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Ultra-Bright Green 5mm LED 5000 mcd
Also I have noticed that there are 1/4 watt, 1 watt, and 3 watt resistors. Does the wattage difference affect the brightness of an led in a 12v-14v setting? Which one would i need for use in a car?
No, the resistor wattage will not affect brightness. The wattage rating on a resistor tells how many watts of electricity it can dissipate into heat safely (without catching on fire).Use the "LED Wizard" shown on the product page and input your design. The top line in the solution should say "each ___ohm resistor dissipates ___mW". This 2nd number is how many watts of energy the resistor is going to be eating up. So make sure your resistor can dissipate more than that many watts.So, the simplest set up, 1 LED, operating at a max of 30ma @ 15VDC, would need a 390 ohm resistor rated to dissipate up to 351 mW of energy. So, a 1/2 ohm resistor would be adequate, and 1ohm would be prudent in this application.As you add more LED's in series, the wattage requirements for your resistor will drop, since each diode will be dissipating some of that energy as light.
Date published: 2012-03-29
If i were to use an led in my car what resister value would I need. I'm thinking 350ma-400ma range depending on the forward voltage and average forward current. Example for this led would be 12.6v-3.5=9.1 /20ma=455ma for resistor. Would this be correct and should I round up the value.
LEDs are pretty forgiving. It also depends if you want it bright or dim. Dimmer can make an LED last forever. It is not important what the operating current is as long as you don't exceed the max rating, and you have a DVM with current input to monitor it while you experiment.Im not sure about your math: most LEDs are 3V devices @ 20-30ma without a dropping resistor. At 5V, you should use a 100 ohm reisitor minimum [50ma], up to 500 ohm [10ma] depending on how bright you want it [ohms law: 5/100=50, 5 divided by 100 = 50].For automotive use, you want to plan on 10-14.8V [15V max] because the voltage fluctuates a lot in a car system. So you would start with a 300 ohm resistor [2200ma @ 15V=bright], up to 2K [7.5ma=dim] to throttle it down some, or somewhere in between =1K to allow a wide range of voltage to be tolerated by the LED.These high-bright LEDs can go up to 70ma so even 80 ohms @ 5V, and 220 ohm @ 15V would work for MAX brightness.To learn how this works, set up on your bench using a 5K ohm potentiometer and goof around with it, measuring the current thru a DVM. Have fun!
Date published: 2012-03-28