DIY Maglite LED

Disassemble your current flashlight and remove the bulb. For example, assuming you have a 4-D-cell battery, with each battery having a voltage of 1.5 V, the total will be 6 V.

Select a white-light replacement LED. You'll need to consider the size of the LED, the light output and the current requirement, which determine the heat dissipation. For example, use a 350-milliamp-rated LED with a stated efficacy of 50 lumens per watt.

Select a desired drive current. For a longer service life and a lower operating temperature, you should select an operating current well under the specified maximum current. For the chosen example, select an operating current of 100 milliamps.

Calculate the value of a current-limiting resistor. The current-limiting resistor protects the LED from damage and extends the lifetime of the LED. You'll need the forward voltage drop, listed on the product datasheet. The resistor value is given by the equation:

resistance = (supply voltage - voltage drop) / drive current.

For example, if the forward voltage is 2.1 volts, the supply voltage is 6 V, and the current desired is 100 mAmps, the resistor is

resistance = (6 - 2.1) / .100 = 39 ohms.

Solder the current-limiting resistor to one lead of the LED, say, the anode.

Connect the positive voltage lead to the opposite lead of the resistor, and the negative lead to the LED cathode.

Fit the LED into the reflector bulb housing. Package sizes and formats vary, so there's no general rule, but using RTV will help you mount the LED.

Reassemble the flashlight.