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8.9 Lighting Systems




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This article is from the Misc Bicycles FAQs, by various authors.

8.9 Lighting Systems

From: wittenberg@zendia.enet.dec.com

There are some interesting and helpful ideas in the original article,
and I'm adding my comments here. I commute 12 miles each way on dark,
unlit streets with very little traffic. I would change my lighting
system somewhat if I saw more traffic.

|> 1) Quartz-halogen headlight of 12 to 55 watts (legal maximum). Mediocre
|> systems have lights of less than 12 watts, while totally inadequate systems
|> drop below six watts.

A little strong, but close. When I had a Brite Lite 2.4 W bulb, every
car that I passed dimmed its lights for me proving that I was visible,
but I couldn't see well enough to ride at a decent clip. When I
upgraded to 2 Brite Lite 4 W headlights, I could ride up to 14 or 15
mph comfortably. I just upgraded the headlights to 6W each, and
that's very good. I wish I had another helmet-mounted light for
lighting the inside of curves, which is still a problem.

|> 2) High intensity rear strobe light. A piercing strobe, visible from
|> both the rear and sides, commands the attention of oblivious motorists.
|> Poor systems have a small, barely visible taillight.

A strobe lets people know you're there, but it doesn't give them a
good idea of exactly where you are. Depth perception of strobes is
pretty bad, so you want to also have a steady light. I use a Belt
Beacon as a strobe, and a standard Brite Lite taillight. I also have
a Vista Lite, which is a new taillight that looks sort of like a
reflector, and has 3 bright LEDs which flash. (It was recently
discussed here.) That, and reflective tape everywhere (especially low
down, on the bottom of my rear fender, where car headlights are aimed)
makes me very visible.

I'd like to make a constantly on taillight from the LEDs used in the
Vista Lite. It would be brighter and use less power than the
taillight I have now. As soon as I figure out where to get the LEDs,
and how to mount them I'll do this and let you know how it works.


|> 3) Mounting of lights. The headlight should be attached to the headset-
|> mounted front reflector bracket found on most bicycles. The handlebar
|> type mount is almost as good. Helmet mounted light, while useful for
|> roadside repairs, do not illuminate the road ahead when you are in the
|> proper riding position on a bicycle with drop handlebars. The best location
|> for a rear light is at the motorists' eye level (most tal lights mount
|> too low to be useful).

I mount my headlights on my fork. There are several advantages over
the more standard handlebar mount. First, they don't put light in my
eyes. Secondly, by putting them low, they let road bumps to cast
shadows, which makes it easier to see them. I use either the U-bolts
for a blackburn low-rider rack or standard U-bolts mounted on the
fork. Two headlights has the further advantage that if one of them
goes out you don't have to try to replace a small bulb in the dark.

|> 4) Battery capacity. For high power lights, you need a gelled electrolyte
|> battery from 2.6 AH (1.8 hours with 14watt headlamp and 3 watt strobe)
|> to 6.5 AH (4.6 hours). These are of reasonable weight and cost.

This is very optimistic. Battery AH are rated when drawing current
slowly (10 hour discharge rate), and at 70 F. Drawing a battery down
faster and at a lower temperature both decrease the power available.
One rule of thumb is to expect half the rated energy from a battery
used in bike lights.

Despite my differences with this design, I'll get a copy of his plans
to see what else I can learn. He seems to have some good ideas in
there.


 

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