Workshop: LED Torch Conversion
High powered LEDs (light emitting diodes) are usually much more efficient than an ordinary incandescent torch bulb, and replacing a bulb with an LED will give you a longer burning, brighter light.
Unfortunately it isn’t just a matter of directly swapping a bulb for an LED, because the voltage required by an LED is generally less than required by a bulb. Directly swapping a bulb with an LED will probably result in a broken LED, but you can sometimes get around the voltage problem by switching from ordinary batteries to rechargeable cells.
Rechargeable batteries have a lower voltage than disposable batteries (1.2v versus 1.5v). The operating voltage of most 1-5 watt Ultrabright LEDs is about 3.5v, so if you have a torch that uses 3 batteries, you can replace the bulb by soldering an LED in it’s place, and use three 1.2v rechargeable cells to give you 3.6 volts.
If your torch uses more than four batteries, you can still switch to using rechargeable cells, but replace one of the cells with a piece of appropriately sized metal bar. The metal bar fills the space left by the missing battery, and will carry the current just like a piece of wire.
You can also use more than one LED to increase brightness. Connecting LEDs in series means that you can multiply up the input voltage, too. Four 3.5v 3w LEDs in series will need about 14 volts, but will also give out four times the amount of heat and light as a single LED.
To give some idea of the power difference between LED and incandescent bulbs: A 5 watt LED will give out (very) roughly the same amount of light as a 35 watt incandescent bulb. You can use special lenses to focus the light from an LED into a tight beam, giving a level of illumination far in excess of that provided by an ordinary bulb.