I am making a test set and want to use LED's and have them light up green or orange when 5 different DPDT toggle switches are in forward or backward position. I will have 4 red LED's using SPST toggle switches. The power source on the DPDT's is 12 V and the SPST's is 5 V. I want to see the LED's easily facing them head on from 3 or 4 feet away in daylight usage. What would be the best resistor and LED combination sizes to use?
Use Ohms Law to calculate your resistor, which will go in series with the LED. You need to know the value of the forward current for the LED's, then just divide that value into your supply voltage. Now, you can adjust the resistor value a bit higher for a comfortable light and not run it at it's maximum for longer life of the LED's.
Added note: You can also subtract the Forward voltage of the LED from the supply voltage and use the result as the voltage drop across the resistor which can then be calculated by dividing it by the Forward current rating of the LED. This will be a brighter illumination from the previous method above.
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