Wednesday, October 6, 2010

Techie Tuesday - Cyclists Lighting System

Learning to fly in Los Angeles at night, if nothing else, is an education in lighting. Once off the ground, and out of the TCA, the familiar disappears into an endless carpet of lights with some random dark spots - defined only by the hard dark line of the ocean. Lighting on aircraft is well-specified by the FAA, so you'd think it would be easy to spot aircraft, but it's anything but easy.

Most commercial airlines now require you to raise the window shades when landing so the cabin windows are lit. They have almost universally taken to brightly lighting the tail of the airplane too. (which G.I.T. requirements would this satisfy?)

Ghosts of lighting past (photo courtesy of Javier Arroyo)
When I took up riding bicycles seriously a few years ago, and this time of year rolled around, I got to thinking of all the lessons I learned about lighting moving objects for identification and collision avoidance. It turns out, many of those lessons apply.

This system is focused on helping others see and react to you. It doesn't cover your being able to see the road, but of course, that is not only important, but a legal requirement too. Without further adieu then, I'll present my recommended lighting scheme.

The G.I.T.  LIT lighting system 
- Grab
- Identify
- Track

The highest priority in lighting is to GRAB someone's attention. Until then, they're incapable of responding or reacting, because they're unaware there is anything around that requires it. Strobes and flashing lights are excellent for this task. Both allow a light source to be much brighter than if constantly on, so be sure to buy a bright light. In any case, the battery drain will be dramatically reduced for flashing or strobing lights, so go big, and as they say, "take two, they're small".

Noticing flashing lights is much, much easier - relying on the very primitive part of our visual system that senses motion (remember Jurassic Park?), and there's evidence they appear brighter than constant-on lights. 

The next highest priority is making sure you're easy to IDENTIFY. Every object has unique properties and behaviors. Motorists rely heavily on knowledge of what they're looking at in order to react appropriately. A jogger, cyclist, and motorcyclist all share some characteristics, and differ dramatically in others.

A jogger you might expect to be facing you, and if lit, to have the light bobbing up and down. Their feet would also be moving in a much different way than the circular motion of a cyclist. A cyclist may be facing you, or may not, but they will be going 3-5 times as fast, so reaction times are compressed. Wheel reflectors will also be making their characteristic roundy-round motion. You wouldn't expect a motorcycle to be facing you, or make quick or radical moves like a jogger or some cyclists.

You would expect a motorcycle to have a powerful lighting system, more powerful than a bicycle and much more powerful than a jogger. It will also be going faster, and can be expected to accelerate faster. If you think about it, even if something grabs your attention, you don't really know how to react until you know what it is.

Anything that lights you and your bicycle well enough so it can clearly be seen as a whole at some distance is best. A headlight mounted on the back of your bike that shines on your backside is excellent. No guessing required. Failing that, highlighting some behavior that only a bicycle can exhibit is good.

Those spoke-mounted reflectors we all remove 10 minutes after we get the bike home, and legally required pedal reflectors - which no clip-in pedal I have ever seen has - are both excellent, but who uses those? I don't (my Sidi shoes do have a quality reflective patch on the heel though).

Helmet light from a donor BRT legstrap
Clothing with reflective piping that creates a distinctive silhouette is very good, as are helmets with silhouette reflective tape. Illuminite type jackets and vests are very good as well.

I have Velcro-ed a Planet Bike BRT strap's internal optic fiber ribbon onto the back of my helmet. It curves around behind the back of the helmet, and is visible from the front, back, and both sides. It's at a motorist's eye level, and when I turn my head to clear a turn it cues motorists where I am looking.

A better variation on this would be optic fibers arranged like the plumage of a Roman helmet, but I have not been able to find one. A unique symbol, similar to the very successful slow moving vehicle triangle is certainly begging to be introduced, but to date, has not been.


Once motorists notice you, and figure out you're a cyclist, they need to be able to TRACK you, or more likely, your lights, to determine course, speed, and proximity. Tracking requires constant on, non-flashing/blinking/strobing lights, and powerful ones. These are primarily rear-facing red lights mounted on your frame or seatbag, but could also be helmet mounted. (assumes you already are using a good headlight, which shows you the road, and allows others to track you when head-on)

Strobing or flashing lights are incredibly difficult to track at night, and since tracking requires constant visual acquisition, it's very demanding of the motorist's time and attention, and perceptually appears dimmer, so this light must be very bright. At long distances, it is likely that you will not yet have been identified when tracking begins. It is by tracking your speed though that the motorist will first begin to form an opinion as to what you are - once you've grabbed their attention. 

While your tracking light will rarely be able to identify you, it can, and sometimes does, grab, the motorists attention. It just isn't very efficient at grabbing it, since flashing lights don't consume nearly as much power, produce as much heat, and for any given power source and bulb, can therefore can be pushed much harder to produce more light. Trade them off.

Have two lights that provide fail-over for each other in either role, as you are trusting life and limb to a battery or few, and a few cents worth of plastics and electronics. This also effectively doubles the battery life of the tracking light. Bringing spare batteries is also an excellent idea for these power-hungry lights, which I always mean to do.

If forced to chose, favor a strong flashing light paired with a dimmer constant light. It's possible to track a strobing light IF it is paired with a still-visible constant light source. Aircraft strobes were designed for years to dim, but never completely turn off for this reason. IIRC, the standard was a repeating pattern of 100-20-100% intensity.

Better to not be forced to compromise, but sometimes fate intervenes. Unfortunately, in LA there is so much ambient light you still lose aircraft between strobes, but not so in rural areas. It's very important that the dim part of a strobe-cycle be bright enough to stand out above the ambient light level. (again, strobes aren't 0% and 100% but 20% and 100%)

Of these three requirements, the IDENTIFY one is the hardest to satisfy. You can be glowing like a Christmas tree, but if the guy can't tell what you are, you still run a pretty high risk of an accident. One promising development here are tires that have reflective sidewalls. From the side, this would make your identification instant and trivial. Worth looking into this winter.

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1 comment:

Gotta Run..Gotta Ride said...

Even with the best lighting etc riding in a group also make things safer! Still, riding with a group at night can be tricky if they are not well experienced.

I will be spending a good amount of time on my trainer in the garage this winter I fear :)

Great blog post.