Martin Lund commented < If I recall (someone correct me please) front bike lights need to legally "be visible from x-distance" rather than "light the path for x-distance.">
Martin is correct regarding the law (your white front light needs to be visible to drivers, bicyclists, pedestrians from a distance of 500 feet). We should want to not only be visible to others, however, we should also be concerned about being able to see the road far enough ahead of us to be able to recognize hazards and react in time to avoid them. How far ahead should we want to be able to see? Ask your self these questions, then put the numbers together. (1) how fast are you typically traveling? (2) How long would it take you to brake to a stop at that speed? (3) Before starting to brake, how long will it take you to recognize a situation where you have to stop or avoid a hazard and start slowing down / take evasive actions? The sum of braking distance and reaction time is your stopping distance, and how far ahead you want your front light to be able to illuminate the road/path. I have some tables from John Forester and John Allen on bicycle stopping distances at different deceleration rates. According to this information, deceleration of 0.6 G is considered the limit a bicycle can achieve before rear wheel lift off and bicyclist header. A trained bicyclist is considered to be able to achieve 0.5 G deceleration, while 0.4 G would be typical of a novice bicyclist. Using the rear brake only results in about 0.3 G if the rear wheel is not skidding, less if skidding. Let's take a best case scenario. An experienced bicyclist able to achieve 0.5 G deceleration, riding on a good, hard, dry surface, traveling at 15 miles per hour. Braking distance for 15 mph at 0.5G is 15.1 feet. In terms of reaction time, tables from the 1980's used .75 seconds. Tables I have seen more recently use 1 to 2 seconds. In 1 second at 15 mph you travel 22 feet. Thus at 15 miles per hour with a 1 second reaction time you need a light that lets you see at least about 40 feet ahead of you. If you can only see 20 feet ahead of you, you should slow down to 10 miles per hour to be safe. If you are traveling 20 mph get the best light available (56 feet braking plus 1 sec reaction time). Arthur Arthur Ross, Pedestrian-Bicycle Coordinator City of Madison Traffic Engineering Division 215 Martin Luther King, Jr. Blvd., Suite 100 PO Box 2986 Madison, WI 53701-2986 608/266-6225 -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of John Martin Sent: Thursday, December 11, 2008 12:19 PM To: Eric Westhagen Cc: Meiers, Steve; BikiesSubmissions Subject: Re: [Bikies] Finding opportunity from crisis? (Bikie attack) Topic: bike lights I agree with Eric about the cost of "cheap" bike lights. They used to be a pain because the batteries would drain quickly, but with LEDs, even the cheap ones seem to be getting expensive. My question is whether bikes actually need to be "focused" and "white." In my experience, the "cheap" LED lights offer next to nothing in terms of helping me see where I'm going. If anything, they're distracting. What I want from them is that cars see me from the front, so I'd rather have a bright unfocused light that flashes in all directions (except at my eyes). So, are there cheap *unfocused* front lights? Any recommendations? On Dec 11, 2008, at 12:05 PM, Eric Westhagen wrote: > We have discussed bike lights from all sides in previous years. And > nobody should venture out at dusk or later without a red light for > their own protection. But the lack of a focused white light seems > more of a question as far as bike to bike accidents are concerned, > and these white lights seem not as cheap as has been implied here. > Maybe there are cheap white lights, but I have not seen them myself. > I do know that my model of light, the Cateye Opti-cube is a $30-$40 > light, depending on where one buys it. Are there actually cheap > focused lights for sale at Madison bike shops? My Cateye, cost $30 > something at a Seattle bike shop and it was in the $40 range listed > "on line." Before one promotes white lights at a give away status, > some cheaper source of reliable, well focused lights must be found. > Does anybody have a suggestion? > > Eric Westhagen _______________________________________________ Bikies mailing list [email protected] http://lists.danenet.org/listinfo.cgi/bikies-danenet.org _______________________________________________ Bikies mailing list [email protected] http://lists.danenet.org/listinfo.cgi/bikies-danenet.org
