Which one would be good for riding in daytime especially when it's sunny?

  • 2
    Especially in daylight, a lot depends on the lens and how it focuses the light. Jul 10, 2022 at 0:31
  • 2
    are we talking real lumens or chinese lumens? 450lm seems improbable for a rear light
    – Andy P
    Jul 10, 2022 at 8:19
  • 1
    Real lumen as I'm getting the Cateye Viz. Which Cateye Vis is good, 150, 300 or 450 then?
    – Sam
    Jul 10, 2022 at 9:07
  • I use a pair of "Lezyne LED Femto USB Drive Light Pair". They're bright enough to be seen, but not too bright that they blind drivers/pedestrians/other riders, and don't need a massive battery. The front is 15 lumens, and the rear is 5 lumens. road.cc/content/review/268425-lezyne-femto-usb-drive-pair 150 lumens is overkill, as is anything above that. Jul 11, 2022 at 9:38
  • 1
    Blinding all drivers because you don't like speeders is not only petty, it reduces your safety on the road, both because their vision is impaired, and because they'll be annoyed. Picking fights with operators of 4,000 pound vehicles is always a losing proposition.
    – user36575
    Jul 15, 2022 at 14:03

6 Answers 6


Which lights are you considering? Even 150 lumens seems astoundingly powerful. For comparison, the Bontrager Flare R City (which I use) is already somewhat irritating to look at after a while, and it's only 35 lumens. I'd hate to be driving behind someone with a 450 lumen rear light blinding me. Having a bright and noticeable light is not helpful if you blind or annoy drivers behind you.

The primary factors in my mind for a rear light would be battery life, the optics / beam shape, and the flash pattern. Obviously, a long battery life is practical and convenient. A good beam shape ensures you are seen from a variety of angles (not just from straight backwards). An interesting flash pattern which mixes a variety of pulse durations can help attract interest without expending too much battery energy. Note that flashing lights are not legal in every jurisdiction.

  • The Cateye Viz light.
    – Sam
    Jul 10, 2022 at 9:02
  • 4
    @Sam To quote the first review I read online: “My initial impression of this light was that it is too bright - LED lights can be very jarring to some and I want to be considerate to others.” “This light is bright enough for all urban environments and whilst it has a couple of flashing modes that conserve battery life, I'd advise against using them because they are unnecessary, aggressive, and can trigger seizures in onlookers.” Not a good choice in my opinion. You really don’t need that much brightness.
    – MaplePanda
    Jul 10, 2022 at 16:32

The measured brightness is less important than the beam formation, or lens configuration.

Ideally for daytime usage, you want a rear light that gets driver's attention and lasts the whole ride. It also has to not overheat in sunlight.

Whether that light can blink, strobe, throb, pulse, or has to stay on solid depends on your locality and the road regulations. Most of the world would accept a blinking red rear light in the daytime, but do check.

For daytime use I personally choose a light that has a sharp on-off profile, and a beam shape that covers the rear-most 90 degree arc.

By contrast at nighttime I prefer both a solid-on red and a throbber that moves from low to high and back again over ~1 second rather than the sharp-edged and blinding. So your DRL might be a different unit to the nighttime one, or the same light running in a different mode.

Consider that a rear light is not a "seeing" light, its a "be-seen" light, and the lower lumen levels are perfectly adequate at that. By contrast the front light needs to illuminate the land in front of you and needs more "throw"

And a lower lumen level will run for longer on a charge, meaning less chance of it going out suddenly. I always ride with multiple lights, but on some commutes I've lost almost all due to flat batteries exacerbated by cold.

Answer: lumen level is less important than other considerations.


50 lumen is a typical car brake light. Quite irritating if constantly on right in front of you.

150 and possibly blinking is WAY too much. It can blind and disorient a car driver or a bicycle rider with whatever bad consequences you can imagine.

300 and 450 are proportionally worse. 450 is a typical (maybe somewhat worn out) car headlight.

The good news is that you probably can't easily find a honest 150 lumen rear light.

Please, pretty please, constrain yourself to 20 or 30 lumen for your rear light.

  • 3
    You are underestimating car light brightnesses. 50 lumens isn't a brake light, not even a car rear light. A car rear light is 5 watts and brake light 21 watts, so a rear light is slightly below 100 lumens and brake light slightly below 400 lumens. A car headlight (halogen) is 900 lumens dipped beam, 1500 lumens high beam.
    – juhist
    Jul 10, 2022 at 10:27
  • 3
    @juhist you are underestimating the car light optics. A 21W bulb used for the brake light has ~150 lumen (when new, 7-8 lumen per watt is pretty good yield for an incandescent non-halogen bulb), after half of it hits the the reflector it is like 120 lumen and after the red filter that absorbs 2/3 of the visible spectrum in order to make the white light red it is maybe less than 50. The rear light is likely 10 lumen, considering that the 5W bulb is less efficient. ...
    – fraxinus
    Jul 10, 2022 at 10:48
  • 2
    ... In headlights, I think 1500 is the absolute ECE maximum, the usual case is ~15 lumen per watt for the bulb (it is 60W for high beam) and about 20% loss in optics that gets you ~650 lumen for each high beam when everything is brand new. One gets about 1000 lumen with xenon or LED, again with everything brand new, but both xenon and LED dim as they age as well.
    – fraxinus
    Jul 10, 2022 at 10:55

When designing a rear light for my bike I did various tests. The most difficult one was on a small country road in a forest. The bike was in the shadow from the trees, and we picked the time of day when the sun would hit the friend driving the car behind me right in the face and blind him.

Without a rear light, the bike was pretty much invisible to the driver, because it was in the shadows. And I was riding in a bright orange t-shirt.

I settled on a bunch of high-candela red LEDs, some of them aimed towards the sides for intersections, and some aimed towards the back. It is important to focus the beam of light in a tight angle horizontally, but in a wide angle left to right, so it is clearly visible to a driver far behind you or to the sides, but will not blind the cyclist riding right behind you by sending too much light upwards into his eyes.

Blinking frequency around 5 Hz. It was very safe and visible in the above worst-case scenario.

This consumes about 0.3W when on (less when blinking) so it should be at most 10 lumens, considering the lumen efficacy of red LEDs is low because the lumen unit includes the eye sensitivity, which is low in the reds.

Obviously it has a light sensor, so at night it stops blinking and switches to a more civilized intensity.

Now a more technical analysis of the thing.

First, the cyclist is riding with a symmetrical beam front light instead of a proper StVZO which means he cares neither about blinding other people, nor about seeing the road.

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Second, visibility towards the side is... mehhh... terrible. I made sure my light beamed out more than 180° around the rear, so if I'm arriving at an intersection, the driver arriving perpendicular can both see the front and rear light so they know it's a bicycle. That cost two extra 5 cents LEDs. But they didn't think about that.

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Third, it costs 40€ and they couldn't include a 2 cent light sensor to make it behave properly at night? Come on.

Fourth, it has a rechargeable battery. So if the battery's out, you can't put in a fresh AA, you have to wait for it to recharge.

Fifth, it can be mounted vertical or horizontal, which means it has a symmetrical beam and will blind cyclists behind you.

Basically, 450lm rear light is simply retarded. It won't just make drivers angry, it will also cause any cyclist behind you to strongly want to catch up and make you eat the damn thing.

A 3€ blinkie on the back of the helmet is a much better option. If you come out from behind a row of parked car at an intersection, drivers coming perpendicular can see it.


You need to consider your use case:

  • Are you looking for a light for use at night? In that case they're all far too bright. Anyone coming up behind won't be able to see anything except the red dazzle.
  • Are you looking to be spotted in daylight by a driver approaching at speed, as early as possible (even with bright clothing, if you're in and out of shadows you may want lights)? In that case all of them still seem too bright, with the possible exception of the 150 if it spreads the light over a wide arc. The 450 certainly does illuminate on a very wide angle.

Even reputable manufacturers sell unreasonably dazzling lights - this is particularly obvious for front lights which do have uses e.g. on singletrack, but is true for the rear as well. Some are also at that maximum brightness for a very brief flash. For the rear lights, some seem to be sold on the assumption that you'll mainly use the much lower power options. Note though that Cateye's description is a bit odd:

Constant (40 lumens):5 hrs
Flashing (40 lumens):65 hrs
Group Ride (130 lumens):10 hrs
Daytime Hyperflash (450 lumens):14 hrs

That "group ride" mode is only suitable for a back-marker, unless you want the following rider to hit you or a pothole, because they won't be able to see a thing.

Note that red lumens are not the same as white lumens because the definition of the lumen takes into account the sensitivity of the human eye, as well as rear lights not needing to illuminate the ground. So you should expect much smaller numbers than you would for front lights.

As a point of comparison: The Lezyne Zecto Drive has an 80 lumen "daylight flash" mode. Mine is an old version so may be a little less, but it's very visible even in sunlight, quite annoying close behind at dusk (but that's when I use it most, if I don't expect another rider behind - on Saturday, for example, I was heading into the sunset solo), and dangerously dazzling in the dark. The main night time modes on the current model are 10--25 lumens; I'd expect the latter to be good for being spotted at a distance, and too much for a rider on your wheel. My main (steady) rear light is dynamo-powered and is good in the dark, less so at dawn/dusk. I often also use a light built in to my helmet for long-distance visibility.


None of these, except maybe 150 lumens would be barely acceptable.

In comparison, a car taillight bulb is 5 watts if implemented using the old incandescent technology. That's perhaps around 90 lumens. This highlights the insane brightness of these lights.

With current state-of-art LED technology (150 lm/W), those would correspond to about 1, 2 and 3 watts. Maybe a bit more as white LEDs have been optimized but red LEDs perhaps not so much.

How would you power those?

If you power those using a dynamo hub, it will take a large share of its current capacity. This will leave less current available for the front light, where you need it the most.

If you power those using for example two AA batteries (4.8 watt-hours combined), you get runtimes of 4.8 hours, 2.4 hours or 1.6 hours (perhaps little less because a switch-mode converter doesn't have 100% efficiency). That seems bit too little for my tastes, although 4.8 hours might be barely acceptable if you use rechargeable AA batteries instead of disposable ones.

Usually you select a rear light that consumes little power, and use most of the power for the front light.

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