Help with LED's please?

[Bizibilder]

I've just been to Maplins to buy some bits and bobs to make a light box. Among them were some white LED's Maplin code N50GK. There is nothing on the pack to tell me anything about them! nor is there anything on their website! Does any one have a catalogue that they could look in to see the spec?

The only additional info I have is "White LED 8000mcd 5mm".

Either that or can someone suggest how to wire them up? I reckon that I need four (or six?) in the light box (one in each corner seems to be a favourite set-up). Any guesses what resistor(s) I may need and whether to wire in series or parallel? My preferred supply would be 9volts.

As you can see an LED tyro!!

Thank you.

[Psychobilly]

Chances are Vf is going to be around 3.6V and If max around 30mA so your going to want around 200R 1/4W series resitor to run them close to flat out off 9V use higher resistor values to dim them...

You can parallel up the individual Series Resitor-LED combos... Thats the simple way to do it...

http://led.linear1.org/1led.wiz

The calculator will recommend the nearest E-12 series Resistor (220R) and has also recommended a 1/2W resistor... although the actual dissipation is less than 1/4W it doesnt hurt to go bigger...

The other option is to put two leds in series with a resitor of around 60R on each side of the box...

Peter...

[Bizibilder]

I've just been playing by risking one (expensive!!) LED and a few resistors and have managed to set up a simple series circuit from "so bright it hurts my eyes" (330 ohm I think) to "a bit too dim" at 100Kohms (I think those values are correct!!) - so I have some experimenting to do.

Thank you Peter!! As always you are so quick to respond with useful help! That little calculator is useful!

I think I will run each LED as a "seperate" series loop from the battery ie 4 circuits for 4 LED's - Is that what you mean by "parallel up"? i.e. start at the +ve - wire - resistor - led - wire - -ve and then repeat the same four times?

[Psychobilly]

Yep... although two lots of 2 leds and a single resistor in series will be slightly more efficient...

As somone who uses lots of LED's it never ceases to amaze me how they have come on in the last few years...

I know have a very Astro unfriendly LED head torch with a Single CREE LED which runs of 4 AAA NiMH cells and is much better than the bulky sealed led acid powered Halogen headlamp i used to use...

Peter...

[Bizibilder]

Thanks again for your help - I've got to get the box built first!

[martin_h]

Here's a series/parallel circuit :-

[Bizibilder]

Thanks Martin! By the way - nice Observatory! Iremember watching the build.