Certified Bike Brat
Join Date: Jan 2011
Location: Montreal, Quebec
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
More lumens doesn't necessarily mean better lighting
Where the light goes is as important as how much light is available.
Most bicycle lights tend to be a lot like flashlights - a narrow circular beam that has a beam spread of about 15 degrees. To provide an equal amount of illumination over a 45 degree circular area would require NINE TIMES the light output - simply because that's the difference in area covered.
The problem for bike light manufacturers is vs a 10 watt 900 lumen light with a 15 degree spread, a 45 circular beam would require a 90 watt, 8,100 lumen output to provide the same level of illumination over that larger area. And battery cost and run times would be affected accordingly.
So cars went to a combination of prismatic and Fresnel lenses a long time ago to control beam spread and make it more energy efficient and more effective. Bicycle manufacturers could do the same thing if they wanted to. Spreading a beam only sidewise to cover 45 degrees would reduce the requirements from 9x to only 3x or 4x that of a 15 degree circular coverage.
This is a conventional 10 watt 900 lumen LED using a projector lens and grid to produce a 20 degree beam. Photo is taken in an unlit section of a bike path. Exposure is ISO 100, F4 and 1 second. That's 1/4 the duration normally used to post beam shots.
And this is a 40 watt 3,600 lumen array using projector lenses and Fresnel lenses to produce a 45 degree beam while still limiting the vertical spread to about 20 degrees. Exposure is ISO 100, F4 and 1 second. Lighting isn't brighter - just the coverage is wider. But the lighting IS more effective.
Street illumination with that array is pretty good even with wet pavement and the indirect stray lighting will still pick up reflective surfaces a couple blocks away.
Some people are apparently perfectly happy with a couple hundred lumens and a narrow beam - I can't imagine that myself. This is as big a change from conventional bicycle lighting as making the move from 10watt halogen bulbs to 10 watt LEDs
Last edited by Burton; 08-19-12 at 11:23 AM.