For those out there who are starting to consider night riding...
From
www.recumbentblog.com: August 05, 2007
Shedding a Little Light on Lights If I had to, I could gauge the time of year by how long I run my bike lights in the morning. During the summer I only turn them on for the first half hour of my daily ride. But as we pass the summer solstice and make the long, sad slide toward the dark of winter, the lights stay on longer and longer. By the time winter has arrived in earnest, my entire ride is enveloped in a blanket of murky darkness. Even though it's only August, I can already detect the change of seasons coming, and the darker mornings have started me thinking about lighting systems again.
In the process of comparing lights from various manufacturers, one thing that has always been frustrating is the lack of a standard method for measuring light output. Some manufacturers use the "candlepower" measurement, while others use "lumens", and yet others only state wattage and skip light output altogether. I'm no authority on lighting, but in my research I've discovered a few things that might prove useful to my fellow laypeople when they're sorting through the jargon.
Candlepower
Candlepower is a common measure of light, but it's not particularly useful for describing the brightness of a bicycle light. Candlepower only describes the single brightest point in a beam pattern and doesn't account for the remaining light in the beam. It's not unusual for two lighting systems to produce vastly different amounts of light and share the same candlepower rating.
Lumens
Lumens are a measure of the total amount of light in a beam pattern. Lumen ratings are probably more useful than candlepower ratings when comparing bicycle lights. The quality and design of the optics in a lighthead, along with the intensity of the light source, work together to produce the total light output that is captured as a lumen measurement.
Watts
Watts are defined as "the absolute meter-kilogram-second unit of power equal to the work done at the rate of one joule per second or to the power produced by a current of one ampere across a potential difference of one volt : 1/746 horsepower." Huh? I have no idea what that means, but from experience I can surmise that watts are more about power and not so much about light. I've owned high-watt lighting systems that looked good on paper but were only average on the road, and I've owned better designed low-watt systems that were more effective in real world conditions.
Beam Patterns
Beam patterns are a big deal and are hard to quantify. Some lights have high lumen ratings but spill off massive amounts of light into the trees and night sky (and blind oncoming vehicle operators). Others have more efficient, focused beams that are dim at the bottom (where they hit the road at near distance), and grow progressively brighter towards the top for reaching far down the road. The best of these have an abrupt cutoff at the top of the beam, similar to high-quality automotive low-beams.
When shopping lighting systems remember that numbers on a spec sheet only tell part of the story. Lumen measurements are more meaningful than candlepower measurements, but beam patterns are king and can't be quantified on paper
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Lighting the night -- headlight comparisons (Read 4546 times)
