DIY Moonlight photo completion pics

[Anonymous]

Currently I use a 30 inch 'magtinic' NO bulb, pointed at the roof of the canopy, as a moonlight. Works great, and was extremely cheap and easy to set up. No glitter lines though...

 

[Anonymous]

Ok, I am in the process right now, and I gots two questions - why the resistor and what voltage to set the power adapter at? The LED's light up with or without the resistor, and they light up at different voltages.

Help educate me please!

Thanks.

:mrgreen:

 

[smlacy]

You have to use Ohm's law (V=IR) To figure out the correct resistor value for any LED, you have to know the mA (milli Amp) rating of the LED.

So, for example, lets say that you have a LED thats rated for 20mA. (as almost all of them are) And its rated for 3 to 12 volts. Let's say you're going to run with 12V, because thats what most non-adjustable transformers will produce.

You use the equation "Voltage = Current * Resistance" to figure out the needed resistance to generate the correct current. Current is always measured in Amps, Resistance in Ohms. So, for this example, we have:

12V = 0.020A * Resistance

Solve for resistance, to get

Resistance = 12 / (0.020) = 600 Ohms.

If you were running at 5V, you would have:

5V / (0.020A) = 250 Ohms.

Don't worry too much about exact Ohm values. You'll be hard pressed to find a 600 Ohm resistor. Just use a 470 Ohm and you'll run it "a little hot" (~25 mA) or to take no risks, use a bigger resistor and run a little dimmer. Or, you can chain together multiple resistors to get the correct value.

You can commonly run LEDs at Amperages that greatly exceed their rated capacity (up to 5x or 10x their rating) They will burn brighter, and have significantly shortened life if run for extended periods, as I expect we all are. To test, just hook up the LED with no resistor. See how long it lasts. (note: I'm joking)

Other things to remember: LEDs should produce *no* heat while running. You should feel *absolutely nothing* from them. If you can feel some heat, you're running too much current through there and you need a bigger resistor.

Steve

 

[kleinfreak]

Much better than my answer would have been Steve. I would have given some Homer answer like "There's too much of the stuff, where it's all about the things, and it doesn't last....oooohhhh cupcakes!"

I used a 47ohm (yes 47) and mine are burning out already...see what happens when you don't take your time childeren.

 

[Anonymous]

Thanks Steve! What about running multiple LEDs on the same wall wart? Does that change the math?

 

[Anonymous]

I like my single 25W party light over my 75. The glimmer lines are da bomb. I like the idea of using LEDs though.

Louey

 

[smlacy]

You can wire up multiple LED/Resistor pairs in parallel and all the math is still the same. If you want to only use one Resistor, just sum up the number of Ohms and you're done.

In all cases, make sure you're putting the resistors on the Positive side.

Steve

 

[kleinfreak]

In all cases, make sure you're putting the resistors on the Positive side.

Dumb it down for us Steve...Long or Short side?
:?

 

[Anonymous]

Marked for Archiving

 

[smlacy]

I'm pretty sure the long one is the anode and therefore goes towrads the positive side (goes towards +5V)

Steve

 

[Anonymous]

Yep, long side positive (and its the only way it will light up). I used 470 resistors and 8 leds. Used a a mini dv tape box as a project box.