A resistor is the most common and best solution if you know the current of the LED. Get the value of the resistor using Ohm's Law (if the LED is 20 mA, you need a (5 - 3) / 0.02 ohm (100 ohm) resistor. If you don't know, you can experiment with resistor values (might waste a few LEDs), or use a costant current source (search LM317)
As one LED fails, the others will take more current and the rest of the LEDs will start to self-destruct. The reason why they take more current is this: the current-limit resistor will have been designed so that say 60mA will flow when 3 LEDs are in parallel. When one LED fails, the remaining LEDs will take 30mA each.Expert Reply: LED lights draw less power than the incandescent lights you are replacing which can cause issues. You will want to use load resistors like Load Resistor Kit for LED # DI34ZR on each light you are replacing. expert reply by: Scott S. Ask The Experts a Question >>.
So why is a resistor value such as 200 ohms commonly used when the calculations indicate 69 ohms? The easy answer is that a 200 ohm resistor is a common resistor included in many experiment kits. We want to use a common resistor if the light emitted by the LED will not noticeably decrease.
Often, a red LED's forward voltage is ~2V, a green one ~3V, and a blue one is ~3.4V, but it really does depend on the LED manufacturer and the exact frequency of the light emitted. Once you know the forward voltage of an LED, you can use Ohm's Law to calculate the resistor you need for a given power supply voltage. . 67 93 172 474 154 343 118 52