First let’s look at the characteristics of LEDs. This chart shows the voltage and current characteristics of two typical LEDs from the same supplier. Notice that the voltage drop across each LED at a given current is not consistent from device to device. Also note that the output illumination from the LEDs is consistent with respect to current. This helps us determine how to drive the LEDs. If the LEDs are driven in parallel with the same voltage across both devices, one of the devices would be much brighter than the other one.