Originally Posted by
Sixty Fiver
We are now seeing bicycle lights that are as bright as good quality car headlights... problem is that many of them are poorly built and throw light where it is not needed and this poses hazards to other road users.
Putting a car headlight on your helmet is going to get you noticed and maybe not in a good way.
I am not a fan of over regulation but the whole light race has really been grinding on me since it seems to be all about me me me and often shows a lack of consideration for those people we share the road with.
This constant worry about bicycle lights baffles me. Do you people not
look at your lights when you ride? Do you not
think about where you ride on the road? We bicyclists "share" the very, very, very right side of the road with the exception of those countries where we have to share the left side of the road. Every "bad optics" light I've owned doesn't even come close to spraying enough light over into the lane of on-coming traffic to be of any concern whatsoever. On a regular roadway, I'm no closer than 11' to 15' from the nearest car coming towards me. Light emanates from the lamp as a cone in a straight light. Unless I do something silly like suddenly turning in front of the car coming at me, there is little chance that the light from my lamp will get into that other lane.
You also have to take into account the spread of the beam. If you have a narrow spot, the intensity of the beam is higher but the spread is lower. If you have a wide flood, the intensity of the beam is lower but the spread is more. Since the beam spreads from the lamp in a cone, it's a simple math problem it calculate the amount of light per area (i.e. lux) at just about any distance. Most of the Magic Shine and their clones are floods with a 35 degree reflector. At 10m (roughly 30 feet for the metrically challenged), the area covered by the beam is 31 square meters. Solving an equation for the radius of the circle, I get a circle with a diameter of 6m but only half of that shines into the roadway. That's not enough distance for the light to get to the dividing line, much less get into the eyes an oncoming motorists who should be a few feet further over.
By using the area of the circle of light, assuming a homogenous beam (it isn't) and knowing the output of the lamp (600 lumens), I can calculate a lux for the beam. It's 19 lux which is significantly below your 40 lux lamp. The way that you can get 40 lux out of a your lamp which probably has a lower output is having a very narrow beam. Lots of light, no spread.