Originally Posted by
Jaywalk3r
The XM-L T6 is pretty common in low-end lights. That is not to say that no good lights have been produced with the T6, just that it's widely available in the low-end stuff.
The throw produced by a light is dependent on several things, but the single most important factor is surface brightness, i.e., luminous flux divided by emitter surface area. Given two emitters with different surface brightnesses the one with greater surface brightness has more throw potential, period.
It is true that the reflector or optic also plays a role in a light's throw, given a reflector of the same depth and diameter, the light with the emitter with the highest surface brightness throws best. With bike lights, it's desirable to keep the light bezel fairly small. It helps keep the extra air resistance down and save cockpit space. Therefore, emitters with high surface brightness should be preferred when throw is desired.
The XM-L use a pretty large die, 5mm x 5mm, an area of 25 sq mm. Because it is so large, it is very difficult to focus in a reflector. At any time, most of the light is out of focus. An XR-E, by comparison, is 0.9mm x 0.9mm, for an area of about 0.81 sq mm. Although still not a point source light, the small area allows the light to be more easily focused.
The die of the XM-L has an area over thirty times larger than the die of the XR-E, but the XM-L is not 30 times brighter. That tells us that, for a given amount of space on your bar or helmet, an XR-E based light is almost certainly going to throw better than an XM-L based light. Experience with both emitters has shown me that, in the same sized reflectors, it isn't even a close contest; the XR-E throws light much farther.
Where the rubber hits the road or, rather, where the light hits the pavement, you are splitting hairs. Light is a pretty easy thing to observe. The inexpensive light...and we keep forgetting what the original discussion was about...made with the Cree XM-L T6 gets the job done quite adequately. You might be able to spend a whole lot more for a light and get a little improvement but, honestly, I don't that 1 out of 100 people could tell the difference. And once you start monkeying with the optics, all bets are off if you did a blind test.
My point is that you can spend $200 per lamp and use one lamp, maybe 2 if you are feeling particularly wealthy or you could spend the same $200 and get 8 or 9 of the less expensive light. Three of them puts out a stupid amount of light. And, as the technology changes, it's easier to jettison a $25 light then it is to jettison a $200 light.
Originally Posted by
Jaywalk3r
Given light A and light B, just because light A has more light going out the front compared to light B does not automatically imply that there is more light being reflected back to user A than to user B. There are too many other important factors to consider. The quality, not just the quantity, of the light matters.
Many people keep seeking out higher and higher intensity lights because they simply don't understand that the reason their current lights don't work as well as they would like is not necessarily insufficient brightness.
Sorry but that just doesn't jibe with what light does. Sure there are differences in the intensity of certain wavelengths but you aren't going to be able to notice too much difference with the human eye. If light A puts out slightly more light at 494nm and light B puts out slightly more light at 496nm, your eye isn't going to be able to tell the difference. Even if light A puts out more light 450nm and light B puts out more light at 620nm, you'll see one a little more greenish and one as a little more red but if each is putting out the same number of lumens, you'd be hard pressed to say which is more or less intense. As you said, there are too many factors to consider.
Originally Posted by
Jaywalk3r
Okay. Make it 120 mph. The point is that there exists a speed at which low beams project insufficiently to provide enough time to react safely. Switching to high beams increases throw, which increases the time available to react.
And this applies to bicycling, how? Even at 40 mph...a speed that I can easily reach on my bike as I commute...I don't out run the lights that I use. I've used other, far dimmer, lights in the past and it didn't have any impact on my speed...I did the same speed on the same downhill 20 years ago. The amount of light for seeing the road is more than adequate from any of today's lamps, provided that the lamp output is over ~300 lumens. I certainly wouldn't do the same hill at 40 mph with something like the Planet Bike Flash.
Originally Posted by
Jaywalk3r
That's incorrect. Automobile headlights have different beam profiles between low and high beams. It isn't just increased brightness. The beam shape is different.
Sorry, I was misstated. The beam shape is different but most of the automobile lights still use the same reflector with a different element for high beams. They, effectively, increase the light output from the same unit.
Originally Posted by
Jaywalk3r
Only increasing brightness, which is all changing modes on most bike lights does, doesn't provide much benefit. Even doubling luminous flux is perceived by human eyes as only a very small increase in brightness.
That's exactly what most cars do as well. They don't have separate reflector, just a different element. As for perceiving the change in brightness, it is noticeable. I don't use the low power settings on my lights because I don't see the point but the difference in the amount of light from low to high power is definitely noticeable.
Originally Posted by
Jaywalk3r
I do like a head mounted light on the trials, but not on the street. On the street, I don't want to shine my light everywhere I look. I don't want to inadvertently blind other road users or pedestrians, or annoy people inside their homes. In particular, blinding other road users diminishes my safety. I generally don't need to see into corners on the street, as the terrain is far more predictable, and street lights are common. I carry a handheld light, easily accessible while pedaling, for use when I need to see something my headlight isn't illuminating. In this way I get the most important benefits of a head mounted light, but I can look where I want without projecting light in that direction.
To each his own. I prefer the helmet mount and, based on a few decades of observation and not a small amount of thought, I don't see any of the problems you perceive with helmet mounted lights. If anything, the ability to move the light makes it less likely to blind other road users because I can direct it away from them more easily than I can a bar mounted light.