Bicycle Lighting - White LED Light
Bicycle Lighting - White LED Light
The construction below is for the newer, simpler, brighter MkII version, which is a 4-LED design. At the latest prices (late 1999) this can be built very cheaply indeed - good bright white LEDs are available for little more than £1 each.
The Knightlite Koncorde white LED light is a very good light - my only criticism might be that it is quite directional, but it is certainly the best commercial LED front light that I've seen. But this homebrew design (either the MkI or the MkII) is in a different league ...
How bright is it?
My own first impression (of the MkI, May 1998), just standing back from the parked bike a little, was that it was by far the brightest thing of its kind I had ever seen, just like a little supernova hanging on the handlebars. What was more the bluish-white colour was very strong and distinctive in the predominantly yellowish environment of road lighting.
It’s more important to evaluate a visibility light of this sort from a distance - 50 or 100 yards away, which is where this kind of light really has to be at its best. So I mounted it on a straight handlebar alongside a 10W HOT Vistalite and my usual modded yellow 5-led front light - then I took a little walk.
From 100 yards, and on axis - the white LED light and the yellow one (in steady mode) appeared equally bright. This is in some ways remarkable as the same catalogue specifies the white LEDS as 1cd brightness and the yellow ones 12cd. However, the colour of the white light was superb, much better than the yellow. On this basis the white light was the winner.
The yellow light, being based on a commercial design, could be switched to flashing mode - that improved visibility greatly and made it a clear winner. Of course the 10W HOT halogen bulb was magnitudes brighter than either of the LED lights - until I moved off axis. This was the acid test.
The 10W halogen bulb lost impact almost immediately and became less bright than either of the LED lights. This of course is how cycle lights are normally viewed by oncoming traffic, as the main beam is pointed down at the road. Quite soon after losing the 10W, the yellow LED light practically vanished. Use of flashing mode improved things a bit, and brought it up to a visibility level similar to the 10W off axis - still a bit disappointing. These yellow LEDS are specified as 4º angle of acceptance, though the KnightLite plastic lens may improve this slightly. The new white LED light simply did not change. Within the confines of a normal suburban road at 50 yards range, I could not get off axis sufficiently to affect the visibility of this light. These LEDS are specified as having a 60º angle. This is a great commuting light.
In summary, this 5-LED white light was a real advance in conspicuity especially in lit-road and commuting situations. On the open road, at long range, I think that the flashing yellow LED light still has the edge. Of course, a flashing white LED would be even better, but I was unable to engineer this - and in fact the Knighlite Koncorde in flashing mode is rather disappointing, it works much better in steady mode.
Construction - the MkII version
This new construction uses 4 LEDs and is substantially brighter even than the MkI version described above. Runtime is however quite short - around 12-15 hours. That's longer than the Knightlite though ...
The LEDs can be any white LEDs, as they all seem to be equivalent electrically. Farnell are a good UK source of bright and cheap white LEDs. Maplins also stock white LEDs but these are not so bright and cost more - they still make a good light though.
(See Latest components)
Take a small silver front reflector - of the sort available from Halfords or any small bike shop that sells bubble-packed reflectors for kids bikes - and prise apart the prismatic front section from the black plastic backing. These are glued or heat-sealed together but a bit of persuasion with a penknife blade or, at worst, a hacksaw, usually springs them apart without much damage.
Drill four 4mm holes into the flat forward-facing part of the reflector, in a square, a diamond, or inline, as you prefer. And one hole in the black plastic backing. Like this but this is the MkI version which used 5 LEDs.
-led+ -led+ -ve +ve -led+ -led+
If weather sealing is not perfect, it’s a good idea with projects of this sort to decide which is to be the bottom, and drill or leave a small hole so that any water that gets in, can drain out again.
The whole thing hangs neatly on a P clip from the handlebars, or fits onto the fork crown mount that probably came with the reflector.
For the power supply, simply connect a PP3 battery (the small rectangular 9V type) to the twin lead. If you accidentally connect it the wrong way, the light won't come on - but it shouldn't come to any harm either. Incidentally the LEDs are over-volted using this circuit - but they seem to survive ...
It is just about possible, if you don't mind a squeeze, to build the whole project into a plastic 35mm film canister to make a self-contained front light. The best type of canisters are the black ones with grey lids (Kodak?) which have more space inside than most other types.
Final note - with this circuit arrangement it is also possible to experiment with other numbers of LEDs in any multiple of 2 - for example, a 6-LED light would simply consist of three pairs of LEDs wired + to -, all connected +++ to ---. Power with the same battery, but expect a shorter runtime!
Update - Latest Components
In the October '99 Farnell catalogue, two interesting White LEDs are listed -
301-5294 : 5mm : 1500mcd : 15 degrees : 3.6V : £1.18 993-864 : 5mm : 3000mcd : 20 degrees : 3.6V : £5.00as usual with LEDs, the newer versions offer increased brightness but also increased directionality, which is not ideal.
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