Sunday, July 19, 2009

Increasing Brigitta's Tailight's Lumen Output

Brigitta, my 1987 R80 Beemer, came into my possession with a 5 watt tail light bulb. It was dim, it's light hardly visible in bright sunlight, at least to me while standing 10-20 feet to the rear of the motorcycle.

The tail light with the 5W Bulb, afternoon sun hitting the rear of the motorcycle directly

As a stopgap, I mounted an 12 LED stoplight, wired to be on continuously while the ignition was on. I felt safer.

Recently, half of the LEDs quit working and so I revisited the light output limitations on the R80.

Yesterday, I replaced the taillight bulb with a Sylvania Type 97 13.5V 9.3W bulb from the auto parts store. The light was yellower but seemed to be a bit brighter with the red plastic taillight housing back on.

Today, I rolled Brigitta out on the cul-de-sac, walked back about 20 ft and was disappointed with the perceived light output of the new bulb. Off to the auto parts store again, did some more looking around and found a Sylvania Type 105 12.8V 12.8W bulb.

I replaced the 9.3W with the 12.8W and was pleased to see I could actually see the tail light illuminated from 20 feet away. My only remaining concern now is heat output from this new bulb, will have to monitor over time.

The tail light with the 12.8w bulb, I could see a difference with my eyes, my camera...not so much

Did some research to validate my assumption that more wattage = more light output.

I found the following excerpt on Wattage is the amount of electricity needed to light the bulb. The higher the wattage is, the brighter the light will be. LINK

Another link stated incandescent bulbs put out 7-24 Lumens per Watt. Which if you do the math, it boils down to more watts = more lumens = more perceived light.

So, taking the arbitrary value of 7 from the above statement, my original 5W bulb was putting out 35 Lumens, my new 12.8W bulb is probably putting out 89.6 Lumens. So about 2.56 times more light!

No computers, local area networks or fancy electronics on the airhead, so I don't think introducing this higher wattage bulb will affect anything on Brigitta except a bit more power drain which I'll monitor via the voltmeter.


Jack Riepe said...

Dear Charlie6 (Domingo):

The light output on my 1995 BMW K75 was equally annoying. I made several mofifications that have worked well for me.

However, I do not think that the tailight output during the day is an effective deterrant to getting rear-ended. I did think the dim "caboose" style lantern light this fixture threw off at night was not quite sufficient.

In taking the lens off, I discovered two empty chambers behind the red plastic. These now house 16 brilliant red LEDS that flash like crazy when the brakes are applied. I have also added a black metal license plate bracket that has 16 red LEDs on top and another 16 on the bottom. These light up at 50% power as running lights, and come on at a steady 100% when thr brakes are applied. Heat is not a consideration as the flashing LEDS are purely intermittant while the license plate bracket lights are external.

The internal flashing LEDS are illegal. They are supposed to stop flashing after 5 seconds. So what? I think they are safer this way.

I am running Motolights on the front.

Fondest regards,
Jack "reep" Toad
Twisted Roads

Charlie6 said...


I've the flashing LED pods on the underside of the 1150RT's brakelight housing....they flash three seconds after my main brake light flashes several times and then remain on.....the led's continue to flash so long as I hold the brakes. I don't think they're illegal here in CO since I've had cops sit right behind me at lights with no issues.

I am, considering some options similar to yours for the you know of this site:

irondad said...

So what you're saying is that you're trying to turn Brigitta into a firefly?

I agree that being visible is important. We can do it with gear, too, remember. Such as my Hi-Viz.

Pay no attention to Jack. He might like to flash his ass all over town, but that doesn't mean it's either legal or tasteful!