, mirrors and lights. There are lights made for helmets, and users have been ingenious in adapting many others for helmet use.
Advantages and disadvantages
Helmet lights are particularly useful for off road riding because the light follows the direction you are looking. Lights mounted on the bike will still be shining straight ahead when you need to see how to set up for the next turn. On the road the light may catch a driver's eye, and you can even "flash" the light briefly in a driver's eye to get their attention. We don't recommend that. It blinds the driver, or even worse, another bicyclist coming at you on a dark trail, and they experience something similar to having a camera flash go off in your face. Careful practice is required to avoid flashing people when you don't intend to. Since an important function of a headlight is identifying your vehicle to oncoming or crossing traffic, you may think that the unusual helmet-mounted light will attract a driver's attention, but in an urban setting it may be lost in the light clutter and rejected as a streetlight or sign because it is too far above the roadway. From this perspective, a car light mounted on the bicycle provides the light that drivers are scanning for, and is a more reliable indicator that you are a vehicle. At intersections, cars coming from the left or right often depend on the light they see on the pavement ahead to decide if a vehicle is coming on the crossing street.
The importance of breakaway mounts
The first and most important rule for mounting a light on your helmet is that it must break away readily when you crash or catch an overhanging obstacle. If it does not, you risk having your neck jerked when it snags on the pavement or tree. Besides jerking your neck, that can add to the g's of the shock to your brain when you hit pavement.
There is no standard for how easily the light should detach. The CPSC standard says it should "readily" detach during normal lab impacts. But "readily" is not defined. Few helmet or light manufacturers have given enough thought to their mounts. Only one helmet manufacturer we have spoken to provided their lab test levels, Uvex, proving that they actually have an internal standard. And the light manufacturer Jet Lites has a standard requiring their mount to break away when loaded with a 5 pound weight.
Some manufacturers use hook-and-loop straps to hold their lights on. We have seen some that wrap through the vents and under that seemed unlikely to detach when they should have. But again, there is no standard for that.
The greatest advantage of a fixed handlebar light for road or urban trail use is that the beam can be designed to light up the road ahead without blinding oncoming trail or road users. Car lights do a good job of this when used on low beam, cutting off the light above a certain level. We have never seen a helmet light that did that. Evaluating the beam is difficult without actually riding with the light, so we have no advice on what to look for.
The technology of bike headlights has been evolving in the past 20 years from halogen to LED's and metal halide lights. Each gain in efficiency results in more light and higher cost. Halogen lights have been essentially stable for years, but LED lights are in a period of rapid improvement, with new levels reached in 2006 and 2007 and the pace of development quickening. The LED light you bought last year is probably not as bright as this year's crop. Metal halide lights use higher wattages but have very high efficiency, giving a blue tinged light. Their high cost should come down eventually.
Low wattage headlights can be efficiently run on a bicycle using a generator driven by the bike wheel. Most generators can only produce about 3 to 5 watts without too much drag, and the resulting light was always feeble with incandescent bulbs. A three watt LED headlight can produce a lot more lumens and may be adequate for some uses. Running a traditional 0.5 watt rear light on the same generator drops the headlight wattage to 2.5 watts. Some systems have a battery to keep the lights burning at traffic stops, a time when you don't want your lights to die. Most generator lights are mounted on the bicycle, since a helmet mount would require a wire down to the generator.
Most riders prefer battery power for headlights, since you can run much higher wattage lights and see better. Rechargeable batteries can keep the cost reasonable. For helmet lights a battery included on the helmet tends to feel heavy, particularly if it is mounted above the head's center of gravity, and adds an external projection that is not optimal for crashing. Mounting the battery low can minimize the perceived weight. It needs a breakaway mount, of course. Batteries worn elsewhere need a wire connection, an inconvenience.
Headlights on a helmet, like any other light on a bicycle or any other vehicle, should be redundant--you need to have a backup for the time when the light breaks or the battery runs down. Cars have two headlights and two taillights for a good reason. Bicycle lights are generally a lot less reliable than car lights.
Rear lights work well on a helmet in combined with lights mounted further down on the bicycle. With a helmet light, a light under the saddle and a light at the level of the wheel axle, you have a better chance of being identified as a bicycle. In that case the height of the helmet light can be a big plus.
Most riders use a blinking light on their helmet. Blinking lights are off most of the time, so they use the battery very efficiently. The newer LED lights are very bright--if you have not compared yours with the new ones recently it is worth a trip to a bike store. The small LED lights are easy to mount with hook-and-loop so that they come off readily for crashing, but hold very well for every day use. The hook-and-loop has a lifespan, but it will probably last 5 years or more. If you are concerned about degrading the helmet shell with the adhesive, you can put a layer of Scotchlite reflective tape on the shell first. 3M will not say that Scotchlite is compatible with every helmet shell, but it probably is your best bet.
The problem with most LED lights is that although very bright they are too small. A driver may have the impression that your bicycle if farther away than it is. It will be difficult to put a really large LED light on your helmet, but you can mount one of the very large 18-LED models that are about eight inches wide under your saddle or on the back of your rack.
Batteries are seldom a problem with LED's, particularly those that blink. They run for months on standard AA or AAA cells. Rechargeable batteries are great if you use the Eneloops or similar that reduce the tendency to self-discharge during periods of non-use.
This page was reformatted on: April 28, 2015.