Daytime Tail Lights: A Couple Things….

First and foremost, I’m convinced that running a GOOD tail light during daylight hours is a great idea.  Yeah, yeah… yet another dorky thing to the fashion conscious cyclists.  Get over it: to most of the non-cycling world (that would be about 95% of the people in cars who actually see you cycling), if you ride a bike on the road you ain’t cool anyway, no matter how fast and fit you are or how blinged-out your bike is.

Now that that’s settled, let me point out that just having a tail light on your bike doesn’t mean it will provide you with the visibility you intend.  There’s a bit more to it than that, in much the same way as getting the expected protection value from wearing a helmet.  Let’s face it, we’ve all seen people wearing helmets that aren’t fitted correctly, with loose straps, or that should have been replaced years ago: net result is that they may or may not protect someone’s head if they should have a fall or collision.  I call these placebo helmets…

Tail lights are no different.  If the light doesn’t actually make you stand out and get the attention of motorists far enough in advance, then it’s just decoration.  To be effective in daylight hours, you need a GOOD tail light, it also has to be positioned and aimed correctly and have ample juice in its batteries.

Here’s the deal, ever since seeing our first DiNotte 140R taillight on the back of Bob & Jan Thompson’s tandem during the 2008 Southern Tandem Rally in Bowling Green, Kentucky, I’ve always taken note of how well (or not so well) other tail lights do at making a bike stand out in day time riding conditions.  Honestly, there are only about 1 out of 20 tail lightsI see that are getting the job done.   Some of the lights are good products like the Planet Bike SuperFlash, the Cateye TL-LD1100 and TL-LD600.  Of course, the DiNotte tail lights always standout light a beacon on a hill a mile away… really, they do.

While this isn’t the best quality video, it does give you a sense the directional nature of LED tail lights and how quickly the intensity falls-off as the direct line-of-sight into the LEDs shifts up, down, right or in this example left.  Note that the video image distorts the brightest light into an almost light-red to white light which is what you’re seeing when the video starts with the five different tail lights lined up and flashing.

So, the point is, even some of the better models of tail lights become less than effective if they’re not positioned and aimed correctly.  This is because LED-based lights are very much directional, which is to say the LEDs are only at their brightest when they are looked at straight-on.  Therefore, if an LED tail light is pointed a little up or down instead of straight back it looses a significant amount of its intensity and range.  This is one of the reasons I really don’t favor lights that are attached to the back of helmets, clothing or saddle bags and the like as they tend to be pointed in all the wrong directions, instead of back towards on-coming traffic and motorists.  Therefore, if you’re installing a tail light on your bicycle, make sure you take the time to select a light that can be mounted where it can be positioned to point straight back with the LED light path parallel to the ground (excluding DiNotte and other super-bright lights that should be pointed slightly down).  And before deciding that you’ve got it positioned correctly, prop your bike up with the light on and move back 100′ to see if you need to fine tune the aim for maximum intensity and range.  Again, if the light doesn’t make you stand out to motorists well before they are on top of you, they aren’t of much value.

The other thing that seems to kill the effectiveness of tail lights for day time use is weak batteries.  Again, if you have a Planet Bike SuperFlash, but the batteries are only able to generate 1/2 of the light’s intended output, the light becomes of little value in grabbing the attention of motorists.  This is why having a light that is powered by a rechargeable power source or simply rechargeable AA batteries that are easy to change is something else to think about when buying a tail light.  After all, if the batteries are expensive or hard to replace, chances are you’ll either not use the light all that much or if you do, you’ll run it with low batteries from time to time, and in either scenario you’re not getting the value that the light was intended to provide in terms of increased visibility and safety.

We change batteries a lot. Like every time we ride by rotating 3-sets of rechargeable AA batteries. This allows us to always start our rides with fresh or nearly fresh batteries.  In fact, the constant changing of batteries caused a fatigue crack in the 4 – AA battery carrier for our DiNotte 140L tail light.  Fortunately, DiNotte used a very common 4-battery carrier that you can find at Radio Shack stores for about $2.20/each.  We’ve been using the same 12 AA rechargeable batteries for nearly 2-years now; very efficient, cost effective and a little easier on the environment.


Anyway, just some food for thought.  These days, given the problems of distracted motorists, it’s in your interest to do your best to be seen well down the road.  A good tail light with good batteries that’s carefully positioned is a relatively simple way to stand out.


About TG

I've been around a bit and done a few things, have a couple kids and a few grandkids. I tend to be curmudgeonly, matter-of-fact and not predisposed to self-serving chit-chat. Thankfully, my wife's as nice as can be otherwise we'd have no friends. My interests are somewhat eclectic, but whose aren't?
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11 Responses to Daytime Tail Lights: A Couple Things….

  1. Pingback: Daytime Tail Lights: A Couple Things…. « The TandemGeek's Blog » LED Taillights - Everything about LED Taillights

  2. Allen says:


  3. Wayne says:

    I agree with daytime running of rear light. I also have a DiNotte headlight and often use it during the day.

    Our route includes some narrow curving park roads where autos often take the middle of the road. I find the head light greatly reduces the instances of meeting a car around a corner in the middle of the road. Drivers notice a vehicle ahead through the trees and stay on their side of the road.

  4. Wayne Thais says:

    Take a look at this helmet light, we have one and it is really bright.

  5. Dave says:

    I have thought about getting a DiNotte taillight. The thing that has always stopped me is the web site lists the run time on high as 2 hr. Have you found a way to get longer run time?

    • TG says:

      Yes… We never run it on 100% / full-on power.

      You’ll note that run-time can be extended up to 12 hours with the 4-AA rechargeable battery model by using a slow pulse or, 6 hours using the Strobe… which is the setting we tend to use. It is VERY effective in Daylight using the Strobe, and the low setting is more than adequate for non-urban lighting conditions at night. The only time I’d use 100% steady would be in a semi- or well-lighted urban area at night or some other place where I simply wanted to light-up the night with my red tail light.

      Again, even the little 140 Lumen model is brighter than most other “good” tail lights even when it’s on it’s lowest setting.

      We also have one of the 4-cell Lithium Ion 140L models. Debbie uses on her single bike it in the Strobe mode for a week of 25 mile daily rides between re-charges. It will run for days in the most energy conserving modes.

  6. Steve says:

    I definitely agree with running a good taillight in the daytime. We have a Dinotte 140R on our tandem also. I also run a Dinotte 140A daytime running light on the front (I actually feel that there is more danger in front of me than behind me.) I run the Li-On batteries because they’re just more convenient than the AA’s and they have 2-4 times the run time of the AA’s.

  7. Wayne says:

    The low power beam of course lasts much longer. Keep in mind that low power is relative. After purchasing it I tested the taillight next to my Jetta’s rear lights in a side by side test from distance from 50 ft. to about 300 ft.

    The Dinotte low power setting is about as visible as the Jetta’s tail light. The high power appeared slightly more visible than the brake and tail light on the car.

    After that test I went in the house and ordered one for every bike. During the day we use a low setting alternating with a high setting. Has lasted on rides in excess of four hours on rechargeable AA batteries.


  8. Pingback: Distracted Driving… PSA’s & Self-Defense Techniques « The TandemGeek's Blog

  9. Paul says:

    Would you recommend that everyone in a bunch ride (say20-50 cyclists) a have a solid rear light on during the day? If so, would the drafting cyclists get “sun spots” in their vision?

    • TG says:

      A good question, but also very much like any question about economics where the answer is: “It Depends.”

      If it’s a club ride and there are 20-50 riders in the bunch then the sheer mass of the group should have very good daytime visibility, so that suggests the benefit might not be as great as it would for a lone rider. However, someone has to be on the back and if it’s not a no-drop ride then the benefit of a daytime rear tail light increases dramatically. Other factors would include where they are riding (city, urban, rural or a mix), what time of day it is (dawn/dusk vs. mid-day), how much and what kind of traffic they share the road with and the like. So, all that said, I would in such a situation have the light on my bike but may or may not have it switched on all the time.

      Now, as for the ‘sun spot’ issues, if someone is using one of the very bright tail lights and blinding a rider on their rear wheel then the light is not aimed correctly. The very bright lights are supposed to be pointed slightly down so that at night they create a large red field of light on the road just behind the rider to increase their visibile footprint to motorists coming from behind in addition to the normal tail light function of marking the location of the bike and rider. Therefore, if each rider who has a light has it aimed correctly then it shouldn’t be an issue for trailing riders. If it is and the rider with the light isn’t at risk of being dropped off the back of the pack they can always turn the light off while they are in the bunch.

      Bottom Line: The decision to use a tail light or head lights during daylight hours to reduce the risk of being hit by a motorist is a personal one, much like wearing a helmet to reduce the risk of a head injury in a crash, using a mirror to increase your situational awareness, etc. If the conditions a rider must deal with present some level of risk that can be reduced by the use of lighting during daylight hours, it’s always an option.

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