This post describes the modification of LEDs to optimise their role as a light source for the map reading lights in the dome fittings on a BMW E90. It is a low cost and easy modification to complete. Just basic soldering skills are required.
Having recently purchased an E90, I decided to tweak it a little.
I purchased a set of LEDs to replace the interior incandescents.
The LEDs supplied were all OK but the T10 LEDs weren't really suitable for the map reading. The LEDs fitted but most of the light was going in the wrong direction.
I brought some T10 LEDs shown in the picture. Here the standard lamp and one of the unmodified LEDs are fitted into the bayonet holders. Note that the LED isn't tall enough to fit in the map light.
As supplied, they weren't really suitable for the map lights because they point the wrong way. That was OK because I brought these with the intention of modifying them.
The LEDs are fitted to a small board that is soldered to second board that fits in the lamp socket. I unsoldered the boards and rejoined them using strips of copper. The copper was 0.8mm by 2mm.
The strips were bent so the LED boards were tilted 35 degrees. This matches the angle of the dome fitting.
The result of the modifications were a set of four LEDs with a 35 degree tilt.
The next part is the installation.
The map reading lights have a clear plastic window that makes it impossible to remove the lamps from below.
Even if the windows weren't there, the lamps would be extremely difficult to remove.
The window and black surround cannot be removed from below. They are held in with plastic tabs.
The easiest and only way that I could replace the lamps was to remove dome light units.
The rear dome unit is removed by depressing the two spring clips on the rear edge with a trim tool.
The front dome light has similar springs along the front edge but these seem to be impossible to remove in the same way the rear dome tabs are depressed.
I pressed the front springs by removing the inboard sun shade brackets and pulling the roof liner down just enough to get my hand to the springs from above.
The T10 lamps are held in a bayonet type holder. The LEDs can only be fitted one way round.
On the rear dome light, positive needs to be forward. On the front dome light, positive needs to be at the rear. This means that left and right LEDs are required. The direction of tilt matters. I found out the hard way that the +/- symbols on the LED boards cannot be relied upon.
Here is what the LED looks like when it is fitted to the map light. You can also see a different type of T10 LED used in the central dome light. The modified LEDs now point in exactly the right angle to maximize useful light.
It is difficult to quantify just how bright the LEDs are.
I can look at the incandescent lamps but the LEDs are too bright to look at directly.
They are significantly brighter than the factory lamps.
The modified LEDs worked very well. The light is bright and directional. There is minimal light spill to annoy the driver.
I used the map lights on previous BMWs. I expect to use them on the E90. The LEDs are significantly better than the incandescent lamps.