Originally Posted by
mattcalifornia
A tightly focused beam seems like a major drawback for a rear light. I want to be seen from as wide an angle as possible. Many accidents occur at intersections or cars coming out of driveways. Let them see that flashing red light from the side.
I think that everyone should look at their riding situations and try to optimize their choice of lights.
In an urban environment, where you are worried about threats from all directions, and ones that are typically fairly close, then a light that radiates in all directions is a good choice.
My typical riding is on country roads, where the threat is very likely to be directly behind me, so I usually use a tightly focused taillight. My dynamo headlight does throw light into my spokes, as well just shining to the sides somewhat, so this also provides visibility to the sides (this ends up being important when stopped at the few intersections along the way).
I did take some photos in 2016 to compare two different tail lights.
One was my favorite little battery powered Cateye Rapid 3 with a tight beam, and the other was a new Nashbar Radflash light that was given to me that radiates in all directions.
a shot of the two, side by side...
The Cateye was mounted on the seatstay, and the Nashbar Radflash was strapped under the saddlebag...
Near sunset, I took the bike out, leaned it against a tree, and took some photos from about 50 feet away. This is pretty close... you'd want a car to see you long before they got within 50 feet of you, but I wasn't set up to get good shots from a more realistic distance.
Two shots of the Cateye in steady mode... one that is directly behind the bike, and one that is off-axis (displace to the left a bit). You can see that the brightness drops off quite a bit when off-axis.
These are shots of the Nashbar Radflash, which radiates in all directions. You'll note that it's just as bright on-axis as it is off-axis (as far as I can tell).
and now to directly compare the two lights, both on-axis and off-axis.
This does indicate that the Cateye appears much brighter than the Nashbar light even at this close distance when on-axis, and dimmer when off-axis. These differences will be much greater at greater distances.
My point isn't that one is better than the other, but that they are different, and this should be considered when making a purchase.
A secondary point is that you really need to view a light from a large distance to get some idea of how visible it is. Don't just hold it in your hand and say "that's bright!" when you are in the store.
Steve in Peoria
(remind me to tell you about the driver that knocked my pannier off my bike while I was riding home at night. He came back to check on me, and commented on how he could see me tail light... but still somehow hit me! The point... even if they see you, they might still drive towards you. I've had people do this in the daytime too)