Measuring exterior light output

This page has information useful for those interested in converting their front and rear exterior lighting from conventional incandescent light bulb to LED. Do so only if the light output from the LED is comparable to the original incandescent light bulbs.

Note that LED in continuous on mode (tail light or brake light on for long period of time) without sufficient heat sinking may suffer a reduction in light output. The reflector in a housing for an incandescent light bulb is not designed to reflect light optimally for multiple LEDs not located where a bulb filament would be.

I used a light meter for light output measurement. The lux measurements were taken during a cloudy moon-less night. With the vehicle exterior light off, the light meter reading was zero. The light output reading was taken on axis at both the right and left side, at a distance of about 1 yard / 36 inches / 0.91 metre, on axis as much as possible, varying by about a 1 foot / 12 inches / 30 centimetres diameter cicle to capture the highest output. The best side is reported.

BMW E90 Depo Blackline tail light:

Parking light, 10 lux; with brake light on, 108 lux.

BMW E60 LCI LED tail light:

Parking light, 17 lux; with brake light on, 108 lux.

BMW E60 LCI Xenon headlight with MTEC v3 CREE LED 26-watt angel eyes or corona ring light:

With parking light, 216 lux; without parking light, 202 lux (headlight off in both cases).

Manufacturer LED light output ratings (lumens or lux) are meaningless by themselves. The LED light output measurement should be measured when installed in the reflector housing. It is this application that one will discover that most LED do not produce as much light as the conventional incandescent bulb. LED marketed as CAN bus error free will still trigger a lamp malfunction message in most modern BMW vehicles, due to their sensitive lamp electrical load monitoring system.