Jaywalk3r

To which MagicShine are you referring? The early ones I remember utilized SSC P7 emitters, which provides a pretty wide beam, without much throw, not very suitable for fast riding.

Cree makes many different models of LEDs. Saying that Crees have a tight narrow beam is like saying Continental tires are super-skinny. Some are, many others aren't. Many different Cree models are used in portable lighting applications, including flashlights and bike lights, including XR-E, MC-E, XP-G, XP-E, XM-L, XP-G2, XP-E2, and XM-L2. Sitting in reflectors of the same diameter and depth, they will all have different beam characteristics. The XR-E, XP-E, and XP-E2 all provide tight, narrow beams. The XP-G2 is a bit wider, with the original XP-G wider still, though neither could be considered floody. The XM-L and the XM-L2 are both very efficient and can be driven pretty hard, so they throw okay by virtue of putting out tons of light, some of which is in the hotspot, but they certainly aren't tight narrow beams. Most cheap, bright lights being sold these days utilize the XM-L emitter. The MC-E puts out a ton of light, but it is a very wide beam, with very little throw.

Not only is the emitter model important, but also the efficiency bin and the tint bin of the emitter matters. During the manufacturing process, emitters of the same model are separated based on how bright they are at a particular voltage and current with a nearly ideal heat sink. Cree identifies these bins with a letter and digit, like Q3, Q4, Q5, R2, R3, R4, T6, U2, U3, etc. The higher the letter, the brighter, therefore more efficient, the emitter is. Within the same letter, the higher the number, the brighter the LED is.

It gets more complicated, still. Each emitter is also binned according to chromaticity. This provides information about the emitter's correlated color temperature and similarity to an ideal black body radiator of the same temperature. For some emitters, the color rendering index value is also specified, which tends be related to the chromaticity.

Most cheap LED lights use emitters from not very high efficiency bins, high CCT (i.e., angry blue cool white tint), and a low CRI value. In other words, the quality of the light produced is very poor. They are fine for "be seen" lights, but not very well suited for "to see" lights. Why is this?

How much light comes out the front of your light isn't what matters. What matters is how much light is reflected back to you by the objects you are illuminating. LEDs produce a very uneven distribution of component colors that mix to make white light. Some are worse than others. While they are technically broad spectrum emitters, there are lots of peaks and valleys if we graph their output by luminous flux versus wavelength. It isn't smooth like, for example, a good incandescent emitter. Consequently, different colors are illuminated at different levels.

Cool white LEDs, for example, provide an overabundance of blues, but not much in the way of yellows or reds. So, if riding in an area with lots of blue objects, those blue objects will be surprisingly well illuminated for the amount of light being emitted from the LED. On the other hand, in an environment with lots of yellows and reds, there won't be a lot of light reflected back at the user relative to the amount of light that coming out of the front of the light. Objects reflect only specific wavelengths of light. If the LED produces those wavelengths in low quantities, then there will only be a low quantity of light reflected back at the user. The rest of the light is absorbed by objects as heat, so is wasted.

Natural outdoor environments tend to have an abundance of warm colored objects, so cool white LEDs are at a severe handicap in such environments. While cool white LEDs tend to be slightly more efficient than neutral and warm white LEDs of the same model, that doesn't mean that users will be able to see more with them.

Neutral white LEDS tend to be a little better, with a more even distribution of component colors. Warm white LEDs tend to be better still. Best are high CRI emitters (CRI of 90+). High CRI Cree emitters tend to be warm, about 3000K. (Nichia offers a well regarded high CRI emitter in neutral white.) The price of such emitters tends to be much higher than the cool white, low CRI versions, so they usually aren't found in cheap lights. They are, however, well worth the extra coin, in my experience.

I actually said different riding speeds and environments (not necessarily different bikes) require different lights for optimal lighting, and that assertion is correct. An easy thought experiment illustrates the point nicely.

If a motorist is driving 20 mph, are his high beams necessary? Of course not. He's not going fast enough to need to see that far ahead. His low beams are perfectly adequate. What if he's driving at 80 mph (or faster)? Are the low beams still adequate? Of course not. At those speeds, he will easily "outrun" his headlights.

One might point out that, while not absolutely necessary, the motorist could use his high beams at low speeds as well as high speeds, one beam shape for both. If we disregard light pollution and courtesy to other drivers, that's a fair point. Except that the car produces its own electricity to power the lights (much like a bike with a dynamo hub). For battery powered lights the rider must purchase and carry the power supply for the lights. Shining light in places it isn't needed is inefficient and suboptimal. That includes shining light farther ahead than necessary for safe riding at typical speeds.

So, while one can certainly make one light work for multiple riding speeds and environments, it isn't optimal.

I would disagree. Off road, I don't want a cutoff beam, which is preferable on the road (Disclaimer: my current commuting light simulates a cutoff beam passably well, but doesn't actually cut the beam off.) Off road, I want a supplemental light on my head, which I absolutely do not want on most roads. My speeds on road are higher, so I need to be able to see farther ahead than when off road. Off road, I'm more concerned (compered to urban street riding) about critters intercepting me along my path, so I prefer a much wider beam than I need on road.