Bike lighting systems - a primer

[with thanks to Doug May for much of this material]

Bulb types
There are 4 different bulb types (LED, standard, halogen and HID) and more options in battery types (alkaline, sealed lead acid, nickel cadmium or Nicad, nickel metal hydride or NiMH, lithium ion, etc).

Halogen bulbs have been used for some time and you can them dirt cheap from anywhere. A 10W bulb will do on a trail you just have to use one with a narrow focused beam. The light from them is ok however it looks yellow when you compare it to the spectrum of a HID style light. The poorer the quality of light the more strain it is on your eyes and in a long AR you'll drift off and be talking with Elvis that much sooner.

HID lights are around 3x as bright as a halogen for the same energy usage i.e. a 10W HID measures at 3x the lumens of a 10W halogen or the equivalent of a 30W halogen. This means that from the same energy source you roughly get 3x the run time for the same amount of light. More than that, the light spectrum is closer to daylight giving a better depth of field and therefore a perception that the light is brighter again.

Normal LEDs are not adequate for mountain biking and standard bulbs take a lot of power for a low quality light. But recently super-bright LEDs have been developed that provide several advantages for mountain bikers. First, they have a lower power consumption, generally using a 3.6 volt battery pack, with a much longer burn time for a given battery capacity. One of the best currentl y available, and almost certainly the best value for money, is the MinMin lights being made by Peter Blakely in Cairns. Send an email to [email protected] for more information.

Batteries

Alkaline batteries hold up to three times the energy of a basic rechargeable but are not reusable.
Home-made lights often use sealed lead acid (SLA) batteries because they are cheap, easy to charge, and are available in various sizes. The disadvantage is that they are considerably heavier for the same capacity, and the light becomes dimmer and more yellow as the battery discharges.

NiMH batteries are not much more expensive than NiCad and they have a greater capacity with a more even output level over their discharge time.

The next step up is NiMH which has a major weight saving over SLA hence a better weight/capacity ratio.
The latest generally available battery technology is Lithium Ion (L-ion). This takes the weight/capacity ratio significantly higher and has steady output characteristics. L-ion will not develop a memory diminishing it's capacity and can be charged in any part of its cycle. The trade off with NiMH and Li-OH is the need for particular chargers and the cost.

You can find a good description of battery theory here.

Calculating power consumption

To work out your power consumption divide the power rating (wattage) by the battery voltage. This will give the amperage required to run that particular light. For example,

A 10W bulb run on a 12 battery will draw 0.83 amperes.

Now the tricky bit - Not all batteries are created equal. The amount of charge a battery holds is measured in ampere-hours (A/h). C size rechargeable cells are commonly used in power packs and range from about 2.2 to 4.7 A/h depending on how much you want to pay. That means you can get more than double the use out of a quality battery. To determine the run time of your lights divide the A/h rating by the required amps:
4.7/0.83 = 5.7 hours burn time. (double that for a 5W bulb)

Using NiMH cells the voltage of each cell is 1.2 volts. So for a 12V system you need 10 cells. These weigh 86g and cost approx $15 each for the expensive 4.7 A/h version. This gives you a battery pack that weighs about 900g built weight and costs $150.00.

It doesn't sound all that cheap until you work out that a quality halogen bulb, clamps to hold it on the bars, some wire and a switch cost less than $30.00. Note the discussion on bulb quality at the web sites below.
You need to charge the batteries of course and again the amount you want to spend determines how fast you can charge them. The best charger you could reasonably ask for can charge the above pack in an hour and then automatically switch to trickle charge. I use a Master Instruments MW8165 – it runs of 12V DC (so can be run from a car cigarette lighter or direct from a car battery) and costs about $80.00.

Other factors to consider:

• Beam spread – narrower is good as a spotter, also for focussing on single track (in conjunction with a wider beam).
• Location mount – bar mounted is fine for fire trails, and I find that a dual powered (5W/10W), wider beam light is a good option. However, you also need a helmet mounted light to search for trails either side, and spotting checkpoints.
• Battery mount – there a various commercial brackets for mounting on the bike frame. It is also fairly simple to build your own to suit.

Other resources for home-made lighting systems:

• Nightlightning - A NZ company that manufactures lights and supplies components and a DIY kit
  
• Fat Hippy - A pretty good source of DIY wisdom for bike lights
  
• Light & Motion - A US company, their site is a good source of info on the type of systems available
  
• Hired Goons - Another good Australian source of DIY wisdom