I got the Cygolite Hotshot 50 hoping it would be bright enough for daytime use, but it's just adequate in daylight and then only within the narrow aperture of maximum brightness directly behind the typical Cygolite Hotshot narrowly collimated beam.

Overall it's no better than my $15 Planet Bike Rack Blinky 5, just different. The Planet Bike rack lights combine LEDs and reflectors, so it has decent visibility across a wide angle of view. The PB has a somewhat narrow aperture of maximum brightness but that primarily affects the viewer's elevation, not lateral position. The Cygolite has a narrow aperture of maximum brightness that's much more position sensitive.

I suppose I'll keep the Cygolite since I needed to replace the balky old lights that came with my '92 Univega. It's still an improvement over those much older LEDs. And it is very bright at night, with a good selection of flashing and steady modes to suit personal tastes and local etiquette. But I won't rely on it as a daylight visible rear light.

A bit disappointing, because in the REI store the Cygolite Hotshot 50 (the most powerful Cygolite they had in stock) appeared subjectively as bright as the Niterider Sentinel 150. But both have pretty much the same characteristics: maximum brightness confined to a very narrow aperture directly behind; rapid falloff in apparent brightness from the sides; some ability to decrease brightness and flash characteristics to suit nighttime group rides to avoid distracting other nearby cyclists.

And I've added more hi-viz yellow and green cycling clothes -- jerseys, windbreaker, etc. And I plan to add some reflective tape, stickers or iron-ons. Not fashionable but should help visibility.

I've loaned both my Shimano Storm Jacket and Pearl Izumi windbreaker to other cyclists in group rides who didn't dress warmly enough, and can say those little reflective touches really do pop at night. So adding a few more won't hurt.