Placing a resistor in parallel is generally a bad idea. It is like making your car go slower by breaking while not releasing the gas/accelerator. To make the LED last long: Use a RED LED as there require the lowest voltage meaning the LED will still light up as the battery depletes. Use a LED with a high efficiency. Yes, you typically need a resistor for each color channel (Red, Green, and Blue) of an RGB LED to limit the current and prevent damage to the LED and other components in the circuit. RGB LEDs are composed of three individual LEDs, one for each color channel. Each color LED has a specific current rating that should not be exceeded. \$\begingroup\$ The LED strip is built to run on 2.5 A at 12Volts. That is equivalent to a resistor of 4,8 Ohms. Given that we are still supplying the thing with only 12Volts, then if you put a resistor in line with the LED strip, the resistance will go up. Less current, same voltage=lower power use. So, the WS2812 does not need a resistor on its input. Full stop. The datasheet even has an exemplary schematic without one. It's still a good idea to have one between your 5V data source and your first WS2812, simply because: These things are often used in a long chain, which can very quickly change very sharply in current draw. That means the resistor in the series combo needs to drop (9 - (2*3)) = 3 volts, and the resistor on the lone LED needs to drop (9 - 3) = 6 volts. Current is continuous through a wire, so 15mA is the current. Using those values, you use Ohm's law which is very basic. This will calculate the values for the resistor: V = IR -> R = V/I. Any particular LED will work with a precisely set power supply, but the next LED may or may not work. The resistor is a mechanism for reducing the voltage across the LED as the current increases. If the LED requires more current, then that increased current will lower the voltage across the LED. TL/DR: Use a 1kOhm resistor. Rationale: This LED cannot be used as a bicycle headlight because it is the wrong type. In order to mount an optic suitable for a headlight, ie something with a 15° beam, you need a much smaller LED, much closer to a point source. This LED is way too large, it is meant to be used in floodlights. In that case, you need a resistor in front of every LED to "take care" of the difference of your 5V supply and the 3.8V LED's forward voltage (5V - 3.8V = 1.2V), that's what all the LED-Resistor-Calculators show you. So, to make LEDs light up in series, you need to supply 20mA, independent of the number of LEDs. An LED driver does that. 882. Dec 7, 2019. #2. Many 3V LEDs are not exactly 3V, they may range a bit like 3.0-3.2V. The idea of a resistor is to limit current. Even if you match a LED exactly to a voltage, it may draw more than the LED current rating. The resistor is just a safety feature to save the battery (and LED) from a short circuit current overload. For typical green LEDs, that's usually about 2.1 V. Red LEDs are lower, and IR LEDs even lower still. Blue and white are higher, like a bit over 3 V. Let's say for sake of example you have a typical 20 mA green LED that drops 2.1 V. The battery puts out 9 V, so that leaves 9V - 2.1V = 6.9V accross the resistor in series with the LED. MYBCl.