This is the LED cluster light I was thinking of building before I went ahead with the inverter lamp, and have now completed:
The LEDs were sourced from a cheap and nasty camping light, obtained from a pound store.
The LEDs were mounted on breadboard. Five suitably-cut pieces were arranged in a six-pointed star formation and the LEDs mounted at the ends, the leads soldered along the copper tracks. The large central piece has 8 LEDs, 4 each side, and the four smaller pieces have 4 each. They are arranged, electrically, as follows: ((Four in parallel), in series with (four in parallel), in series with a 39 ohm / 2 watt resistor) in parallel times three. The forward voltage drop of each device is 3.8V, so the current drawn is 3 * ((12 – 7.6) / 39) = 0.338A = 338mA. This is effectively shared between 12 series pairs, so the forward current of each diode is 28mA.
The base was obtained from a blown light bulb by carefully breaking the glass and removing the large pieces with gloves. The new lead wires were soldered to the existing solder points in the tip and at one side. The red wire you can see in the photo goes from the tip contact of the bulb to the anodes at the top of the cluster. The whole thing is held firmly together with epoxy resin; but for clarity’s sake, the picture was taken before the resin was applied.
And here it is, screwed into the fitting of the original donor lamp:
Note the power lead, with the 6.3mm. jack plug and the original switch re-fitted. The two halves are held together by interference fit pegs in the corner, and were easily separated by working a blade between them; the switch itself is single pole, and the terminals are crimped. It was simple enough to cut into one conductor, open up the original crimps with a small screwdriver and remake them afterwards by pushing down hard with a wider-bladed driver.
I’m really going to have to get hold of a candle-power meter now ….. or build one, somehow.