What this instructable does:
Take a regular PR 2 bulb with a P13.5s base (i.e. those most commonly in torchlight), reuse the base and insert 3 x 5mm diameter white LEDs. See image of end result below.
The shortcut to this project is to go into a shop and buy one of these. But hey, what's the fun in that when you can make your own!
Step 1: Removing the glass bulb
The glass bulb is fused to the metal base with a clay-like cement, and should crumble easily. Once the bulb is removed, use a mini screwdriver scrape the metal base clean. The internal surface wall of the base has to be electrically conductive.
What's left is seen in the image below.
Step 2: Desoldering the remnant of the glass bulb from the base
Step 3: Shaping the legs of LED
What you need to do is bend the legs, solder the anodes together (that's the positive polarity leg, the longer one, or see http://en.wikipedia.org/wiki/LED ). A bit of tape would help securing them together while you do the soldering.
Next, fold the cathode legs into a u-shape, about 7mm long, these have to make contact with the internal wall of the metal base.
Once you have done that, what you have is something like the image below.
Insert this into the metal base, through the hole at the end, solder and cut away the protruding excess.
Step 4: An important final note
When using a white LED, the easiest method of driving these, is a connection in series, with a shunt resistor. Working on typical values for a 5mm white LED.
For 3 battery cell, between 3.6V to 4.5v, depending whether you're using alkaline or rechargeables, assuming a nominal of 4V, with the white LED operating voltage and current at 3.3V, 30mA respectively, (4 - 3.3)/30e-3 , a 22 ohm resistor will do.
For 4 battery cell, between 4.8V to 6V, assuming a nominal of 5.4V, with the same typical values for a white LED, (5.4 - 3.3)/30e-3, a 68 ohm resistor will do.
A direct placement of the resistor in the metal base could save you more hassle.