Interesting concept. I like 15 because you see the 'source' of where the light comes from, but 17 and 14 look a little cleaner. What would it look like if the L and the E were shown complete? I think I would bump that 4 a little higher too. I visualize it like "lite to the 4th power" like you would see in math class. I definitely like the blue transition through the letters, it could even be emphasized more (even lighter to darker)
These are still an interesting entry, but I was hoping for a bit more cool graphic styling and fresh look when I entered the contest. I may have moved the 'simple bar too far to the left'