What's an LED? Simply put, a Light Emitting Diode is an electronic component (a semiconductor diode) that emits light when an electric current passes through it.)

LEDs are becoming more and more popular for a number of reasons

So how do we use LEDs?
The "classic" LED circuit uses a power source, the LED and another electronic component, a resistor. The purpose of the resistor is to limit the current through the LED to ensure that it does not overheat and burn up. The value of this resistor is calculated using Ohm's Law:
Resistance= Voltage / Current



Now, this is a simple, inexpensive circuit and under the right circumstances it can work just fine. But LEDs work best with a stable current supply and using this circuit means that the resistor value must be recalculated if the power supply changes or the number or type of LEDs change.
A better solution is a constant-current regulator that will supply the same amount of current even if the power supply voltage changes or we decide to add a few more LEDs or use say, a red LED instead of a white one.

The output current is calculated thus: I= Vreg/R1. e.g., for a 7805 5V regulator and a 100 ohm resistor, the output current is 5/100= 0.05A = 50mA

One potential problem with the circuits above is that they are inefficient at higher voltages. If we are using, say a 12V power supply with an LED that only requires 3.6 volts, but runs on 350mA, then the power used by the constant current supply or resistor is fairly high. The power would be (12 - 3.6) x .35 = 2.9 Watts! That's quite a bit of power and the ccs or resistor will get fairly hot.

One solution to this is to use what is known as Pulse Width Modulation (PWM). PWM sends short pulses of current to the LED, but the pulses are spaced far enough apart that the average voltage is less than the original voltage. For example: if a 12V supply is switched on and off at a 50% rate (equal periods of ON and OFF), the average voltage will be 50% of 12V, or 6V. This method of voltage reduction is efficient and does not generate heat. Our Light Explosion works by sending extremely short, widely spaced pulses to a high power LED to create very bright flashes.