More on lights

Posted on May 31st, 2010 in Opinion,pedal power by Julian Edgar

Regular readers will know that I like riding pedal-powered machines (conventional bikes, folding bikes and recumbent trikes) and that I very often ride at night.

Over the years I have developed my own high-powered LED head- and tail-lights, stories that have been covered in AutoSpeed. (For example, see the series starting here.)

However, in technology nothing stays the same and so about a year ago I started closely checking out the new wave of LED headlights designed primarily for mountain bike use. Living near Canberra, perhaps the Australian home of serious mountain bikers, I soon discovered shops selling LED lighting systems costing anywhere up to AUD$500. These typically used multiple 3W and 5W LEDs, lithium battery packs and trick circuitry to maintain light brightness and protect the batteries from full discharge. Different flash and power modes are also available.

In the shop these lights looked excellent, and attending a 24 hour mountain bike race showed how effective these top-line lights are in real-world conditions.

But, hell, $500…

So I decided to take a punt on eBay, buying a light that uses three Cree LEDs in a cast alloy housing, a lithium-ion battery pack and a dedicated charger. All for about AUD$100 delivered.

First impressions were very favourable, and I mounted the light permanently on my Brompton. Riding out into country south-central New South Wales, where the roads have no lighting and quite often there’s no moonlight as well, I found the light excellent in reach, spread and beam pattern. In fact, have the headlight aimed even fractionally high and on these country roads oncoming drivers kept flashing their headlights at me!

But then things started going downhill. Firstly, I was out at night, and a fair way from home, when the light extinguished itself. No warning, no reduction in power – just from full brilliance to off. Luckily I also run a light on my helmet so I could turn that on and get home. The problem? The battery voltage was low and when this happens, the light simply switches off. OK, so charge the battery up again and monitor how many hours of light are available – about 3 hours in fact.

But then a few weeks later I found the same problem occurred – great light then, bang, nothing. And the ‘run’ time was getting shorter and shorter.

On that occasion I found the AA cells in my helmet-mounted light were also getting low, and in addition to the darkness, there was fog. It was a dangerous ride home.

During this time I was running a rear Cateye red flasher, in fact a AUD$50 tail-light with six large, high intensity LEDs. It’s a good tail-light but it has a problem common to many: it’s quite directional and so if not mounted exactly right, visibility to car drivers falls off rapidly. Plus, despite having eight different flash modes, none was all that effective.

Mulling over all of this, I decided to dig out my previous home-made lights and rig up a new lighting system. I wanted:

  • Excellent front lighting – at least subjectively 75 per cent as good as the Cree x 3 system
  • Much better rear lighting, with more range and vastly better off-axis brightness
  • A great ‘run’ time
  • Some indication that the battery was getting low in charge
  • Little effort and no new cost outlay

So I dug out my front headlight, made from a stainless steel drinking cup, a 3W Luxeon LED and collimator, a heatsink and a 75mm magnifying glass. The tail-light I selected from my odds and ends box uses another stainless steel drinking cup, a lens salvaged from a camera, a red 1W Luxeon LED and another heatsink. (Both lights were covered in the previous series.)

I have a bunch of 12V Sealed Lead Acid batteries I’ve previously salvaged from discarded uninterruptible PC power supplies, and a home-made battery charger detailed here.

I added the Pulser  module and used simple ceramic resistors to regulate the LED currents.  I then added a diode and a handlebar-mounted switch so that I could easily operate the headlight in flashing or steady modes. The Pulser is set for a 3Hz flash rate with 12 per cent duty cycle.

It’s a relatively simple system that is also heavier than the professional approaches. But it’s also a system that has heaps of duration (something like 5 hours should be easily achieved, night after night if necessary), provides better overall safety than the previous system, and cost me nothing much to make. It also shows, by the very simple indicator of declining light output, when it needs to be recharged.

Kinda back to the future – something that on paper looks inferior but for me, works far better.

2 Responses to 'More on lights'

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  1. Bob Wilson said,

    on August 11th, 2010 at 6:53 pm

    I’m wondering if a pulsed power source whose duration is driven by the LiON state of charge could work. My thinking is pulsing the LEDs could effectively ‘dim’ them in proportion to the remaining charge. Say an LC circuit driven by a switcher?

  2. on October 23rd, 2010 at 6:50 pm

    Long time viewer / first time poster. Really enjoying reading the blog, keep up the good work. Will most definitely start posting more oftenin the near future.