Functional lighting for bicycles has always been of particular interest to me. My previous article on the subject, from several years ago, was mostly to do with incandescent light sources, since that was pretty much all that was available at the time.
LEDs have been around considerably longer than that, but it's only been a couple of years since white LEDs became reasonably affordable, at a useful level of light output. While a bike headlight is necessary for seeing what's in your path at night, the most important reason for having one is to make you and your bike more visible to motorists. The more light, the better.
The traditional flashlight-bulb-powered-by-a-couple-of-flashlight-batteries type of bike headlight is pretty much worthless for any purpose other than decorating the bike. In this article, I will cover what's required to either convert a traditional bike headlight to more powerful and efficient LED lighting; or to build one from scratch, to your own design.
For our purposes, there are three types of white LEDs to consider: High-Power, in which a small number of LEDs are used, Mid-Power, in which a larger number are required for similar brightness, and Low-Power, in which an even larger number are used.
Typical Low-Power 5MM white LED
Low-Power white LEDs have been around longer, and are what most people think of when you say LED. Their main advantage is that they draw very little electric current, which is why LEDs became so popular, so quickly. An LED will deliver much longer battery life than an incandescent bulb, even of the small flashlight type. The drawback is that a single Low- Power LED doesn't produce nearly as much light as a bulb.
The example shown above produces 1,100 millicandelas at a 100-degree angle of view (2.469 lumens). A typical 100-watt light bulb, in comparison, produces 1,700 lumens. However, the lumen rating of a light source has a lot to do with the angle of view. The typical light bulb has an angle of view of over 300 degrees without a reflector. If the LED example had the same angle of view, its lumen rating would be 12.897 lumens; so you can see that comparing lamps and LEDs can get complicated. I prefer the empirical method: eyeballing light cast on a wall.
Typically, a White Low-Power LED will draw 20 to 30 milliamps at 3.5-4 volts. A typical flashlight lamp in the same voltage range will draw approximately 15-20 times more current (300-400 milliamps). To achieve the same light output as the bulb, you can use more LEDs, however an array of fifteen 20-milliamp LEDs will draw almost as much current as a flashlight lamp, as the current draw of each LED is multiplied by the total number of LEDs. However, by choosing the right number and type of LEDs you can gain much longer battery life, in addition to one of the best LED features: longevity. LEDs are typically good for 50-100,000 hours of operation, and are almost indestructible, since there is no fragile glass envelope or flimsy filament involved.
There are numerous variations in Low-Power White LEDs. By choosing the right type, you can come up with a good solution for your lighting needs. Even within the category of the 5mm package (T-1 ¾) above, there are many levels of light output and angle of view; and other packages have equally broad power/light levels and angles of view. In theory, the narrower the angle of view, the longer the throw of the light beam. However, narrower-beamed LEDs tend to throw a more intense center spot surrounded by a less-intense surrounding nimbus, which rapidly falls off with distance. Wider-angle-of-view LEDs throw a more even field of light for a shorter distance, but the beam can be extended by the use of a lens for narrowing the beam, which can actually make it more effective for head-lighting purposes. This is closely analogous to the use of a reflector with an incandescent light bulb.
The example at left is twice the size of the previous type. In many examples, it is more powerful, although you could probably find a more powerful 5MM LED than some 10MM examples. Reading the tech specs is the only way to actually know, and even then, an actual test is the best way to compare. The example shown at left, in the Radio Shack catalog, is called "10MM Ultra-High Brightness White LED". It has an output of 28,500millicandelas at an angle of view of 10 degrees. Converted, this gives an approximate rating of 0.681 lumens, although its output, in theory, is many times higher than the smaller and less-intense example above it, but which has a higher lumen rating. This is due to the narrower angle of view.
Other Low-Power LED package types:
10mm "Ultra-High Brightness" White LED.
(Right) 4-pin Wide Angle "High Brightness" White LED
This is an interesting type with good potential in many ways. It is rated at 600 mlm (millilumen flux, which I think translates to 0.6 lumen). As with the previous examples, it draws 20 milliamps at 3.5-4 volts. Its angle of view is 130 degrees. It gives a very bright, even wash of light at fairly-close distances, which may be controlled and improved for our purposes, by an external optical element. The square package has an added advantage, in that it can be packed edge to edge in a larger array, which would be needed anyway for adequate headlight power, for a Low-Power LED type.
4-pin Wide Angle "High Brightness" White LED
This tight-packing possibility makes the array look almost seamless when lit, like a photographer's diffused "soft-light box". This can be a quite striking look when positioned on the front of a bicycle, which gives good kustom styling possibilities. Since arrays based upon this square module are either square or rectangular in shape, it considerably simplifies making a housing for such an array, permitting the use of bent and fabricated sheet metal or fabricated and glued sheet plastics or composites.
This type of LED package, along with others, lends itself to use with plastic fresnel magnifying lenses, commonly and inexpensively available for use by the far-sighted (hyperopians), in magnifying book text and restaurant menus. As these lenses are plastic, they are easily trimmed to needed size with scissors or tin-snips. As usual, experimentation should establish suitability and the number of units needed.
All of the above types are ones with which I have actually worked. I found them all at Radio Shack, which is quite convenient for me. However, any type of LED found in the parts drawers at Radio Shack can be obtained much more inexpensively on-line from other sources, such as Digi-Key Electronics. Radio Shack's pricing for the individual examples is comparatively expensive. For example, the 4-pin device shown above costs US $2.39 at RS. When I find a type I like, as a result of experimentation, I can order it at a much better price, especially in quantity. A virtually-identical 4-pin LED, manufactured by top-of-the-line manufacturer Cree, costs only $0.65 from Digi-Key, with considerable discount for larger quantities.
Ebay is also an excellent place to find good prices on many types of LEDs. For a commercial prototype home lighting project, I recently ordered 100 pieces of an extreme wide-angle type of white LED for the price of $15.95, which works out to $0.16 each. If I'd wanted 5000 of them, I could have gotten them at a nickel apiece. To see the huge range of types available through Ebay, run a search for "White LED".
Ebay is also a good source for LEDs which haven't made it to this continent through usual channels yet, such as a new generation of "Middle Power" White LEDs being sold out of China.
At Left are seen a pair of 10mm LEDs which have just recently shown up on Ebay, priced at 30 units for $17.99, with free shipping from China to North America. They draw 100 milliamps each at 3.5-4 volts, and are rated at 280,000 millicandelas at 40 degrees (106 lumens). This is quite impressive, and it wouldn't take very many of these to make a very effective headlight, bearing in mind that the individual current draw is multiplied by the number of units making up the array. Still, five of these in an array, while drawing approximately the same amount of current as a flashlight bulb- 2.5-3 watts, will produce much more usable light than the bulb. I haven't tried this type yet, but it's well worth giving a shot. A further advantage of the Mid-Power LED types is that they don't require external heat-sinking. Notice the prominent "ears" in the power leads, below the transparent packages. Those are small heat radiating surfaces, for air cooling.
Mid-Power White LEDs
The advantage of Low and Mid-Power LEDs is their comparatively-low current draw, relative coolness of operation, and fairly low cost per individual unit. However, the need to use fairly numerous individual LEDs to produce relatively bright lighting can result in a slightly bulky light source. This is problematic when retrofitting an existing headlight with LED illumination.
High-Power White LEDs:
For that task, the best choice is probably the High Power White LED. An earlier example, from several years ago is shown at left:
This is the Luxeon Star K2 LED. It draws 700 milliamps at 3.5-4 volts, and produces 75 lumens of illumination. The Dave Gibson Amish Buggy Headlight I use on my "Heat"chopper has six of these K2 units in its housing. The array produces an amazing amount of light- 450 lumens!
This mount type is called the Star due to the shape of its modular mounting plate, which is 20mm across. The holes radiating around the edges correspond to 4-40 machine screws. This diameter is almost the exact size of an American 5-cent coin (nickel). Any time you pump 700 milliamps of current into a single small electronic device, such as an LED, you are going to get heat. While LEDs are immune to most physical abuse, they can be overheated; and failure to keep them relatively cooler than their critical temperature point (approximately 150 degrees centigrade) will result in a significantly shortened lifespan. The Star mounting plate is made of aluminum, which has excellent heat-transfer properties; but this is not an adequate amount of heat sinking for extended periods of use at this energy level. So, the Star plate is commonly mounted to a larger metal surface for sucking away the heat produced by the unit. The Luxeon Star K2 is still available, for a very nice current price ($7.99 each).
Luxeon Star K2 LED
While my Dave Gibson headlight produces plenty of light from its six Luxeon Stars, with the necessary heat-sinking, it's quite a bit larger than many existing bike headlights, so cramming that many into, for example, a typical chrome bullet bike headlamp housing, would be problematical. I had a similar problem with a recent project: retrofitting an antique acetylene bike headlamp with serious LED illumination, for BRK North American Associate Editor John Brain.
LUXEON Rebel High-Power White LED in Tri-Star mount:
The lensed light chamber (left side), where acetylene gas was burned to produce light, is approximately the size of a modern chrome bullet light, so there really wasn't enough space available for a lot of any sort of LEDs, much less Luxeon Star K2s.
Fortunately, technology continuously advances. Now we have available the Philips Luxeon Rebel LED line, which is just as, if not more powerful than the K2, while being considerably smaller. Below is shown a size comparison of the Luxeon Rebel and other comparable light-power White LED units currently available:
Antique acetylene bike headlight
Luxeon Rebel (far left) compared in size to equivelent LEDs.
3 Luxeon Rebels
The Rebel, shown above un-mounted at far left, is smaller than the nail on my pinky finger; and I have smaller hands than most guys. Left, the Rebel is shown in close-up view. Due to the Rebel's small size, three of them can be mounted onto a single 20mm Star modular mounting plate, as seen below left:
While sharing the same electrical characteristics: 3.5-4 volts at 700 milliamps, Rebels are available in several light-power outputs. Tri-Star modules range from a cumulative 285 lumens at $14.99, all the way up to 540 lumens for $38.99. I might note here that the Rebel Tri-star 540-lumen module, still the size of a nickel coin, puts out a hundred more lumens than my fairly large Dave Gibson headlight. When offered the choice, John Brain, being a hot rodder type, went for the maximum. Being of the same type, I was thrilled with his choice. "Too much ain't enough" and all that.
"Too much" pretty well describes this little monster. It is so intense that it can cause at least temporary vision damage if viewed dead-on at close range for a moderate length of time. Even viewing it at oblique angles for short periods during testing, I was left with residual floating after-images lasting 15 minutes or so. While doing web research on the subject of eye safety, using the search terms "Blinding Light", I found several patent applications for light-weapon devices and an actual product. The product is an accessory for mounting on a handgun. It is designed to blind the enemy before you shoot him, presumably.
I guess it makes sense, as light travels much faster than a typical bullet. Whether the blinding is permanent or not, hardly matters if it's followed by a bullet. As a side note: the "Blinding" handgun accessory light has only ONE Luxeon Star LED, rated at "only" 80 lumens. Since the highest-power Rebel Tri-Star module is 6.75 times more powerful than that, you may consider yourself warned, Mmmkay?
From my research on this subject, I'm considering making a piece of "Defensive Jewelry", based upon the Luxeon Rebel Tri-Star for my daughter, who has a normal "20-something" social life in NYC, which means being out and about late at night, in an urban environment.
As the Rebel LED is of the "Lambertian" optical type, it has a very wide angle of view (130 degrees). This is not ideal for a headlight, as it won't carry as far as a tighter beam. Fortunately, sources for the Rebel Tri-Star module usually carry a nice little accessory optic made of Lucite, specifically designed to be fitted to the Star mount.
Looking like a very fancy crystal version of the little 3-legged plastic gizmo used in the center of pizzas delivered in boxes, it gives a 25-degree angle of view to the light output, which is pretty much ideal for bike headlight applications. It typically costs $4.99 and is well worth it. Of course, if you have a box of glass and plastic lenses you've collected over the years, like I have, you might be able to find one you like even better. Plus, it's fun to experiment.
Working with LEDs is not exactly rocket science. Except for a few considerations, it's hardly trickier than hooking up a light bulb. First of the considerations is polarity. LEDs work off DC current, as delivered by batteries, and they have a plus side (+) and a minus (-) side. Hooking them up backwards can destroy the device. I speak from long experience, and many bonehead mistakes. The diagram below shows polarity indicators for T- type and 4-Pin package LEDs. High Power LEDs, such as the Luxeon Tri-Star modules have little pluses and minuses printed beside each electrical contact, making them fool-proof, except, maybe, for fools like me.
The second consideration is the need for a current-limiting resistor in almost every case. The value, in Ohms, of this resistor is determined by the current rating of the LED, its forward voltage, and the voltage of the electricity supply powering the circuit. Without a resistor, the LED can be destroyed by excessive current. This is especially so when the supply voltage is higher than the forward voltage of the LED. Most LEDs can be briefly "over-amped" without damage, but for longer periods, damage or destruction from heat will be done. Ohm's Law is the formula for determining the amount of resistance required for a given set of factors.
I've always had trouble with formulae, which is one of the main reasons my childhood ambition of becoming a rocket scientist remained unfulfilled. Ohm's Law is almost the simplest formula there is, but I still can't remember it, and always have to look it up. Even with it in front of me, just plugging in the numbers and doing the math is always
problematical for me. Imagine my surprise, when I recently discovered that there are on-line "calculators" dedicated to solving Ohm's Law calculations in determining the value of a current-limiting resistor for a single LED circuit easily. Here is one: http://led.linear1.org/1led.wiz. For determining current-limiting resistance for a multi-LED array, here is another: http://led.linear1.org/led.wiz. There are two ways of wiring multiple LEDs in an array. One way is Parallel, in which each LED is arranged
side-by-side with the others, with common pluses and minuses. The advantage of this is that the individual forward voltages of the LEDs are all the same as the individual LED's. This is good when your supply voltage is barely more than the forward voltage of an individual LED. Three rechargeable batteries wired in series deliver 3.6 volts. Most white LEDs have a preferred forward voltage of 3.5 volts. In such a situation, the current-limiting resistor is usually 1 ohm.
If your supply voltage is equal to or greater than the cumulative total of the forward voltages of all the LEDs, you can wire them in Series, in which the (+) of one LED is joined to the (-) of the next, and so on. This allows the use of a single current-limiting resistor for the whole string, which simplifies things considerably. The LED Array Calculator gives you your choice of Parallel or Series hookup, will show you a schematic or wiring diagram of the circuit, and even show you the color codes of the resistors. It will also suggest the wattage requirement of the resistors. Low Power LEDs can usually get by with 1/8-or ¼-watt resistors, High Power ones generally require 1 watt or greater rated resistors. For small quantities of typical resistors, Radio Shack stores are a decent source, as they're pretty cheap no matter where you get them. If you need a larger quantity of the same value, it's much cheaper to get them from a source like Digi-Key. Radio Shack has a very limited selection of 1-watt resistors, so a source like Digi-Key is usually better for those, also. I often buy them on Ebay, as well.
Dave Gibson Headlight
Heat sinking is an important element in designing a headlight with High Power LEDs. Low Power ones run much cooler, so they don't usually require a heat sink. I'll discuss the particulars of designing the heat sinking for a High Power LED circuit in the next part of this article- the "hands-on" documentation of a couple of projects. The basics are that there are two types of cooling methods: conduction and convection. Most solutions incorporate both aspects, with conducting the heat produced by the LED into a piece of metal, with an attached radiating element to transfer heat from the metal into the air.
The battery pack for powering a headlight is obviously pretty important. Considering the
Current pricing of brand-name Alkaline cells, I've decided that rechargeable is the way to go. NiCd (nicad) batteries are very inexpensive now, and chargers for them are simple enough that I'd usually build my own. However, since NiMh (nickel metal hydride) cells have much higher capacity (milliamp/hours) for the same-size package, and have become much more reasonably priced, I tend to recommend them. They require a more complicated "smart charger" to properly and safely charge them, but that type of factory-made charger is also much cheaper now (around $20). The long life of NiMh cells and their being hardly more expensive than a couple of sets of non-rechargeable alkaline cells makes them hard to beat.
In my opinion LiIon (lithium ion) batteries are expensive, and they still have a nasty tendency toward bursting into flame while charging. While they have an even greater capacity than NiMh cells of a given size, I don't think they're the right choice for a home-made bike headlight power supply, yet. So, I won't be dealing with those, at this point.
LEDs are normally soldered into place. However, when you're experimenting to see how many of a given type you'll need to do the job, that isn't very practical. For that purpose, I recommend a prototyping board (breadboard). They're available from almost any electronics parts source, including Radio Shack stores. As usual, RS is more expensive, but the things last forever, so the price difference is pretty much immaterial. RS gets $7.99 for a board. Below left is shown a typical example:
The sockets covering the board are spaced to match the pin spacing on IC chips and other electronic components, such as LEDs. Looking at the board in this photo, you'll notice that there are two narrow vertical rows of two sockets on either side. These are normally dedicated to power supply, with (+) on one side and (-) on the other. All sockets in those rows are electrically connected to each other. The two wider rows toward the middle of the board, separated by the wide groove, are electrically separate from each other. Within a given vertical row, however, all horizontal rows of sockets in a line are electrically contiguous.
In use, an LED is plugged into the board, with the (+) leg on one side of the wide center groove and the (-) leg plugged into the other side.
A wire jumper is plugged into that horizontal row, and into the power row for the same polarity. The same applies to the other side, except the current limiting resistor is used instead of a wire jumper. The resistor can be used in series with either leg of the LED, although the (-) side seems to be traditional.
A large number of LEDs can be plugged into one board for experimentation, then removed without damage. Radio Shack and other sources carry fiberglass circuit boards perforated with holes of the exact same spacing with copper foil pads surrounding the holes; so once you've prototyped your LED array on the breadboard, it's very simple to transfer components onto the perforated circuit board in the same layout pattern and solder it in place. The last time I was at Radio Shack, I noticed that they now have a circular circuit board of what looks very close to a size which might fit into a chrome bullet light shell. But even a rectangular board can be trimmed to whatever shape and size you want, with tin snips or kitchen shears.
Any electronic construction involves soldering. My recent High Power Headlight Retrofit project for John Brain has shown that it would be good to have the use of three different soldering irons, for various aspects. Ideally, here are the three types you would use:
For fine work, a 15-watt grounded tip iron is best. This is perfect for soldering LED leads. Heat from soldering can damage an Integrated Circuit chip or LED if too much heat is used for too long a time. The needle-nosed tip helps in soldering in tight quarters, too, as in the Luxeon Rebel Tri-Star module's solder pads, which are quite close together.
The 45-watt soldering iron is good for joins involving larger amounts of metal requiring more heat for a proper solder join. I use this one most often. If you can only afford to own one iron, this range is the one to have.
I actually own a dual-range high-watt soldering gun. The one below delivers 230 or 150 watts. I don't need this much heat very often, but when it came to soldering resistor leads to a heavy copper heat sink, I really needed it badly. Unfortunately, I use the thing so infrequently, I couldn't remember where it was hiding out in my place. I did the best I could with the 40-watt unit, but the joins weren't as perfect as I'd prefer.
My electronic engineer/upstairs neighbor/friend Willy also owns one, but he couldn't find his either, when I asked to borrow it. For something like this, it's always best if you can borrow it from a friend, relative, or neighbor, as they go for about $30.
I could write an entire article on soldering techniques, but I don't want to get into it now. There are excellent on-line tutorials on the subject; so Google the subject if you're a total nimrod at it, or check this one from Make Blog.