Editors Note: This is the second installment in a series on Grannygear’s experiences in building his own LED light set for mountain biking. Remember, this isn’t tinker toys here, you can get seriously injured if you don’t know what you are doing. So if you are not sure about your electrical knowledge, it is best to leave this sort of thing to the pros. That said, read on for Part Two of Grannygear’s DIY LED light build.

Light my World DIY Style: Part Two – Ya gotta have a good plan.

So, now you have made the decision to forge ahead bravely into the night with some spiffy new DIY lights. But first, you need to figure out what you want to end up with and what parts you need to get there.

Points to ponder:

#1- How much light do you need? You can build a really, really bright light that will sear the retinas of unlucky victims but it will cost you more in $ and effort. I wanted to be able to have enough light for moderate speeds on fireroads and twisty singletrack. It seems like 200 lumens is a beginning point to be able to ride off road at a trail pace. 400 lumens are what I built for on the bars. I added another 200 lumens on the helmet. Other things to consider that are related are the light pattern, flood or spot based on the optics (lenses) that you use. Typically there is a blend of both flood and spot in a light build.

#2-Do you care about multiple levels of light or strobe modes, etc? If you commute or spend time in traffic, you may want a flashy-type light setting to get folks attention. You may want to be able to turn your light level down for long climbs, rest stops or to prevent a bit of night blindness where your eyes adjust to the brightest light setting over time and then a fast section of trail seems like the high setting is not enough.

#3-Where do you want the light to be located…bars or helmet or both? The general thought is that if you have to use only one light, put it on the bars. There is one really good reason for that. If the only light you have is on your head, the angle that the light hits the ground washes out all the detail in the trail so it all looks flat. Imagine a light pointed straight down at the ground from above. It would cast no real shadow. Bumps, rocks, small trail imperfections all go away. A lower angle of the beam on a bar mount casts shadows that tell ya’ a lot about what is coming up. But, on the other hand, a helmet light allows you to point the light where you are looking. This is great for twisty singletrack, drops into ravines, working on your bike and looking to see what that scary noise was off the side of the trail. It also is always pointed where you are looking so if you turn and talk to another rider, you will blast him or her. I hate riding with just a helmet light, but that is me. I want both, but if I had to choose just one, it would be a bar mounted light.

#4-How are your fabricating skills? This is not rocket science or master level builder skills here, but you will need to drill, cut, sand, grind, solder, strip wires, glue, etc. Most basic hand tools can suffice. You are only limited by your imagination and resources. Cruising the lighting forums, you will see everything from plumbing parts to CNC’d uber-lights. But, the total execution is more important than how blingy it is. You can build a great light out of simple materials.

Once you have an idea on how much light you need/want and, what kind of housing you want to create, you need to come to a shopping list of parts. The major parts are:

The LEDs. The major players are the Cree and the Luxeon series of emitters.

pic from www.ledsupply.com

It seems like the technology has been leap frogging from one month to the next as each new bin (the series or generation of each new LED) raises the bar for lumens at a given current level, Vf, and light temperature (how white or not-white it is). Now there are multi LEDs on one star, 3 or now even 4 emitters on one device. When will it end? Who knows? But, there is no reason to buy a much older generation of LED as the relatively recent ones are still inexpensive. I paid about 6 bucks each for a recent bin, Luxeon single emitter LED that puts out around 200 lumens at 1000mA. I suggest buying LEDs already mounted on a star like the above picture shows…much easier to deal with.

The optics. LEDs like lenses more than reflectors, although there are reflectors as well. The optics are pretty cheap, so it is easy to play around with different lenses to see what you like best. Generally speaking there are spot lenses and flood lenses, spot being a narrow light pattern and flood a wider pattern. As well, not all optics are made for just any LED, but can be specific. Some folks are even making their own out of acrylics.

pic from www.luxeonstar.com

The drivers. An LED likes to see a constant voltage. Obviously your batteries will tend to provide less and less voltage as the night goes by, so a solid state device that sits between your battery pack and your LEDs will keep that voltage as constant as it can, at least until the voltage drops below what it needs to run. There are two basic types of drivers…buck and boost. As well, some drivers are very cheap and simple, some will provide multiple light settings including strobe settings, etc. The choice of driver also relates to the voltage requirements of your string of LEDs and your battery pack size. This magic formula is a bit beyond the scope of this article, but it all needs to blend well to end up with a happy light. I suggest you read a lot of forum posts and get the info you need. I chose a blend of drivers. For the helmet light I will use a very cheap and small (nickel sized) driver that will supply 800mA to the single LED. For the twin bar lights, I used a more costly single Buckpuck 3023 @1000mA with a dimming circuit so I could have a 50% setting for the bar lights.

pic from www.ledsupply.com

The batteries. It makes a lot of sense to use the new Lithium Ion batteries as they are tiny, powerful and easy to charge. There are some issues with some battery types in extremely cold weather as well as some battery types can go into a thermal runaway kind of scenario and catch on fire. Be careful. The most popular type of pack for a multi LED build seems to be a 14.8 volt Li-Ion pack used with a smart charger and a battery protection circuit. Lithium Potassium batteries are out there but require even more attention to keep them safe. I chose NiMH batteries for several reasons.

I already had a fast AA and AAA charger so I bought a 20 pack of 2300mAh AAs which was enough to build 2 lights + for less than I could have bought a more costly Li-Ion pack for one light. I can use the AAs for other stuff around the house and it is easy to replace a bad cell.

They represent a reasonable compromise on size/cost/availability and are easy to deal with. I will accept a small weight/size penalty for this decision.

Finally, there is the container for all that stuff. Aluminum is the material of choice since it weighs very little, is easy to drill, file, manipulate, etc. and it is a great thermal conductor. You see, these high power LEDs get real hot when they are running at a high current level. So, part of any light build has to be how to deal with conducting the heat away from the LED. That is why there are no PVC pipe builds going on, but there are plenty of aluminum tubing lights out there. Heat sinks can be added, but the trick is to have the surface that the LED is mounted to be able to carry away the heat into the housing of the light and then into the air. Otherwise, your light will have shorter life than you planned.

Source list of parts suppliers: There may be more than these and I suggest that you do your homework before ordering.

http://www.ledsupply.com/index.php

http://www.cutter.com.au/index.php

http://www.dealextreme.com/

http://theledguy.chainreactionweb.com/index.php?osCsid=4b57050f42a08102f67b324b4af498a3

Next we will get into the building of a set of flashlight based lights and how it turned out, what it really cost, what I learned, and whether it is all worth it. Stay tuned for Part Three.