LEDs are starting to get a bad rep in the auto and motorcycle industries for being too dim, unfortunately it's also an unfair rep. Most people buy CHEAP LEDs, which are quite dim. If you pony up a couple extra dollars for a high quality LED bulb assembly they should actually be brighter than a standard incandecent bulb, as well as last longer, and pull less power.
Another reason LEDs tend to appear dimmer is that an LED has a smaller light arc than a standard bulb, especially on the cheap ones. A standard bulb can project light in about a 160 degree arc. Cheap LEDs are limited to about 30 degrees usually. One of the more innovative new LED bulbs takes a standard bulb shape and puts a bunch of LEDs inside it in a circular pattern, thus projecting a much wider arc of light.
Anyway, I made the mistake of buying a cheap replacement taillight for my Monster and it worries me that I won't be seen because of how dim it is. The better bulb is on it's way soon hopefully. On the other hand I bought very high quality LED turn signals from Roger Watsen design and they are VERY bright.
One last comment, as far as I understand it having a lens over the LED does not help brightness. The lenses themselves do very little to diffuse the light. The reason for this is that the LEDs are only projecting light outward from the lens, not toward the mirrored surface at the back of the assembly, which would effectively diffuse the light.
My 2 cents...
-Jordan