3 Watt LED Bike Light Experiments
June, 2008, Rev f
Michael Krabach

Contents

Introduction
Synopsis of Experiments
Prototype 1 - Resistor Controlled Prototype
Prototype 2 - Triple Cree with large heat sink
Prototype 3 - Double Cree with Individual regulators
Prototype 4 - Single Cree and regulator
Prototype 5 - Single Cree and regulator
Prototype 6 - Triple Cree revised heat sink
Prototype 7 - Triple SSC in C Mag-lite Head
Prototype 8 - Triple Cree in D Mag-lite Head
Prototype 9 - Prefabricated 3 LED Mag-lite Head
Prototype 10 - Red flasher with Wide Optic Lens
Prototype 11 - Yellow flasher no Optics
Prototype 12 - Red flasher no Optics
Prototype 13 - Red flasher two LEDs
Prototype 14 - Triple Cree with 8 deg Optics
Prototype 15 - Red flasher two Cree LEDs
Prototype 16 - Red flasher two LEDs Clear Case
Prototype 17 - Auto 12 v clearance light
Light and Beam Measurements
Conclusions, Recommendations, and Further Speculations
Summary Table and Parts Sources

Conclusions, Recommendations, and Further Speculations

With the availability of the Internet it is becoming very easy to make your own bike light, even if you only have hand tools and a soldering iron. The rational of this experiment is to present builders with ideas, and to show that it is possible to economically build a good bike light. With commercial models ranging from $100 to $900, a hobby builder can put together an excellent bike light for much less. The three 3 watt Cree prototypes 2 or 6 cost me about $45 for parts. Prototype 5 cost about $15. The batteries cost about $20 for the 12 volt gel cell, about $8 for an alkaline lantern battery, and $9 for 4 rechargeable NiMH AA batteries. A good charger for the 12 volt gel cell is about $30, and a good charger for the AA batteries is about $40. The AA charger is useful in itself because it is a good investment for other AA electronics around the house or shop.

In constructing the various prototypes I came to the following conclusions.

Heat dissipations is always a consideration. Plastic housings can never be used unless some type of heat sink is exposed to the outside. The Mag-lites heads are nice looking but I am not sure of their ability to dissipate enough heat without degrading the LEDs. The D unit has about 1 oz more metal and is more open in the back. It also has more tri-optics that fit in the assembly. I found that the aluminum angle stock gives a much better heat sink arrangement. The angle material has more surface area per unit weight than the Mag-lite prototypes and you can make the units as wide as you like for any number of LEDs. Cutting and epoxying the pieces together is fairly easy.

Mounting the LEDs in proper position is most difficult on the handmade heat sink slug for the Mag-lites. Getting the LEDs aligned and bonded on the slug is a pain unless you do something like Prototype 9, with the pre-assembled triple LED module. But if you use the tri-optics, there is no problem wiring up the LEDs. When mounting LEDs on the angle stock and using the L2 Optics, you have the difficulty of having to file notches in the bottom of the plastic optics for wiring channels. Other optics that do not have the broad base of the L2 optics (cone shaped individual prisms or reflectors) are easily wired but you may have to consider alignment of the optics.

The L2 optics seem to utilize the LED beam patterns better than the tri-optics. The ability to clip on different sub-lens diffusers is a good feature even though you loose about 15% of your light.

Mounting the lights is easier and much cheaper using the plastic spring clamps than commercial clamps or hardware hose and pipe clamps.

The gel cell lead-acid 12 v batteries, the 6 v alkaline lantern batteries and the NiMH AA batteries have been found to be acceptable along with any charger units. If you want to save weight and pack more power, consider the Li-ion rechargeable batteries, but do a little reading up before you use them. Look carefully at the LED driver module input and output voltages, especially if you are considering using any of the DX modules. I like the bFlex driver for the programmability and size, but would recommend the wired Buckpuck with a potentiometer for simplicity and versatility.

While obtaining
parts from local suppliers and Internet dealers in the US is fast, getting some of the critical parts (LEDs specifically) from Hong Kong will take time. Currently (Feb. 2008) obtaining parts from Hong Kong (DX Extreme and Kaidomain) may take several weeks to arrive, and then you may only receive a partial shipment. The parts from Hong Kong appear to indicate what large manufacturers are starting to use for lights, or parts that were prototypes for manufacturing, or even items that were left over from manufacturing. So the specific parts referenced in this article may be not available or out of date in a year. I have not found a good source for the newer LEDs in the United States so that is the bottleneck in building these bike lights.

As for a recommendation for a front bike light, I think the Prototype 5 is ideal for an emergency light that can be carried with 4 AA batteries if there is a possibility that you will need to continue biking after dark. If you plan on commuting or riding after dark, Prototype 6 offers nice flexibility being able to change the optic sub-lens to change the beam pattern. I recommend Prototype 8 for riding on mostly city roads that are straight and you want to keep your beam concentrated on the side of the road, and also eliminate blinding oncoming auto drivers. I find the tri-optic lens DX SKU-1912 (seen in the Light and Beam Measurement section) perfect for straight riding. The beam is just wide enough to cover a wide road shoulder, and reaches out 80 feet or more with enough brightness to see hazards in the road. Change the tri-optic lens to the DX SKU-1911 and you have a beam that is perfect for riding winding trails or bike paths. (I do also use a modified AA flashlight using a 3 watt Cree LED running at 500 ma on my helmet to assist night riding when I need to see to the side. A suitable off the shelf AA flashlight, running at 1000ma, about 1 1/2 hrs, is the Ultrafire WF-606A, DX-SKU-4238).

After building the six rear flashers, the most convenient is using an old VistaLite VL500 (or VL300) light for the case. There are multi-mode controller/regulators available that uses a single AA battery and have memory for last mode used. While the L2 optics and sub-lens diffuser on prototype 10 gives a somewhat flatter beam than prototype 12, I could not find a convenient case to house the LED, L2 optics, battery and controller. So I recommend using an old VistaLite case if you have one. In all probability you will not find any old Vistalites. Prototype 16 was the result of a search for a commercial flasher (or housing) that is cheap and (more or less) readily available. This version has no lens to direct the beam and so the beam is a lamberton distribution, very wide. But the point source of the LEDs are quite brilliant at a distance down the road. Using the police (warning) mode gives a distintive pattern that stands out among the traffic. So Prototype 16 can be recommended if you want to build a powerful rear bike flasher for about $15. For extra brightness use the red Cree LEDs as opposed to the generic red LEDs. All the parts can be ordered from dealextreme.com.

Prototype 10 construction in sealing the L2 optics to the star LED indicated that there may be a problem in using GE Silicone II adhesive to seal the units. All the other prototypes that used the sealant seem OK, but I use now a urethane glue to seal the L2 optics to the star LED.

There are many ways of building your own bike light as more parts and ideas become available. I hope to continue to add to this article as new prototypes are built.