Turn an Incandescent Torch Bulb Into a 1W LED

G'day Everyone,

My wife bought me a WW I 'ORILUX' Officer's trench torch for my birthday, but the batteries they used are next to non-existant, and the little screw-in light bulbs that you can get (at least in my area) are either 2.5v or 6v. Can't get a 6v battery in the torch, and two 1.5v Alkaline batteries kill the 2.5v bulb fairly quickly. Also, the brightness of the 2.5v was pretty woeful. So using one of the, now dead, 2.5v bulbs I set about modifying it to run a 1w Warm White LED. This involves *no* alterations to the torch. Because I'm only using two 1.5v batteries (with a voltage just over 3v when new) the LED is less than half as bright as when they are run at their peak 3.8v 300mA, but are still three or more times as bright as the incandescent bulb, and it generates almost no heat at this low load, and doesn't need resistors. In the embedded video I made (from which I've taken stills for the text tutorial) the batteries are are quite old and down to 2.78v, but the LED is still usefully bright.

This is my first Instructable and if there are any questions, put them in the comments, and I'll try and answer them.

Parts/tools.
.Safety glasses

.Dead incandescent torch bulb

. 2 x 1.5v batteries

.1w warm white LED

.Soldering iron and solder

.Fine sand paper

.Heat shrink tubing

.Electrical tape

.Heat gun

.Scissors

.Pliers (fine nosed is better if you have them)

.Paper towel

and optional, but useful:

.Multi-meter

.‘Helping Hands’ jig with alligator clips and magnifying glass.

I bought a bag of Epistar brand, 1w, warm white, LEDs off Ebay a couple of years ago. They have a nice round phosphor dot in the middle, as opposed to the square one on some other brands, so, even focused through a lens, they have the traditional shaped pool of light. Their maximum power consumption is 3.8v and 300mA, giving 110 lumens which is extremely bright, and at this rate they generate a reasonable amount of heat and need to be mounted on a heat-sink. If, on the other hand, you run them on 3v - 3.2v then the brightness is less than half but they generate almost no heat. Bear in mind that the average incandescent bulb generates 10 lumens per Watt, so the LED is still around 4x brighter at this voltage.

Now I’m happy to admit that my knowledge of all the finer details of current delivery for LEDs is very small, but I’ve mucked about with this set up in my torch for about a year with no problems. We light up our toilet with two of these LEDs, in series with no resistors, from a 6v gel acid battery (so only about 3v per LED) and they have served us for around 3 years so far. Even though those two LEDs put together are not as bright as one on maximum power, they still give a 40w light globe a run for it’s money for brightness. It *is* a very small room with white walls that reflect well.

Onward!

Wrap the bulb in paper towel and carefully break the glass (photo 1). I used pliers but a careful tap with a hammer will do (photo 2). Use pliers to crunch off any rough edges of glass left behind (photo 4).

Cut a short length of heat shrink tubing and fit it around the top edge of the bulb to insulate the bare metal of the screw-in base from the two wires that hold the filament (photo 1). Heat this up with the heat gun from the bottom of the bulb so that the tubing will grip around the metal base. If you heat it up from on top (where the glass used to be), as the tubing shrinks it will pull itself off the bulb. In the second photo you can see the tubing starting to grip around the metal base of the 'bulb'; the heat gun is just off camera to the lower right.

It should now look something like this.

Snip off the remains of the tiny filament (photo 1), and bend the support wires out sideways (photo 2). Then sand the ends of the wires nice and shiny (photo 3).

Clean the wires, and the contacts on the LED with Methylated Spirits (De-natured Alcohol) (photo 1). And solder the ends of the bulb wires and the *top* faces of the LED’s contacts (photos 2 & 3).

Also clean the little heatsink under the LED with the Metho, so that you can stick a square of electrical tape over it to safe guard against the contacts shorting out on it (photo 1). Then fold the contacts under the LED (photo 2).

Check your torch’s electrical polarity. The way I have the batteries set up in my torch means that the base contact is ‘negative’. Find which wire on the ‘bulb’ is connected to the base contact, and which one to the metal body. In this case the lower wire in the second photo is connected to the base contact, and is ‘negative’.

LEDs only work with the power running in one direction. One of the two contacts on the LED will have something different to identify it as the + contact. You need to solder this one to the wire on the ‘bulb’ that will connect with the torch’s +ve. In the first photo I’m soldering the -ve and, in the second photo, the +ve. The third photo shows testing the circuit to make sure the LED is working.

Then put another piece of heat shrink around the LED in order to strengthen the unit, and stop the contacts from shorting out on the torch’s reflector (which in this case carries the +ve current). While the heat shrink is still warm and soft, make sure the LED is set up nicely square with the bulb base. Once cool, this will be quite secure. Then test the circuit again.

I put some heat shrink tubing over the jaws of a pair of pliers to help me screw in the ‘LED/bulb’ and to protect the torch’s reflector (photo 1). When you start feeling tension as you're screwing it in, make sure the pliers are gripping the base of the 'bulb' and not the LED as this might break the wires (photo 2). The first time I fitted it the LED wouldn’t light up, and it was because I’d made the original piece of heat shrink too long, interrupting the circuit (photo3). So I carefully cut off about 1/2 the length of the tube (but still leaving enough for it to firmly grip the bulb’s base) (photo4).

Success. The LED, of course, only sends light in a forward hemisphere, whereas an incandescent bulb sends light throughout the full sphere. Therefore different reflectors and lenses, or absence of them, will give different results. This WW1 Trench torch uses a ‘bull’s eye’ lens and is very good at collecting the LED’s light and focusing it forward, and is several times brighter than the original bulb, and is more responsive for the Morse Code function.

Have fun!

Cheers

Duncan