QUESTIONS YOU OUGHT TO BE ASKING ABOUT OFF-ROAD BIKE LIGHTING
...and answers too!

pseudo-FAQ by Josh Karnes of AACMB Dec. 5 2001

Revised March 6, 2002

I raced (using the term very loosely) in a 24 hour mountain bike race in November of 2001 using borrowed lights, and had lots of problems mostly due to lighting. However, I loved the format of a 24 hour race, so I decided to go ahead and get my own lights so I could do these races in the future, hopefully without the lighting problems. I am writing this document because many of the problems I had were ones that I would have never expected and had no idea to look out for, and therefore if I'd have bought lights before the event, I would have probably gotten lights that would have caused me big troubles on the trail.

I just didn't know enough to even ask the right questions, and then of course I didn't know the answers to the questions either! Now I do, so I'm sharing them with you.

Now, this is a kind of long document, but before you drop $200+ on bike lights it's probably worthwhile to read it.

If you have questions about off-road bike lighting that are NOT answered in this document, then you can take a look at the links at the end, or email me at jkarnes@cisco.com. I'm no bicycle lighting expert, but I'm pretty good at gathering information.

1. Why do I need lights?
2. What constitutes a mountain-biking light system?
3. What kinds of bike lights are out there and how much do they cost?
4. What kinds of batteries are there and what are the differences?
5. How long does it take to charge the battery and how long does it last?
6. What's the big deal about chargers?
7. Where can I get a REAL quick charger?
8. What is the difference between different bulbs? What's the deal with the bulbs? They're expensive, different manufacturers say they are not compatible with each other, I can find similar bulbs at the hardware store, so what gives?
9. What is a "digital" light system?
10. What is an "HID" or "Arc" light system? How is it different from halogen?
11. Can't I build a set of lights myself for less? If so, how?
12. What do I really need to make the ideal mountain-biking light system
13. What's the absolute, dirt-cheapest usable off-road bike light system on the market? What are the trade-offs? What's the best value for a light system out there, regardless of cost? Any other tips on buying lights?
14. Howbout some links?

I spent several months asking myself this question. I was convinced that the set I could borrow for the 24 hour race would be fine, and whenever I needed lights I could borrow them. However, I didn't realize certain things.

Firstly, and simply, you need lights to ride at night. That's all there is to it. Now, there are some hammerhead guys who do "moonlight" rides at night without lights, but that can hardly be the norm.

So then the question, why do I need to ride at night? Well, if you plan to keep on the bike over the winter and you have to work during the day, then you're either going to only ride weekends or you're going to need lights. I thought I could get by only riding weekends, then it turned out to rain every single weekend in November.

There are some other things to think about as well. The first two or three night rides you do will reveal these things, and these things will impact the choices you make for lighting. Unfortunately, you could end up buying lights, THEN discovering this stuff, then wishing you'd bought different lights.

The thing we don't think about which is pertinent to this question is that when you ride at night with lights, your perception is very different and the information your eyes feed your brain is very different than what happens during the day. The same information you use for day riding is not available for night riding. For this reason, you will need to develop new skills for riding at night. This is not just about being able to see, but dealing with the mental and physical effects of limited sight on the trail. For this, you need practice. So, if you plan to ride at night occasionally, then IMHO don't bother, it's pretty stressful and dangerous. If you want to ride at night effectively, especially at a 24 hour race, then you need to practice riding regularly in the dark and learn to use the bike with lights on it all over again.

A mountain bike light system consists of at least one light assembly, at least one battery and at least one charger. There are generally two types: handlebar-mount (AKA "headlight") and helmet-mount.

The light assembly is a light housing (generally round thingy that holds the bulb), a bulb, and some aparatus for mounting it. For a handlebar light, the light housing is mounted to the handlebar by some mounting method; the better lights have a quick-release clamp so you can get the light on and off the bike quickly and easily. Even better ones have an offset clamp that enables you to mount it to the handlebar in a way where it's centered over the stem. Many handlebar lights have more than one light and have a switch that can be mounted easily (usually velcro) to the handlebar near the grip so you can switch from one light to the other (or to both).

Helmet-mount lights have a "base" which is velcroed to the top of the helmet by running a strap through the vent holes. Some helmet-mount lights intend for you to use adhesive velcro on the helmet and on the light base, but this is not nearly secure enough for off-road cycling. Better helmet mount lights have a solid angle adjustment apparatus.

Some lights are "convertible" from helmet to bar mount. Usually they are not ideal for both purposes, as there are very different requirements for bar and helmet lights.

The battery is a rechargeable number that can be mounted somehow either to the bike or to the rider (bar lights mount batteries to the bike, helmet lights stow them with the rider). Some batteries are designed to work for either, but they generally are not ideal for both. The better bar-mount batteries are constructed so they are shaped like a water bottle and can snap into a water bottle cage. The better helmet lights have a battery which is very compact and can be easily stored in a hydration pack or a jersey pocket. Some have a largish rectangular battery which may be strapped to the frame inside a velcro/nylon bag that looks like a small camera bag or just stuck in a hydration pack or "fanny pack". There is a lot to the battery so I'll cover it in detail in a later question.

The charger is usually a wall-wart type thing that plugs into the wall and into the battery. There is a lot to the charger so I'll cover it in a later question.

There are bike lights ranging from AA or C-cell powered handlebar-mount lights that can cost under $10 all the way up to Halide-arc "HID" lights with digital controls and high-end fast chargers for over $400. They range from just over 1 watt to over 40W total power.

By and large, most useful mountain bike lights are in the range of 10-40W total power, generally have two lights (a "high-beam" and a "low-beam"), are handlebar mount, have a battery that'll run just about 1-2 hours on the highest power setting and cost about $60-250.

OK, now we're getting somewhere :)

There are three types of batteries in common use today in bicycle light systems: Sealed Lead Acid ("SLA", "Gel-cell"), Nickel Cadmium ("NiCd", "Ni-cad") and Nickel Metal Hydride ("NiMH"). There is one new type of battery which is in use in camcorders and cell phones but not yet available for bike lights, that's "Lithium Ion".

SLA batteries are the cheapest, heaviest, slowest to charge, deliver the least current, are the worst as the weather gets cold, have a linearly-declining voltage discharge curve which makes the lights get yellow as the battery gets even slightly drained, and are generally not a very good choice for bike lights. They are, however, very common in the cheaper light systems, they are very tolerant of constant "trickle" charging, and they hold their charge for a long time without being on a charger. They are very easy to charge and are not commonly damaged by using cheap "dumb" chargers. The pros of this system are the charge simplicity and the price.

NiCd batteries are much lighter than an SLA of the same capacity (like 40%), are less than half the size of an equivalent SLA, have much lower series resistance than SLA so they can deliver more current, have a discharge curve such that the voltage stays very high until they are almost completely flat when they drop quickly, and they hold a charge reasonably well but not as well as SLA. They can undergo about 500 charge/discharge cycles which is maybe half that of a typical SLA. They are easily damaged from overcharging and require a charger which has some means of preventing overcharging, also known as a "smart" charger. They can be fast-charged. They are about twice the price of SLA, but are the cheapest of the really useful bicycle light batteries.

NiMH batteries are about half the size and weight of NiCd of the same capacity and have almost all of the pros of NiCd, only better. They have an even more flat discharge curve, with the voltage staying higher longer into the discharge cycle and then dropping only at the very end. They don't, however, hold a charge on the shelf nearly as well as NiCd. They also are much more sensitive to overcharging than NiCd and require an even more advanced "smart" charger than NiCd. They have about half the charge/discharge cycles of NiCd.

The talk of size and weight are important because you only want to have to carry one battery, and it probably will have to fit in a water bottle cage. For a 20W light, a SLA battery that fits a water bottle cage will get you to just under 1 hour of use. A NiCd will run about an hour and a half or so, and a NiMH can run over 2 hours. Of these equivalent sized batteries, the SLA will be way heavier than the NiCd, and the NiMH will feel light as a feather compared to the NiCd.

The means of mounting the battery to the bike or person is very important for a few very good reasons. If you lose the battery, like if it falls off on the trail, you will have no light with which to find it. Ever heard of "SOL"? This is a good time to mention carrying a backup light (like a little Mag Light) just for this purpose. Anyway, if the battery falls off during a ride, the cable might break, it might break the battery or damage it, it might fall off in a creek or underwater, etc. Trust me, you don't want any of these things to happen at 10:30pm when you're 5 miles from your car in pitch black woods.

Batteries that mount in the water bottle cage are probably the best for bar lights. You can supplement the tension of the bottle cage with a toe strap or some velcro or something so you are real sure the battery is not going anywhere. These "battery in a bag" things with velcroed-on nylon bags are most definitely high-risk. Velcro might be great stuff, but I don't want it to be the only thing holding my light battery on the bike, thanks. For helmet lights, compact batteries that fit securely in a compartment of your hydration pack are certainly the best. You won't lose that!

The battery will be rated in voltage and in what is called "ampacity". "Ampacity" is a term of "amp-hours" or "Ah" which is written on the side of the battery or in the ad copy of the light system. This is a rating of how many hours the battery will deliver one amp, or how many amps the battery will deliver for an hour, or any mathematical function thereof. For example, a 4Ah battery will run at 4A for an hour, or at 1A for 4 hours, or at 2A for 2 hours, or any other combination of amps and hours which, when multiplied together equals 4.

Now, this is pretty useless unless you know Ohm's Law like the back of your hand, because bike lights are not rated in "amps", they are rated in "watts". What you need is "Watt hours". To get this, you have to know the voltage of the system (usually it says that in the ad copy or specs of the light system) and multiply that by the amp-hour figure on the battery to get Watt Hours. So for our 4Ah battery from the example above, let's say that's a 6V system. You have 6x4 or 24 Watt Hours.

To know about how long the light will last on that battery, you take the Watt Hours and divide it by the number of watts the light is rated to and you end up with just Hours.

So say you have a 20W light and that 24 Watt Hour battery we discussed. Divide 24 by 20 to get 1.2 hours, that's how long the battery will last when powering that light.

Most bike light systems are either 6V or 12V, and some are 13.2V. Usually the 13.2V systems are actually advertised as 12V. The wattage is the "rated" wattage, but most lights are actually overdriven these days which is to say, the bulb is rated at a lower voltage than the voltage it's being driven with (more on that later), so a 20W bulb might actually draw more like 25W of power. When you add all this up, you get pretty approximate, but inflated numbers for discharge time.

On top of that, at some point, depending on the battery, the voltage of the battery will drop low enough that it causes the light color to change (yellow). You can't ride effectively offroad with yellow light, and I have scars to prove it. This is where that "discharge curve" above comes in. A SLA battery gets to too low a voltage way early in the discharge cycle (about halfway), so only about half of its charge is really useful. NiCd and NiMH are MUCH better. Overdriving the lights will dramatically improve this situation for all batteries.

Generally, then, probably only about 80% of the Watt Hours you calculate is really useful for NiCd and NiMH systems, and maybe only 60% or thereabouts for SLA. This really pushes the SLA way out of the running in bike lights, since not only is it heavy and bulky and all the other stuff, but it also is useful for much less of its charge time.

OK, all this math mumbo jumbo is great for some folks, but others just want a chart or table to look this up. Here ya go, for common wattage lights and batteries:

Now the other part of the question, how long does it take to charge the battery? Well, that depends on the charger. Generally fast chargers are designed to run under 6 hours and "slow" chargers or "overnight" chargers take 10+ hours.

One last note, and this is important: BATTERY MEMORY IS A MYTH!

The effect known as "battery memory" is actually damage resulting from a bad charger, or the wrong kind of charger.

Battery chargers are perhaps the most important and most expensive part of an off-road bike light system. The charger has to be properly mated to the battery type, and the better batteries require relatively advanced chargers.

The real scoop is this: As the battery gets near the end of the charge cycle, that is, it's fully charged, it will get hot and be prone to damage if it's charged past that point. It takes a certain amount of current to cause this kind of damage. If you charge it with less current than this "certain amount" (very small amount), then it does not matter how long you charge it, it will not sustain damage. However, this will take a VERY long time to charge the battery (days for NiCd and NiMH). In order to charge faster, you have to use more current, and then you risk overcharging and damaging the battery (causes what is mistakenly known as "battery memory"). In order to avoid this risk, you need a charger that can charge with lots of current so it charges fast, but can sense when the battery is fully charged and switch over to a much lower current when it gets to this point so it does not damage the battery. A charger that does this is called a "smart" charger.

SLA batteries generally are available only with cheap systems and similarly only tend to come with cheap chargers that will only "trickle" charge the battery. This means they charge with a very low current, low enough to not damage the battery. SLA are pretty immune to this kind of damage so they can usually get along with a "dumb" charger that charges the battery overnight, like in about 12 or so hours. With 6V or 12V SLA batteries, you can charge them MUCH faster with an aftermarket charger, but by then you've spent enough money to have gotten a light system with a better battery and charger anyway.

NiCd batteries do two things when they get fully charged: #1 they get hot, and #2 their voltage begins to actually DECREASE. A NiCd smart charger will sense either the temperature change in the battery or it will sense the moment when the voltage begins to decrease and then switch over to a super-slow charge mode.

NiMH batteries also get hot when they get fully charged, but by the time their voltage begins to decrease, they have already been damaged. A NiMH smart charger has to sense either the temperature change or it has to be fast enough and sensitive enough to sense the moment when the voltage of the battery LEVELS OFF.

The temperature thing sounds like a great idea but currently no bike lights use this method, they all use the voltage-sense method.

NiMH chargers work with NiCd batteries, but not vice-versa.

The result of charging the battery wrong is that the max voltage capacity of the battery (and therefore its useful discharge time) will be reduced, and eventually the battery will become useless.

FWIW, most bike light battery chargers on the market are NOT very good at charging batteries, even the "smart" ones don't do it right.

Also, it seems that MOST bike light chargers are NOT fast chargers. The main one that is a fast charger is the Nite Rider Micro Brute, but it's not THAT fast (4Ah battery in like 6 hours) and it's known to damage batteries anyway.

This is a big downer in the whole bike light scene. You're going to be stuck with a semi-inadequate charger and that's pretty much the reality. However, I have found information that may lead to good fast chargers for bike lights for those with a little ingenuity.

For those of us not satisfied with the "fast" charger options available currently, there is hope. For those of us who ride even as often as every night, an overnight charger will probably do the trick. It's charged by the time we need it again, which is tomorrow. For bicycle commuters, the Nite Rider Micro Brute will probably do the trick. Five hours is all the time you need from when you get to work until you leave for home again. However, for those of us trying to do 24 hour races on teams of 4 or less, or for those of us who are forgetful about getting the batteries on the charger far enough in advance of a ride to get them charged, then we need another option.

Fortunately, there are two very viable options.

The first is the cheapest. It's to use a DeWalt cordless drill charger modified for bike lights. The idea is to take a DeWalt charger, hack into it and put a wire on it to connect to your battery, and use it to charge the battery. What's special about the DeWalt chargers is that they are not only very fast chargers, but they are well-designed smart chargers that adapt to voltages ranging from under 6V to over 18V in some cases, and they absolutely do not overcharge the batteries. A DeWalt charger will fully charge a 4Ah battery in less than an hour. That's less than 20% of the charge cycle of the Micro Brute.

There is a catch though. The first catch is that it's incumbent on the user here to add an appropriate cable to the charger and make sure it works. This is easy to do for me, but maybe not for everyone. The other catch is that the output of the DeWalt charger is not isolated from the mains and is instead sitting at +110VAC when it's plugged in. This represents a substantial shock hazard when used with a connector. Appropriate precautions should be taken (like using a line isolation transformer between the wall and the charger) in order to maintain safety. As a professional safety engineer, I am very concerned about this particular problem, and therefore I cannot and will not instruct you as to how to modify one of these chargers to do bike lights. If you can't figure it out on your own, you have no business doing it. If you can figure it out, then you probably understand the hazards of having live circuits accessible and you're no doubt ingenious enough to figure out a way to do this safely. In any event, bear in mind you do this at your own risk.

The other catch: these chargers only are intended to work with NiCd batteries. They might work with NiMH (reports are that they do, but so far no long term data), but they are intended for NiCd. Odds are they will overcharge NiMH slightly. Odds are, imho, they won't overcharge them any more than the semi-smart "overnight" chargers typically sold with bike lights, but there is some risk.

The cost of these chargers is about $30 when you buy them used off of Ebay. The part numbers to look for are DW9106, DW9107, DW9108, DW9116, etc. Don't be afraid if they say they charge "9.6V to 18V" and you've got a 6V battery, they will all charge the smaller batteries, it is just that at the time DeWalt released these chargers, smaller DeWalt batteries were not available so they don't advertise that feature.

FWIW, if you have a 6v battery then the safety risks outweigh any benefit and you should skip straight to option 2:

Radio-controlled car (and other radio-controlled vehicle) batteries have a similar problem to bike lights only lots, lots worse. Imagine you shell out hundreds of bucks for a radio controlled car. It's fast, fun, exciting. The battery only lasts seven minutes. WHAT!?! Yep. So you charge it ALL NIGHT, then drive it for SEVEN MINUTES, that's great. Well, you're right, that sounds ridiculous. That's why the RC car guys have gotten real serious about battery charging. They have this down to where they can easily charge a RC car battery in 15 minutes or less. This is what they call "quick" charging.

How do they charge so fast? "Peak Charger". This is a charger that has a "peak" detection circuit and can detect when the battery has hit its max voltage and is starting to drop off (sound familiar?). Bingo! These can usually handle a charge current up to like 5A (so they will charge a 5Ah battery in 1 hour) and many have adjustable peak.

For Ni-Cads, almost any Peak Charger will work. For NiMH, you have to get one with "adjustable" peak, and one that allows you to adjust the peak detect to .01 or .02V max (10-20mV. This means when the voltage drops .01-.02V from the peak, it shuts off and protects the battery. This sounds nearly ideal. And it is.

What's the catch? Well, most inexpensive peak chargers only run on 12V DC. This is because many RC car guys use their car's battery to charge them at races and whatnot. Some will run on AC, but they are a generally more expensive. So you'll have to round up a suitable high-current AC/DC supply from Radio Shack and then wire it all up. The other catch? Cost. They typically cost a lot more than the DeWalt chargers on Ebay. Upwards of $100 or so is not uncommon. However, to charge your NiMH batteries safely in under an hour, when compared with the alternatives for getting a charged battery in less than an hour (Micro Brute? NOT. Multiple-batteries at a 24hr race is about the only other option), it seems like the way to go.

To get something like this going will take a lot of hunting in hobby shops and on the web. There are plenty of options and they all look very promising. I have not tried any of these myself with anything other than RC car battery packs. You would have to carefully check specs and ensure the charger is up to the task of charging your battery.

For a start, take a look at the Super Brain 959 from Model Rectifier Corporation which runs about $50 (same cost as most so-called "fast" chargers for bike lights). It's readily available online and looks like it's easily up to the task, featuring AC and DC input (so it'll run in your home or car), and all the features you need to effectively charge your batteries (adjustable current, adjustable voltage sensing down to .005V, etc.). This charger will work for 6V and 7.2V bike lights, but not for 12V or higher! When putting my mind to it, it seems unlikely that any of this type of charger will be able to charge a 12V battery.

Most modern bike lights have "MR-11" type halogen bulbs. "MR-11" is a generic designation for a bulb, where "MR" stands for "Miniature Reflector" and "11" is the number of eighths of an inch it is in diameter. Older bike lights used bigger "MR-16" bulbs.

MR-11 and MR-16 bulbs are commonly available from lighting supply stores and hardware stores (even Home Depot has them). Generally the minimum wattage of the widely available MR-11 and MR-16 bulbs is about 20W which is really the max you would ever want for a bike, and they are almost all 12V. They are available with a variety of beam patterns from flood to spot and all in between. They are typically marked with the angle, where 30 degrees is pretty much a standard flood and 10 degrees is a standard spot. These generic bulbs cost about $5-6 for an MR-16 and about $10-12 for an MR-11.

Now, onto bike lights :) You see, bike light systems don't generally use these "generic" bulbs. They use bulbs which are the same form factor, that is shaped the same, same size, same connector, etc., but they are usually custom filaments (voltage/wattage ratings) and sometimes custom reflectors. They typically cost more like $20 each from the bike shop.

Bike light bulbs are usually rated at 5-20W, common values are 5, 6, 10, 12, 15 and 20W.

So here's some useful info on these lights. The bulbs have some unique characteristics. These halogen lights were originally developed for household lighting for high-end homes like for track lights, micro-spot lights for pictures and artwork, etc. They would then run 8+ hours a day for years at a time, so they are usually rated at thousands of hours of lifetime. For a mountain biker who does, say, two 1.5 hour night rides a week for 16 weeks out of the year, that's bigtime overkill.

If you put "too much" voltage on the light bulb terminals, then some interesting things happen. The most significant effect is that the lifetime of the bulb decreases rather radically. If you put 10% more voltage than the bulb is rated for, then the lifetime is reduced to 1/3 of what it is otherwise. If you put 20% more voltage, then it's only 1/10 of the rated lifetime! Ouch! However, the rated lifetime is usually like 3000 hours, so 1/10 of that is still 300 hours, pretty good for a winter of mountain biking!

The other thing that happens is that the light gets much more efficient. This means it puts out more actual LIGHT and less HEAT using less POWER. This means that you might run a 20W bulb overdriven 20%, which results in a 24W draw on the battery, but as much light as a bulb rated at 40W would make normally. So you get 40W worth of light out of only 24W of power with a light rated at 20W, at the expense of bulb life.

This is known as "overdriving" the light. This is common in most modern light systems for bikes, and in fact it should be a prerequisite for ANY light you buy.

The other important thing about overdriving the lights is that the color of the light stays white longer into the discharge cycle. Let's say the bulb rated at 12V gets noticeably yellow at 11V. If you use a 12V battery, then it's going to droop to 11V pretty soon in its discharge cycle making you have to use yellow light for maybe a third or half of the lifetime of the battery. That stinks! However, if your nominal voltage is 13.2V, then it takes much longer to discharge the battery down to only 11V. In fact, a NiCD or NiMH battery will be flat dead before it gets this low. This means the light is useful for the entire charge time of the battery.

Now, there are a huge variety of useful bulbs out there and if you're clever you can do some mixing and matching. For example, there is one company making lights who makes a very attractive 10W single-light system with a good battery and charger, however 10W is not nearly enough light for trail riding. They say no other bulb will work with that system, but it's not true. Another manufacturer makes a 6V system which has 12, 15 or 20W bulbs. You can put the bulbs from manufacturer B into the lamp head of manufacturer A to make yourself a single-bulb, 20W flood light system.

So, most 6V bulbs out there for bike lights are actually rated at about 4.8-5V and overdriven at 6V. This is a Good Thing. They can be interchanged between different companies' light heads. Most 12V systems out there use regular 12V generic type MR-11 bulbs and either overdrive them with a 13.2-14.4V battery or just run them at 12 boring old volts :( However, these are all just advertised as 6V and 12V systems, but if you call the companies then they will tell you (or should, or you should not buy their product) whether it's overdrive or not and what the actual battery voltage is.

The point is, if you find a system that's a real bargain, has all the stuff you need, but has a 12W flood and 20W spot, while you think you need a 20W flood but that company does not have such a bulb available, you can probably use a 20W flood lamp bulb from a competitor's system to get what you are after.

These newer "Digital" light systems have got a light controller that does a couple of cool things. First of all, they typically have a good battery meter that tells you how much battery life you have left.

The other thing they do is switch between different output levels (voltages). What this does is give you variable light output and power consumption options with only one light (or two or whatever, point is, more choices than you'd normally have).

The way they do this is by "stepping down" the voltage going to the light according to how you switch it. You have, say, a 20W bulb and it might have 20W, 10W and 5W modes you can run it in. What this does really is starve the light of voltage so it draws less current and slows the rate of burn of the battery.

Now, remember about the color and efficiency of the light. If the light gets more efficient with more voltage, similarly it'll get less efficient with less voltage. It's the same radical logarithmic curve too. So a light that's rated at 20W, when run at 3/4 the voltage to make only 10W, will produce WAY less than half the amount of light, and that light it does produce will be very yellow-orange in color. Then stepping down another notch will be even worse!

These "digital" systems are more expensive but your money is probably better spent on a spare battery or on a system with a larger capacity battery or two real lights bulbs in it. The other thing is, that light controller thingy seems awfully easy to damage considering that it's digital and has to ride on a mountain bike.

Most bike lights are halogen lights. These are incandescent lights like you use in your house, but with halogen gas inside the bulb rather than being a vacuum in there. There's some technical reason why this is better but I forget what it is. It improves efficiency of the light bulb and maybe improves life or ??? Anyway, they're halogen :)

The way a bulb like this works is you have a thin wire called a "filament" which is connected between the terminals inside the bulb. When you apply a voltage to this, the wire gets hot and turns red or some other bright color and glows, this makes lots of heat and a little bit of light. To make lots of light requires a WHOLE LOT of heat. Since you don't need the heat, it's waste, so they're not particularly efficient.

There are other ways to make light. Ever seen lightning? Lightning makes light with no filament. It's called an "arc", this is where you apply a BIG voltage across some ionized gas (like air, in the case of lightning) and an arc, or spark, forms between the terminals. This makes light and heat, but, depending on the gas which is used as the medium, it can make much more light and less heat than a regular incandescent lamp.

They use Halide gas in these HID lights and a voltage converter to convert the measly battery voltage to a very high voltage to make the spark in a HID lamp.

The result is a very blue-looking light (which looks cool, but imho is not nearly as useful as a white light from halogen) that is much brighter for a given power output than a halogen light. They say you get about the equivalent of 40-45W halogen lights in terms of light output from about 20W or less of halide-arc lamp.

The bulbs don't last as long as halogen and cost about ten times as much. The whole system costs about 2-4x that of a similar halogen system. They're really bright! They're also really pricey. A regular 20W halogen is enough for the trail. Maybe if they came out with less expensive ones that used even less power (like say, 10W with equivalent to a 20W halogen) then it would be worth it for the extended lifetime of the battery.

I thought that too.

Let's add it up. If you believe me and have decided you need NiCd batteries, then you need probably 11 D-cell Ni-Cd's to make a 13.2V 3Ah battery. Those are about $2.50 each, so that's $27.50.

Now you need an old water bottle to stick them in. $1.50, cut the top off, tape the batteries together and spray in some spray-foam insulation to hold them still, duct-tape the top back on. You're up to $29.

Now you need a charger. Aw, heck. To make a charger, the best way is to use a DeWalt drill charger which is modified to plug into your battery and charge it. They work very well with Ni-Cads. About $50 for a new one, or about $30 on ebay for a used one. Say you get one on ebay, you're up to $59.

Now, you need two bulbs, one 12W, one 20W. Well, you can't get a 12W generic hardware store bulb, so you have to cough up $20 for that bulb from Nite Rider or some other bike light vendor. The 20W flood is easy to get from the HW store for another $10. Now we're up to $89 and we still have to figure out how to mount this thing, make a housing of some sort, get wire and connectors, put it all together, etc. In the end it's over $100 just in raw materials to make a 12/20W system with a 3Ah NiCd battery.

I know where you can get a complete, new 12/20W light system for just $79. There's a ton of them out there for just over $100. And for $150 you can get a super-slick system with a 6Ah NiMH battery and a smart charger, 12/20W.

Now, if you can settle for a SLA battery and use a motorcycle battery charger that you can get at Autozone for $15 to charge it, then you can probably beat the $79 price by a few dollars. However, the $79 system I will reveal in a minute has NiCd batteries and is already put together.

OK, now we talk about some lessons learned while on the bike.

I have ridden with four different systems. The first three were loaners. The first one was a dual system with MR-16 bulbs, a 20W spot light (10 degree) and a 10W flood light. This was not an overdrive system. The 10W flood light was not enough light overall for trail riding. It was just not bright enough. The 20W spot was also insufficient. It was too bright in the middle so it causes your pupils to adjust to the bright spot, and you still cannot see the edges of the trail very well nor see around any curves or over the top of hills. After trying this system, it became clear I needed a 20W FLOOD and perhaps a 10+W SPOT that I could aim further down the trail and turn on only on straight, fast descents. This system had NiCd batteries and the lights did not get any more yellow than they were to begin with as I used it, but they were noticeably yellow the whole time.

The second system was a Nite Rider Classic Plus. This was a very good system. 12V overdrive system with a 20W FLOOD light and a 12W spot. The downside to this system is that you cannot aim the two lamps independently. This system, unfortunately, completely quit on me 20 minutes into my second dark lap at my 24 hr race and ruined a lap. However, I can't say that there's anything wrong with them in general. The point is, the 20W flood light, overdriven, was perfect for most of the trail. The 12W spot was of limited usefulness since It could not be aimed to look further down the trail on straights, it just lit up the middle of the flood area a little brighter (you could barely notice it). This system had NiMH battery and the lights were bright, clear white all the time until it completely croaked.

The third I used was a home-made helmet light with a 20W/12V MR-11 from a hardware store and a giant SLA battery. This was heavy and kludgy but was loaned graciously from a neighboring team after the Nite Rider system croaked. I learned several important lessons while suffering through a lap with this one.

First thing is, a helmet light is really a necessity. It was so easy to turn my head and see around corners, which is a huge bonus you don't normally think about.

The second thing I learned, the very hard way, is that a helmet light by itself is completely inadequate. This is because you cannot see shadows cast on the trail, so you have very impaired depth perception and a very impaired perception of the trail surface. Let's say that bumps and drops in the trail were a very big surprise for me, so much that I had frequent wrecks. I felt like I was blind.

The third thing I learned is that regardless of how bright, when that light gets yellow, it might as well be off. The SLA battery was at fault here, plus the fact that this light was not overdriven.

Now I have my own system. A 5W Vistalite Code 5 helmet light (overdrive, NiCd), and a Marwi Pro Elite handlebar light with a 20W flood, 15W spot and an 8Ah NiMH battery (according to Marwi, not overdrive). This whole system cost just over $200 and will run about two hours. It only has overnight chargers and takes about 12-13 hours minimum to fully charge. The Marwi lights are individually aimable so you can adjust it so you can see way down the trail with the spot light on. I really believe you need a helmet light, low power so that you can SEE around corners but not so bright that it illuminates the shadows cast by your handlebar light, PLUS a handlebar light with a 20W flood and some smaller-wattage spot light that's independently aimable. FWIW, I have ridden several times with this system and I cannot recommend it more highly. The 5W helmet light is the perfect size and does not wash out shadows cast by the big handlebar light. It has enough light to aid in seeing around corners, to see your computer, your watch, your pedals so you can clip in, to see to make repairs to your bike or rummaging through your pack, etc., and also it illuminates low branches that have clotheslined a few of my friends when they rode under them with only a handlebar light.

Absolute dirt cheapest: Laser Edge

http://www.bicyclelights.com/new_page_2.htm

This is a 12V system that has a 2.8Ah NiCd battery and overdrives 12V bulbs. It has a 12W and a 20W narrow spot light. The 20W light bulb would need to be replaced immediately for a flood light, but 12V 20W flood lights are available for $8 at home depot putting the whole cost under $100. The system includes two spare bulbs. A friend has this set, and although they have not been trouble-free (defective bulbs), the customer service has been first-rate and he's very pleased overall.

Now, while that's the bone-dirt cheapest, the best value is probably either the Marwi Kamikaze or the Marwi Pro Elite:

http://www.marwiusa.com/www/lighting.html

They have them at http://www.universalcycles.com at affordable prices, although there are better prices to be had.

For $150 (or even $125 from one source), the Kamikaze has a 6Ah 6V NiMH battery with a 12W spot and a 20W flood. These have a gorgeous quick-release offset mount that works even with a beefy stem. Another $20-30 gets you into the Pro Elite which has a bigger battery (8Ah) and a bigger high-beam (15W instead of 12W). This is a system that uses custom bulbs. The bulbs have a bluish reflector that looks a lot like an HID light. Although Marwi told me they are not overdrive lights, they are as bright as, if not brighter than, Nite Rider's overdrive lights in a direct comparison. Marwi OEM's these lights to Performance Bike and Bike Nashbar who sell these systems or variants with their name on them. The Kamikaze is Performance Bike's top of the line light and costs $200 from Performance, a $50-75 premium over the Marwi price. Nashbar has the Kamikaze relabeled, but with a different battery-in-a-bag battery for about $180. Don't buy these ripoffs, get the Marwi elsewhere. FWIW, Marwi's customer service is also first-rate. They make an impressive, high-quality product at a very impressive price. Their 12W Elite helmet light is also killer and at under $100 is a good value.

There are other good values out there, particularly the Night Rover from Cygolite and some of the lower-end Cat Eye products, but they suffer from some problem such as SLA battery or non-aimable dual lights, etc., which knock them off the list. Also, they're not as good a value as either of these I have presented here.

I suggest you get these while they're still so cheap. My bet is they will rise in price to be competitive as the names catch on. The Laser Edge will probably end up in the $150 range and the Kamikaze will probably eventually fetch over $200.

As far as general tips on buying lights, the main thing is to determine what you need first, then cut through the mumbo-jumbo of the bike light industry hype and get down to the brass tacks. Bicycle lights are really pretty simple electromechanical devices that have specifications that are not mysterious or hard to understand. So before you go shopping, after having read this whole document and done some research you should have the answers to the following questions:

1. What's my budget?
2. How much power do I need?
3. How many lights do I need?
4. What kind of battery do I need?
5. Do I need a fast charger? [as if one even exists for bike lights without major ingenuity on the part of the user]

Once you answer all of these questions, then go shopping for lights and make sure you find a set that meets all of your requirements. For me, my budget was $200, I needed a 20W flood light and an additional spot light plus a helmet light, I needed three lights (2 bar, one helmet), I needed NiCd or NiMH batteries, and I wanted a fast charger and I wanted an overdrive system. I ended up compromising on the fast charger because there was no way to meet all of my needs in one set of lights, and I compromised on the overdrive part of the system because I saw that it made little difference in the lights I purchased.

When looking for lights, there are some real necessities which you should use to calculate whether the system is really adequate for trail riding.

1. Is the system an overdrive system? There is a real gain in efficiency to be had with overdrive lights.
2. Does it have a 20W flood lamp? The flood lamp is a near necessity for riding on twisty trails.
3. Does it have dual handlebar lights with a switch to turn on the high-beam separate from the other light?
4. Does the dual handlebar light allow independent aiming of the lights? This makes a really big difference.
5. Does it have NiCd or NiMH batteries? SLA is really not suitable for bike lights.
6. Does it have a smart charger? The almost-smart "smart" chargers from the higher-end bike light companies are absolutely the minimum standard for NiCd or NiMH batteries.
7. Does it have a quick-release mount? The last thing you want is to have to unscrew thumb screws and hardware to remove the lights.
8. Does it have a water-bottle battery (for bar mount)? The battery-in-a-bag types look like a real losing proposition.
9. Does the helmet-mount light have adjustable angle? If not, the likelihood of you getting it aimed in the right spot is extremely low.
10. Will it last a half hour longer than I expect to ride with it? If not, then you'd better be carrying a flashlight and have plenty of time on your hands.

This should get you started down the right path.

DIY Bike Light article: http://www.mcs.surrey.ac.uk/Personal/csx1jw/lights.htm

Light Brain Resources: http://www.geocities.com/sunsetstrip/concert/2301/index2.html

DORBA light system (this is the helmet light I borrowed at the race): http://www.dorba.org/scrapbook/earls_light/

Bicycle Lighting: http://www.audax.uk.net/lights/

Halogen Bulb Information: http://simon.trinhall.cam.ac.uk/bike/lights.html

Bulb Direct replacement lamps (bulbs): http://www.bulbdirect.com/search.asp

Reflectalite bulbs: http://www.reflectalite.com/halogenpage.html

MTBR bike lighting spotlight (REALLY GOOD!) http://www.mtbreview.com/spotlight/lights/

Note the Performance Bike system they tested is the same as the Marwi Kamikaze; they don't have a photo for the Marwi Pro Elite, but the Kamikaze/Performance light has just about the best light pattern of all of them in the review.

Mud, Sweat and Gears (dealer with great prices on lights): https://secure.max.net/cgi-bin/sform/bikeusa.com/index.html

I originally ordered my Marwi lights from these guys but they were out of stock. They were really reasonable and easy to deal with, even though I ended up getting the lights elsewhere. Their prices are fantastic.

Bikecurrent list archives: http://www.topica.com/lists/bikecurrent/read

Bikecurrent is a mailing list where they discuss bike lighting a lot. Many very knowledgeable people there, LOTS to learn.

Laser Edge Lights: http://www.bicyclelights.com/new_page_2.htm

The cheapest useful lights on the planet. $79!