vdc batteries can vary up to 14vdc (open circuited measurement?) so it may be safer to start with the resistor just in case…
Or another trick is to use a potentiometer (linear preferably), in place of the resistor. Then vary the pot resistance until you are happy with the brightness; remove the pot; measure the resistance; then replace with the closest fixed resistor…
If it turns out that the LEDs are too dark, even with NO resistor at all; then you can try a combination of series/parallel…
Make two groups of LEDs; six (or eight, whatever) in parallel, then the two groups of six in series… Etc… or 3 parallel groups in series, etc…
MJL
Silly chunga, here are the specs on the LEDs:
MCD: 18,000mcd
Reverse Voltage:5.0V
Forward Voltage:3.3V Typical
DC Forward Current:20-30mA
Source Material: InGaN
Viewing Angel: 15 degree
Thanks Beth! That site is neat bookmarks.
Chunga, as the site shows, you could use a 3 x 20 array of LEDs with a 120ohm resistor in series with the 3 LEDs and simply have 12v powering them.
And as I told you before, the amperes will kill the LEDs more likely than the voltage would. I should know xD I ran a $2 LED (RGB T_T) at 12v and forget to add a resistor and poof it burned to a crisp with like 200mA running through it =/
lol, thanks robodude, anyway, so theres the information, and i plugged it into the link Beth gave me and it came up with 5 rows of 3 LEDs each, with a 100 ohm resistor at the end of each one 
(running at 25 mA)
well, off to the mall to fill my Simon mall gift card that doubles as a Visa 
, cya later
[size=59]Edited for spelling errors[/size]
Sure thing… But how you get 5 x 3 array? Thats 15… You have 60LEDs, no?
15 x 4 = 60
Oh woops 
He wants 15 LEDs per PCB! I didn’t notice that. sorry! :oops::oops:
yup, seamus got it correct, i will have 4 LED…towers/lines that will make night day
I didn’t get from his post that he didn’t know, or couldn’t get the specs.
happily, the LEDs and resistors will be getting here either tomorrow or wednesday
All I’m gonna say is 15x 18,000mcd LEDs operating in the IR range may be dangerous to your eyes so please exercise caution when handling these.
I second that cautionary note! The visible multi-thousand mcd LEDs are downright painful to look into.
i am not getting the IR LEDs for right now, just normal white 18,000 mcd LEDs and thank for the advice about the IR LEDs, i iwll be sure not to have too many and i will try and keep them sub 8-10 thousand mcd
Ah, well, at least with white LEDs you’ll know you are doing damage when you stare into them.
Oh and actually white explains the 3.3v forward voltage as well.
lol
stares into LEDs…ouch eyes bleed
why, do speccific colors have specific voltages? 
Different types of LEDs have different operating voltages, based on the semiconductor chemistry and method used to produce the light.
lol 
