How to reduce the voltage on the LEDs from 5v to 3.5v?

Question

LEDs

I bought a keyboard with a blue backlight - it has 10 LEDs on a long bar - I need to replace them with other LEDs - but knowing that the USB outputs 5v I can’t find the LEDs for 5v - I found only 3.5v - the question is: how can I lower the voltage inside the keyboard? and how can you solder the LEDs so that they do not burn out (I read somewhere that they distribute voltage among themselves)?

Answer 1

Look at how your diodes are connected on the bar, perhaps there are already resistors there or they are connected according to a different scheme.
It is correct to turn on each of the LEDs through its own current-limiting resistor - for 10 diodes 10 resistors. Resistance can be calculated using any calculator or Ohm's law formula. In simple designs, there is a parallel connection of LEDs with a common current limiter (resistor), but due to the spread of diode parameters, the currents through them will also differ and may exceed the allowable ones. But if you reduce the total current by a factor of 1.5-2 from the nominal, the design will last longer.