I did a bit of searching… found that the brightest red LEDs are on the order of 50 lumens per watt, which is about five times what a 25W (1157 style) can reach. I ordered up some of them and built a prototype circuit using five LEDs and a LM3409 constant current controller. The LEDs I used have a nominal rated current of 350 mA, which corresponds to about 0.8 watts each, so this array is currently using 4W of electrical power in ‘brake’ mode, and about 1 watt in ‘taillight’ mode. The LEDs are arranged on a 0.9 inch circle, more-or-less centered on the turn signal lens (just for testing purposes).
The problem with this is that the light kind of gets washed out due to the limited dynamic range of the camera. From further away and at an angle you can still see that the LED array (on top) easily outshines the incandescent bulb.
An interesting comparison is what gets projected onto the inside of the garage door.
The left side brakelight on my Tiger (on the right in the bottom picture) has the earlier internal-screw style lens with the circular pattern in front of the bulb – but you can see that it doesn’t actually throw the light anywhere of significance. The right side brakelight has the outside-screw style lens with the vertical bars, and it spreads the light so much you can hardly see the illumination on the door. The LEDs, however, make a nice light show on the door.
So this is with five LEDs… I’d considered making an 8-LED array but I think that would almost be overkill. It would be more effective to rewire the taillights to use both the upper and lower bulbs for the tail/brake function and keep only the top for the direction indication (this won’t work for Tigers configured with amber upper lenses). So maybe people should have the option.
Unfortunately I somehow gapped out completely on the cost of this thing. My cost on the LEDs is about $3 each, the regulation circuit came in at about $9 and the PCB will still be about $6 minimum. So I’m in for $30 each in parts cost for a 5 LED light… that means the assembled cost is going to have to be on the order of $50. However, if I were to spend $100 and save my car getting rear-ended it’s cheap.