The good news: Thanks to LEDs, bike lights are getting brighter, cheaper, lighter, longer running, and smaller every year.
The bad new: Thanks to LEDs, bike lights are getting smaller every year.
Have you noticed? With the latest crop of high-power LEDs, it seems like manufacturers have figured out that they can pack all their lumens into a tiny little "bulb" surrounded by a nickel-sized lens/reflector. It looks great from the saddle, when you're lighting up road signs from a mile away. But I'm not entirely convinced it's a great thing for a commuter sharing the road with inattentive drivers. When other riders approach me with one of these new micro-lights, it looks like they've taped laser pointers to their bars: All power, no spillover. The lumens aren't wasted from the rider's perspective, but they also aren't doing much good for anyone approaching the rider from an angle.
To defeat this problem, I've taken to mounting up my long-ago-discontinued Planet Bike 1-watt Super Spot for my commute instead of the more modern, brighter, and focused Blaze series (you can see beam comparisons in my critically-disdained "man in a dark bathroom" post). As far as I can tell, the Super Spot is an even older halogen light with its halogen bulb swapped out for an LED -- same case, same lens, same reflector. It makes a beam like the antique Schwinn-approved generator light on my grandparents' old tandem: weirdly striped, not terribly bright, but -- here's the kicker -- incredibly wide-angled. Unless you're directly behind me (and my eclipse-causing arse), you're probably gonna see it.
Note that I am not telling you, dear reader, to ride around with outdated lights. With the size of my audience, even losing one would be somewhere between a 33% to 50% reduction. I'm just telling you to choose the light that works for your riding situation. Also, once you think you have the right setup, fire it up and walk away from your bike. How does it look from the front? The side? Don't assume you're visible because the road lights up in front of you while riding. See how it looks from the other guy's perspective.
(Ulterior motive... I'm hoping that good pal, frequent commenter, and professional electron wrangler Steve from Peoria will chime in with the World's Perfect Bike Light. Of course, it will be something he made in his top secret laboratory that isn't available to mere mortals. But, Steve, if you want to write a guest post on one of your retina-searing creations, mi blog casa es su blog casa.)