The Light Cannon is a bit whiter. My own Helios has a creamy white look to its beam. Mind you, it's definately NOT yellow, nor is it pea green, but a blushed shade of white, if you can imagine that. It's like Vanilla color; that's the closest I can describe it. My Sony FC-707 can't distinguish between color shades this descriptive, so I'm afraid a digishot of it just looks white instead of vanilla. The LC100 has a slightly orange tinge to the beam color in the dead middle, in a shape almost like a galactic swirl in the middle of the beam. It doesn't interfere much with light perspective, however. The LC100 is a bit of a spotlight, with a good wide hotspot and a white, smooth spill light; its spot is about a 10-15 degree spread. The Helios has an overflowing flood to its sides, quite well, in fact, that it's great to walk around outside with the flood, and yet it still has a wide spot area of bright light, probably around 20-25 degrees spread.
The Light Cannon throws farther than the Helios can. I'd say whereas the Helios can throw to about 25-30 yards away, and this is an actual "beam" to that distance, not just a reflective throw on some sign or reflector (meaning I can actually see the beam on an object, rather than only see some light reflection from a stop sign or a road reflector), the LC100 can throw a beam at least 50-75 yards away.
The LC100 is notoriously fragile. I'm not going to dispute this, or what Craig Johnson said in his review of the LC100, because my MaxaBeam is also prone to damage from minor drops (like 3ft-6ft from the ground). I wouldn't dare drop the LC100, and although it's made of tough ABS, I wouldn't try scratching it either. It's an awesome divelight, though, and if you baby it whenever you use it, it should do well.
The Helios is literally a Mag (<---okay, ditching the fad now) without the regular bulb, so you can imagine that it's quite durable. You'd be able to run it over with a car and it's fine. The LC100 probably won't like that. The Helios is much more durable than the LC100.
I put NiMHs in both. (8x C NiMHs in LC100, and 6x D NiMHs in the Helios)... The LC100 has a runtime of about 2.5-3 hours with alkalines. The Helios runs about 2 hours bright on alkalines. The LC100 goes blaring yellow and just about dies at the 5-6 hour time, but the Helios can go on for 15+ hours on trickle mode...
Hope that helps...