Thursday, February 07, 2008

Lumotec Light Problems and Diagnosis

I've been using the Lumotec N and Lumotec Schmidt Switch headlights for the last 3 years, but have had really poor reliability with them (so did my brother). In the cases of most of the failure, it seemed as though all that was needed to destroy the lights was a sharp knock. Late last year, my 18-month new Lumotec N failed again. But a sharp jiggle to the wire brought it back, so I thought nothing of it. But when I moved the light over to the new bike, the light once again failed.

So this morning, I rode over to Pardo's house and we took the light apart and tried to fix it. The first observation Pardo made was that there was no strain relief at all on any of the wires. This made the prime suspect a broken wire. We fiddled about, but the light appeared to work once the casing was off. So we decided to call it a day and reinstalled the light. I then took the bulb out to clean it before riding off and it immediately failed. On examination, the bulb is held against a negative contact spring by the holder, and the positive contact is a spring. The positive contact is fine, but the negative contact had become corroded. A cleaning, however, did not solve the problem, so I suggested using tweezers to pull the contact out towards the bulb. That solved the problem, and the light is now reliable.

My conclusion is that the Lumotecs are not very well-engineered. According to Pardo, adding strain relief (which is routinely done, for instance, for objects such as cell phone chargers) adds a few cents at most. The contact spring should be stronger so that a year of jiggling and rain riding does not destroy it or cause intermittent failure. But my guess is the majority of these lights outlast the year warranty, so the manufacturers have no incentive to fix these problems.
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