The major advantage of LEDs is that you can distribute the light over the whole footprint of the tank. This prevents the light intensity from being too high near the top of the tank, while it is barely enough at the bottom of the tank. When you try to make a tubular "bulb" using LEDs you give up that advantage. Also, by using a lot of lower power LEDs, instead of a few high power ones, you don't need an expensive, heavy heat sink. Ordinary aluminum extrusions, such as channels, will work fine. Reef tanks may have differing requirements, but for planted tanks, this is my opinion.