Steve K Provides Some Enlightenment

In my recent whine about current (no pun intended) LED headlights, I released an unabashed troll attempting to lure friend, bike dude, and soldering-iron gunslinger Steve K to talk about lights. Being a swell fella, he's obliged with perhaps one of the more concise and readable cut-through-the-marketing explanations descriptions of how lights are measured and how those measurements translate into reality. Since I'm learning (slowly) that this blog improves when I shut up, I'll let Steve talk. Take it away, Steve!

The biggest confusion is just about the way light is measured... most often in lumens, but sometimes in lux, and sometimes the manufacturer just says "it's a 3-watt LED!!!" Well, there are 3-watt LEDs and then there are 3-watt LEDs!

The quick explanation is that lumens are a measurement of the total flow of photons out of the light. Sort of like saying that a pump can output 2 gallons an hour.

By contrast, lux is a measure of the intensity of light hitting the target. To quote the Wiki folks: "It is used in photometry as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface."

The thing that converts the lumens to lux, so to speak, is the optics or reflector of the light. If your light's reflector (or lens/optic) is designed for mountain biking, it'll produce a wide beam and scatter the precious photons over a large area. As a result, the light at any given spot will be dimmer (i.e. a lower intensity) than what you would get with a road bike headlight that had a tight beam that spreads the light over a relatively small area. Same number of photons hitting the ground, but producing a higher intensity since they aren't being spread as thin. Simple, eh?  Same number of lumens in each case, but the lux will be lower for the wide beam relative to the narrow beam.

The business about wattage is confusing because it is usually a measure of electrical power, not light power. Most modern LEDs will produce about 100 lumens per watt, so a nice Cree XP-G being run at 3 watts will produce about 300 lumens, and can make a decent road headlight. A cheap LED might only produce 70 lumens per watt, which will be barely noticeable as being dimmer than the Cree XP-G. Human vision is logarithmic, so a big change in lumens really doesn't look like a big change to us.

So there you have it. The introductory lecture in our Lights 101 course. Please address your questions to Professor Steve in the comments section. And big ol' thanks to the professor for contributing his astute guest lecture.

More Folding Bike Fun: A Reader Responds

Reader Alex P. (everyone: "Hi, Alex P!") recently contacted The Cycle World Headquarters in response to the folding bike "dorkaleur" (trademark pending) cooked up in our top secret Skunk Works laboratory. Seems our crack team is standing on the shoulders of giants yet again, albeit ones riding on very small wheels:

 Images courtesy of Alex, so please do not hork them.

Rather than jabber on when I know next to nothing about the bike in question (like that's ever stopped me), I'll let Alex tell his own tale:

I built the frame. It's heavily inspired by the Raleigh Twenty, except for front geometry and hinge placement. The front geometry copies the Swift Folder. A couple years ago I took a position at work where I would be traveling a lot. I had built a full size frame the previous year and decided to try making a folding frame before the travel started. For a little over a year I often traveled with that bike (set up as a fixed gear with a front drum brake) packed in a soft bag (this is the bag directly over the rear wheel). I'd get out of the airport or off a train, unpack the bike, roll up the soft bag, tie my backpack up front and cycle away. It's a fine way to travel, although I will say the bike got pretty beat up on a couple flights.

The photos are from a two week tour of Shikoku Japan. I felt I could travel indefinitely with that setup, thanks to the massive cargo capacity of the backpack. Well maybe not indefinitely. I was getting tired of not being able to coast.

Got the touring itch yet? I know I do.

HUGE thanks to Alex for letting me share his words and photos. With reader contributions like this, I'm starting to wonder why I don't outsource this thing more often. Definitely classes up the joint compared to the usual drivel.