Modding Need quick help with an LED problem.

I have a thread in electronics, but I need this mouse pad done asap, so I am posting a quick question here...I will show the finished result here a bit later, assuming this problem is quickly answered.

I have some blue leds. They work off of 5 volts, directly connected to a molex. At 5 volts, they are bright, and keeping your hand on them for more than a few seconds, burning. Not to the point that they melt plastic, but they will hurt your finger. They came with some resistors. Using one, the brightness drops down. Not as pretty, but not nearly as hot either.

These leds are going into a mousepad. I want these leds to last quite awhile. Running at 5 volts, am I shortening their lifespan or is it normal for LEDs to run hot like that? Should I go ahead and put in these resistors to get a longer life?

 

Running them directly off of 5v, yes, you are shorting their lifespan. The resistors are there to limit current to a safe level. For now, put the resistors in and deal with the diminished brightness. Later on, you can play with resistor values and see what works best for you. What'd be helpful is if you had a multimeter (refer to signature) to test how many ohms the resistor is and how much current the LED is getting when it is connected to said resistor. If it's around 20mA, then it's probably best not to toy with other resistors.

 

yeah definately put the resistors in if you want it to last

 

Ive got three multimeters. Never thought to use them.

/me runs into shop

 

Always use resistors with LED's even if its only something small in value. Overdriving your LED's by 5-10mA or so wont hurt em that much, overdriving them with no resistor will. LED's have a MTBF greater than 100,000 Hours (11 Years !) so overdriving them a little wont hurt

 

Could it be that the resistors supplied with the LEDs are intended for running the LEDs from 12V and not 5? What are the resistors' values?

 

Thanks for the help guys. I tested the resistors with a multimeter and determined that they were 470 ohm. I swapped my power source over to 12v and the leds are working like a champ...bright, but not hot.

The mousepad is complete, but for some stupid reason my web server isnt getting requests, even though I have the port forwarded to it. I'll work on it more tonight and post the pics of the completed mod.