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Tuesday, November 27, 2012

2013 Bike Lights Shootout – Mtbr Lumen Tests [MTBR]

Bike light manufacturers can put any ‘lumens rating’ on their product that they want. There is no governing body out there that states that they have to measure or be truthful about what they claim their light output to be. What many of them do is read the LED spec that they are using, get that LED’s max rating and multiply by the number of them that they are using and voila, magic lumen number.
The problem is that number is a best case and impossible number. The real output is somewhere below that. The reasons for lower output are:
  • Heat dissipation – as the LED gets hot, it gets dimmer to protect itself
  • Power source – if the power source is not at the perfect voltage, it gets dimmer
  • Reflector light loss – the mirrors on glass on a light will result in some light loss
  • LED Binning – all LEDs at birth are sorted for their brightness. So all LEDs of the same model are not equal
That’s why Mtbr works so hard to demystify LED output.  The ultimate test is using an integrating sphere to measure light output. This piece of equipment costs about $20,000- $100,000 to purchase and requires a trained technician to operate. This year, Mtbr is using the integrating sphere of Light and Motion and Lezyne to measure lumen output.  We are present during all measurements and we will cross-check their work with each other.
Lumen measuring process using an integrating sphere with Chris McCaslin.

As you can see, it is not a simple process and that is why so many light manufacturers do not measure their output.  There are very few independent labs around this country too that can do this work.
We realize of course that Light and Motion is a manufacturer and they are testing competitors’ lights. But we have evaluated their process and were present during testing. Furthermore, we are double-sourcing this year by testing at another manufacturer called Lezyne and cross-checking their work. We have already compared four lights that they each measured and the results match up within 1-2%. Finally, this is just a piece of our lights testing and is supplemented by our own Mtbr Lux lab testing and light beam image data.

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