self contained bike 'running' light ideas...

Hi Folks,

I've got a question or two about a project I have in mind that revisits the 'running light' thread that we all tossed around a few years ago. I've asked this over at MTBR without much response. Maybe it's a bit too elementary or nerdish...

I've ordered some Mobydrv boards and now I'm day dreaming about how easy it might be to build bomb-proof, removable, rechargeable and super-bright 'running' or 'be seen' bike lights based on a small Hammond (or similar) case, the standard CatEye 'flex' bracket and a large and very effective light diffuser I've found at GearBest (or maybe just half deodorant balls!)

I'm tossing around LED alternatives. The Mobydrv will deliver 1.4A and I could easily use parallel white and red triple boards, powered either by 1xLi or 4xNiMh (I like the idea of just using Eneloops).

However I've been reading about the Orfos bike lights and noted that both front and rear use 9 x 1/2 watt LEDs. I don't think I've ever even seen these. I've looked up a few references. Some indicate that 0.5W LEDs are built in the same form 'TIR' as the traditional 'lensed' 5mm LEDs (maybe a bit bigger) while others depict them as having flatter form-factors like MPCBs without encapsulation or lenses.

I'm thinking they may offer some advantages over powerLEDs:
- less worries about heatsinking
- the possibility of using multiples (in parallel) to get a larger array or larger 'apparent source size' with less need for a diffuser.

So I'm wondering if others have messed about with multiple half-watt LEDs as alternatives to single (or small groups of) powerLEDs? Any advantages? What configurations have proved useful? If the 9 LEDs in the Orfos lights are in parallel, I presume they'd soak up 4.5A. I don't know what driver is used but this does seem like a lot of heat to get rid of in a fully encapsulated design...

thanks.

Savvas.

Hmmm.... I've been thinking about a "be seen" light too, although I was thinking more about a small size. It's fun to contemplate what features you want, regardless.

I tend to agree that there is probably an advantage to generating light from a large surface area instead of a small area. The intensity would be lower, causing it to be less annoying to the viewer. A secondary factor is that the lower intensity would let the viewer see that there is a bicycle behind the light, instead of the more common scenario where the viewer has no idea what is behind that really bright light.

I think that your proposal to use a number of emitters is good. I'm not fond of the use of diffusers, mostly because they throw light in all directions instead of just the directions where cars will be. There are TIR optics that produce an oval pattern, so the light can be kept mostly at the level where cars will see it.

I would suggest that what is important (in terms of lowering the intensity and emitting over a larger surface) is not the number of the emitters, but the surface area (or emitting area?) of the optics. i.e. using 5 emitters that are each coupled with optics that emit over a surface of 100 square mm would be the same as a single emitter coupled with an optic that emits over a surface of 500 square mm.

In regards to heatsinking.... all LEDs need a decent thermal path to get the heat out, even 5mm LEDs. Using a number of smaller LEDs doesn't change the need to provide proper heatsinking.

In regards to power... for a "be seen" light where you intend the light to be aimed at other road users, I'd be surprised if more than a watt or two was really needed. This assumes the use of optics to control where the light goes, of course. My personal experience is that lights under a watt are quite noticeable, and lights running at 3 watts are rather annoying (especially when they flash at 5Hz or so, which seems to be designed specifically to induce a seizure!).

A flashing light will use less power on average, and I was toying with the idea of a light that ramps the light output up and down in a linear or sinusoidal fashion at a 1Hz or 0.5Hz rate. This should still be noticeable without being annoying.

Back to the matter of power.. you mention using 4 NiMH cells, presumably AA's. If you run the light at 3 watts, that'll give you about a 2 hour run time. A strobe mode will increase the run time. For heatsinking, I built a light powered by 4 AA NiMH cells, with aluminum making up roughly 60% of the housing surface. It's more than adequate to get rid of 3 watts of heat.

Hi Steve,

Thanks very much for your excellent (as always) observations. I don't have your technical expertise for circuit experimentation so I have ordered a Mobydrv driver board from DrJones (on the mtbr forum). He uses a commonly available programmable board capable of providing a 'pulsed' flashing rather than on-off - what I think you may be referring to as ramping light output up and down in a linear manner. This also appeals to me more than a flickering on-off pattern for urban riding.

He's going to provide me with a board that provides 2 x 700ma channels. I'll use one for the front running lights and the other for the rear so that I can accommodate two different Vfs. For the first iteration I'll probably use 3 separate red XP-Es at the rear, each with their own optics, and 3 white LEDs at the front arranged in a similar manner. This because there are some innovative 'beacon' optics I'd like to try out for the 2 x lateral LEDs along with a more conventional central focussed beam optic for the central one. I will eventually try out an array of 0.5w LEDs as well, but for now I have quite a specific application in mind for the separate powerLED arrangement.

I've been largely inspired to tackle this by past creations outlined on cpf from Mr '1 what' and others (shame all the pics seem to have disappeared from that thread). I have an old Pashley Moulton APB which has wide, flat racks front and rear. This is my main commuting bike and has seen a great deal of experimentation over the years (including various unresolved attempts at electric drive). It runs a dynamo for the main headlight so the running lights I have in mind only have to perform a 'be seen' function day and night. The leading and trailing edges of the low-placed platform racks are both curved and so lights placed just underneath them lend themselves to a 'be seen' arrangement and physically protected from the usual knocks and scrapes to which lights are vulnerable when mounted on the side of forks etc. I envisage mounting the LEDs on 2 narrow alu plates arranged across the central axis of the bike with the ends bent at a slight angle - maybe about 10-15 degrees - to broaden the visibility angles of the side lights. All theoretical of course at this stage!

I know that it's become conventional to use Lithium batteries these days but I feel there are real advantages in using NiMh AAs or similar. There's less anxiety about battery protection of course and because I've accumulated a box of 8-10 Eneloops I can easily keep a set on charge all of the time. Thanks for your calculations with regard to run times - not something I've managed to do myself yet.

I've ordered the driver and hopefully will see it in a couple of weeks. I've got suitable LEDs already - red XP-Es and white XR-Es - and I think I can scrape together sufficient optics from my parts box from past experiments. I do have to find a suitable battery box as I really want something that is weatherproof. Maybe something salvaged from a cheap Chinese headlamp... some research needed I think!

Thanks again for your ideas - much appreciated. I'll keep the board posted.

Savvas.

I've had a B&M tail light with an optic like the Ledil that you link to... the B&M just used a little 5mm LED, and was rather pathetic. If it was used with a 1 watt LED, I think it might be very nice indeed!

OTOH, I'm still fond of the idea of using a large array of small LEDs, or a few LEDs with rather large optics. Really, this is the same approach as what most cars use. I've been using the same hacked up taillight on my upright commuting bike for about ... 15 years or so. Good heavens! It's time to put together something proper that doesn't look like it was thrown together as an afterthought.

Regarding NiMH cells.. I've stuck with those too, largely out of habit. I suppose it would be safe to use protected 18650 cells or something similar. I should peruse the "batteries included..." subforum.