Cycling at Night
NCBC Meeting Handout - March 5, 2001
By Bruce Rosar and Steve Goodridge
For good reason, North Carolina state law requires bicycles operated at night to be equipped with a headlamp in front and a red light or red reflector in back. Never ride at night without a headlamp and a bright rear reflector. Although most bicycles are sold with small "toy" reflectors, these are terribly inadequate for safe night cycling. The car-bike collision rate is several times higher at night than during daylight, but the vast majority of these crashes involve cyclists operating without proper nighttime equipment and can be easily prevented. Proper equipment makes cyclists visible to motorists and can make cycling at night much safer than statistics suggest that it is.
Being Visible and Predictable
Proper bicycle lighting is important for two reasons:
1. It makes you visible and predictable to other road users
2. It can help you see well enough to avoid hazards and navigate your way
Many cyclists ride in urban environments where they feel that they can see well enough to navigate, so they dont bother with headlamps. This is terribly dangerous, because without a headlamp, motorists often do not see them, even under street lamps. Reflectors provide good visibility for overtaking traffic, but most dangers of car-bike collisions come from the front or side of the cyclist. The headlamp beams of motor vehicles on intersecting paths with cyclists often do not shine upon the reflectors of a bicycle until it is too late for the motorist to yield right of way or avoid collision. Figure 1 below shows the positions of two vehicles that might be about to move across the cyclists path. In neither case are the vehicle headlamp beams shining on the cyclists reflectors. Only the active emission of light from a headlamp can make the cyclist sufficiently visible in these situations.
Figure 1: Car headlamps often do not illuminate the cyclist's reflectors, creating a danger at intersections. A headlamp on the bicycle is much more visible to motorists in these locations.
Bicycle headlamps should emit a steady white (or nearly white) light because this indicates the direction that the vehicle is traveling. Most vehicles, including aircraft and boats, exploit a color convention to indicate orientation or direction of travel. For road vehicles, red lights belong in back, orange lights on the side, and white lights in front. The fact that reverse-gear lights of a motor vehicle are white provides an important cue as to what the motorist is about to do. Its important for cyclists to comply with this convention in order for other road users to predict their actions. For instance, using a red lamp on the front of a bicycle is likely to cause opposite-direction divers to underestimate the closing speed between vehicles because they will expect the red-lighted object to be either stationary or moving in the same direction.
A red rear lamp or reflector makes a bicycle visible to overtaking traffic. Its important to make this reflector or lamp large enough and bright enough to be seen by motorists at enough distance to slow or stop in time when traveling at high speeds. Color is generally less important on the rear of the vehicle, since overtaking motorists will not be any less cautious when viewing another color, but red is a universally understood warning indicator. A variety of red LED (Light Emitting Diode) tail lamps available for bicycles; these lamps are visible at longer distances and a wider angles than most reflectors, and dont depend on motorists headlights to be effective.
Note that side reflectors dont hurt, but they are rarely of much use because if a cars headlamps are shining on them, you will either be riding ahead and out of the way before the car arrives or it is already too late for the motorist to avoid you.
Seeing Whats Ahead
The amount of light your headlamp needs to shine on the roadway in order to see your way depends on where and how fast you ride. A cyclist riding at high speed on a dark rural road needs a long, relatively narrow beam of light to see surface conditions and obstacles far enough ahead. A mountain biker riding over challenging off-road terrain needs a wide, bright beam to find suitable paths over obstacles and around turns. By contrast, an urban cyclist operating under street lamps requires just enough beam strength to allow navigation of the occasional dark stretch at reduced speed.
The faster you ride, the longer your effective headlamp beam needs to be; if you double your speed, you need to see twice as far. Note that since the power of reflected light decreases in proportion to the square of distance from the lamp, doubling the range for a given reflection power requires four times as much light power from the lamp. For a typical headlamp beam pattern, a motorist traveling at 60 mph needs a headlamp of about 10,000 candlepower to see well; a cyclist operating at 15 mph can see well enough with less than 600 candlepower (e.g. 12 watt halogen), and a cyclist operating at 7.5 mph can see far enough in with less than 150 candlepower (e.g. 3 watt halogen). The light provided by a bicycle headlamp may be focused into a narrow beam for maximum range, or may be spread out for better peripheral vision. A three watt lamp can be focused into a beam suitable for high speed cycling on the darkest roads, but will not give much illumination of turns. Any headlamp, even the cheapest clip-on battery kind, is much safer than none at all - you just need to ride slower to compensate for reduced range.
On totally dark roads, our eyes adapt to the darkness and allow us to see surprisingly well with a low-power headlamp. However, street lamps and the headlamps of oncoming cars can inhibit or reverse the adaptation of our eyes. This makes cycling on partially-lit roads or with oncoming traffic on rural roads more challenging with low-power headlamps. It's a good idea to use the most powerful headlamp available for your cycling needs and your price range.
Special Hazards to See
Remember that motor vehicle traffic isnt the only hazard at night. Dont be surprised to find animals, unlit pedestrians dressed in black, and unlit wrong-way cyclists in your path at night. Look for them carefully, and give them wide berth when you see them. Also remember that its harder to see potholes and gravel. Also, wet road surfaces do not reflect as much light as dry roads, making driving lights (head and frame mounted white lights) less effective.
Increased Hazards from Motorists
On average, the percentage of highway users who are impaired by fatigue, poor night vision and alcohol increases at night. Drunk, drowsy, and severely distracted drivers are the greatest threat to lawfully operating cyclists at any time of day. Fortunately, the total number of motorists on the roads usually decreases at night. Many experienced night cyclists who use proper lighting report that overtaking motorists give them wider berth after dark. With reduced traffic and strong lights, it is arguable that the properly equipped night cyclist may actually be more visible and easier for motorists to avoid than the daytime cyclist.
Avoid Riding into the Sun
One situation which cannot be helped by night equipment is poor cyclist visibility when riding directly into sunrise or sunset. Motorists are often blinded to the point that they can barely see more than the outlines of motor vehicles ahead of them, yet they continue to drive at normal speeds. If possible, simply wait for the sun to set (you have your lights, right?) or to rise higher before riding; otherwise try to stay farther right out of the normal traffic stream and keep in mind that motorists approaching from behind may not see you.
Choosing the Right Equipment
A variety of bicycle headlamps are available depending on the users preference for range, light output, mounting style, and cost. Helmet mounted lights put the light where you're looking. Bike mounted lights put the light near where you bike is going to be very soon. For maximum effectiveness, use both. Note that its also good to have a back-up light source or spare bulbs and batteries(and the tools to change them).
The cheapest, shortest-range lights suitable for emergencies or occasional urban use are low-wattage clip-on lamps powered by batteries stored inside the lamp housing. These lamps can get you home safely when youre out after dark, and are good as a back-up, but they dont have enough light output for high speed cycling on dark roads, they have limited range, and they eat batteries.
Rechargeable battery-powered lighting systems provide the highest light output, making them especially popular for mountain biking, and can offer operating times of over two hours between charges. Some even have fuel gauges and multiple power settings so you can control your range. The high power availability allows wide beam width which also maximizes visibility to motorists. Recent advances in battery and lamp technology provide increased power efficiency, lower battery weight, and easier charging, than previous battery-powered headlamp systems. However, these lamp systems usually cost over $100. Examples of battery light manufacturers include NiteRider and CatEye.
For unlimited range without the worry of battery maintenance, generators are the ideal choice. Generators may be built into the front hub or attach to the tire. Early-generation generators would not provide any light with the bicycle stopped, would glow dimly at low speed, and could potentially burn out the lamp at high speed. Many modern generator systems use smart electronics to regulate power production such that the lamp is bright even at slow cycling speeds, and ensure there is no danger of burnout at high speeds. Some are even combined with rechargeable batteries to provide illumination when stopped; the batteries recharge while the cyclist is moving. Generator powered lights reduce your acceleration ability somewhat because of the extra drag, which may be 10% of your pedaling effort. Some generators, such as the Schmidt Dyno Hub, are built into the front wheel hub. Bottle generators, such as the Dynosys LightSpin, rub against the tire.
Front strobes or flashers may also add to the cyclists conspicuity. However, these should not be used as a substitute for a normal headlamp.
When conditions are right, reflectors can be as visible as rear lamps - but conditions are not always right. Bicycle and automotive reflectors use the cube-corner reflection principle to reflect light back along the same path from which it came. This means that the observers eye must be very close to the light source - less than a two degree arc, in fact - to see a strong reflection. If the drivers side headlamp is not turned on or working, the reflector may not be visible to the driver. The reflector must also be close to perpendicular to the observation angle.
Most bicycles come with small reflectors required by the Consumer Products Safety Commission. These reflectors are too small to provide adequate visibility under many realistic road conditions. A typical CPSC reflector provides only 1.7 square inches of directly exposed surface area and 1 square inch of surface angled to one side under optimum viewing conditions. The cyclist is better off replacing this rear reflector with a larger one from an automotive store. A 3" diameter round automotive reflector provides 7 square inches of reflector area. An oblong "trailer" reflector provides six square inches.
Note that an amber reflector is 2.5 times as bright as a red reflector under the same headlight illumination. By law, a red reflector is required, but adding an amber reflector to the red one isnt a bad idea. With this combination, youll be over ten times brighter than with just one CPSC reflector.
Reflectors are very sensitive to mounting location and orientation. Reflectors on the frame should be mount low to reflect the lights of other vehicles sooner. The face of the reflector should be perpendicular to the ground. If the rear reflector is where it may be sprayed by mud from the tire, clean it often.
Inexpensive tail lamps, typically employing red, energy-efficient light emitting diodes (LEDs), dont rely on a motorists headlamps to be visible, and can be seen clearly from the side as well. These lamps will last many hours on a pair of disposible batteries. However, they often glow dimly long before they fail; its important to inspect them before each ride and change the batteries regularly, especially in cold weather. Above all, use a reflector in addition to the tail lamp so you have a backup.
Some extra-bright tail lamps, such as the NiteRider Tail Lamp, run off of the same rechargeable battery used for the headlamp. These are excellent for long-range visibility and are even visible in daylight.
Solid versus Pulsating versus Flash
There is some controversy over whether pulsing tail lamps are better than solid tail lamps. A rapid pulse is better than a slow flash, because it is easier to track visually. (Remember the difficulty catching fireflies between flashes?) The rapid pulse is also grabs attention more readily at long distances than does a solid lamp. Proponents of solid lamps say solid lamps are just as visible at short distances, which they say is what counts, that solid lamps are less annoying or distracting, and that there is little use in looking different from other traffic. Proponents of flashing lamps believe that is useful to alert motorists to the presence of a bicyclist farther ahead so the motorist can better prepare in advance to overtake with caution.
General Conspicuity Tips
con·spi·cu·i·ty : The quality of being conspicuous; obviousness.
con·spi·cu·i·ty equipment : Equipment to make an object more noticeable.
Conduct a survey of your conspicuity in the dark. If you can, have a friend ride with your clothing and equipment while you check out the conspicuity under different lighting conditions.
To increase your conspicuity, display bright colors that contrast with your surroundings. Fluorescent lime-green and lime-yellow are the best. Red and orange are not as bright, and white can be problematic in visible moisture (fog, snow, etc.).
Use retro-reflective materials on clothing and equipment. Consider adding retro-reflective carriers, such as a vest and bands (wrists and ankles). Stick-on retro-reflective material can be applied to spokes, helmets, fenders, pedals, racks, shoes, panniers, etc. Redundancy and diversity are both good attributes for conspicuity equipment.
The effectiviness of conspicuity devices suffers when dirty or worn. Inspect and then clean, repair or replace conspicuity equipment as required.