I'll throw out an open question. In fact, I'll throw out two:
Size and weight.
Handlebar real estate is a limited commodity, and they're not making more of it. Include a computer, a cue sheet holder and a bell, and the bars get crowded real fast. More so if they're 31.8mm. Several of the more common handlebar expanders won't take much weight. If you run a bar-mount, then it's critical. How large a light head are people comfortable with? Single-unit or separate electronics package? How heavy?
The BUMM indirect reflectors are 50mm at the front. INO's, Cateye's, and E6's (IIRC) are larger. They are the most controlled beams that I'm aware of. Any secondary (high-beam) emitters have to be parallel to that without being co-axial with it. That's a package with a 50x70 frontal area, minimum. Even with all the electronics in a separate package, that's getting big.
This connects to the "how much" question. If you want a total of 600+ Lm (raises hand), then you need to think about the combination of emitters that will give you what you want. Which relates directly to total volume and shape. Even if the 10mm optics for the XP-E turn out to be suitable, that's getting into a sizeable package.
If you're running three separate emitters side by side: two spot and one flood/elliptical, for instance, that's getting towards a 38mm diameter.
So what sort of dimensions are people comfortable with? For my own part, 40X100mm is about as large as I care to put on the bars. Anything larger interferes with cables and my knees. Anything smaller, and I can't fit Martin #10 into it. I asked my girlfriend, and she wants nothing larger than an L&M ARC head over the bar, or ~40X90mm underneath it. Weight is secondary, but it doesn't take much to overload the FSA or Minoura bar expanders.
I've read that piece by Peter White before. For a low-beam, he's got the right idea, and that's what he sells. For low to medium speeds, or trafficked roads, he's right. For higher speeds and more remote roads, I think he's flatly wrong. He has convinced a lot of people in the US that StVZO standards are appropriate for all circumstances. The patterns he's talking about are the "long narrow rectangle" that the BUMM and INO reflectors and the E6 throw. Great low-beam, no high-beam.
I don't buy the driver-irritation argument. Didn't then. Don't now. I'm perfectly willing to dip my light as a courteous road-user. I am completely unwilling to limit my available lighting because I might offend a driver.
As I've said, I know a lot of people using StVZO-compliant lights as sole-source lighting. For faster riding, or twisty roads, or both, the long narrow rectangle just isn't enough. If I'm descending at night, I want a high-output narrow spot, and I want it on the bars. At pass speeds, I need to be able to pick out the fog lines as far ahead as possible, and the tightly controlled beams won't do it. If I've got both, so much the better. If I'm on a pitch-black road in the *** end of nowhere in the middle of the night, I still want a long narrow throw. The better to pick up road signs in the distance, and critters on the verge.
Eamon
