How can I find the right resistor to make 50% brightness in an led? I know how to find the right resistor to get the brightest but I'm wanting to find the perfect middle.
Question about resistors and LEDs
ledresistors
Related Solutions
Or a decade counter: (you are free to arrange the ten LEDs in a circle if you wish.)
If you want to power all of the LEDs in series, you only need a single current-limiting resistor for the entire string. However, your power supply voltage must be at least the sum of all of the LEDs' forward voltages. If that's not convenient for your application, you should divide them up into separate strings and connect the strings in parallel. Importantly, each string should have it's own current-limiting resistor.
Best Answer
Chances are that for an perceived "half as bright" LED you'll need to increase the resistor by around (5:1), which will yield around 20% of the lumens.
Compare the popular North American auto tail light bulb the 1157, which has two filaments- brake and running light. The filaments are about 28W and about 8W, but the lumens are about 10:1 (402 vs. 38 lumens). Yet the brake lights are not perceived as ten times brighter- maybe 3 times.
This is because your eye has approximately a logarithmic response over some range, so in fact a difference of 20% or 25% in lumens is barely perceived.