This is an easy and practical LED safety torch that can be made very cheaply. It has some distinct advantages compared with a standard incandescent bulb torch.

# It is extremely robust,

If dropped there is no need to worry about a filament breaking as with a standard incandescent bulb. With normal use they are practically indestructible.

# The LED has an extremely long life.

Typically up to 50'000- 100'000 hours of continuous use. So considering what it is used for, a lifetime.

# Extremely low power consumption.

This particular LED is rated at only 20mA. So even with the deadest of batteries and you find that your generator has packed up, you've squeezed that last spark out of the spark plug, your on the back road and it's dark. Tthis torch when plugged into the BMW auxiliary socket will fire up and give enough torch light to hopefully help find the problem or signal for assistance. And the supposedly dead battery will allow the torch to work for hours.!!!!

The torch if wanted can be made with practically any "body" and even smaller than the one I made. I turned up an aluminum tube approximately 10cm in length just to keep it at a size that is small enough to stow it away in the corner of the tool box and still large enough to be handled as a torch. But as I said it can be made of any material and size.

Just to note. This torch is not going to light up the roadside but will give enough effective reading and trouble shooting light from about 50cm.

The LED is a 10mm ultra bright white light with water clear lens

2500mcd @ 20mA 15Deg viewing angle. Max continuous 30mA Max voltage 4.0V

The resistor used is a 1/4 watt 60 Ohm.

A length of double core multi filament wire

Some sort of torch body

These LED's work from a voltage range of about 3.5 volts and an amperage of about 20mA.

Therefore we must use a drooping resistor to ensure that we don't fry the LED with too much current.

So how do we do that?

Let's assume that our battery is fully charged and gives us about 6.4 volts.( I know that we said that this torch will work with a dead battery but we may also want to use it when our battery is in good condition as well) We will set it up so that it operates at maximum efficiency at 6.4 volts.

So to find the resistor that we need is easy 6.4 (our battery voltage)-3.5 (our LED operating voltage)=2.9 (our dropped voltage) 2.9 / 0.02A (LED operating amperage)=145K ohms. Our closest resistor would be a 150-ohm resistor.

You could play around with those figures and assume that the battery will not be fully charged and that you'd like to run the LED at it's maximum amperage, say 30mA, so the resistor value will change.

Below is a resistor soldered to the + leg of the LED and the extension wires. To just add some strength and keep it sealed you can use some heat shrink.

This is a 6 volt 4Ah sealed led acid battery; it's almost completely dead.

To the same battery I've connected a 6 volt 2watt bulb. You can see that the filament just glows, certainly not enough to give effective lighting.

This is the LED torch connected to the same battery you can see how bright the LED is

I have placed a piece of white paper approximately 40 cm in front of the torch to give some kind of idea of the amount of light that these LED's can emit with very little power.

This is the complete torch and cable with auxiliary socket.