Requires long single tube sections (few or no joins), highest quality tube.
Sunlight collected can easily be lost before getting to the room.  The light reflecting tube going from the roof to the room must have near perfect reflectivity, few if any joins and no elbows if possible. 
Every bend or join will result in less light in your room.
One 4 foot section of light tube gives a better final result than two 2 foot sections.  Elbows create significant loss of light.  If needed they should never be placed directly above the ceiling as this results in bright and dark spots.  Some manufacturers design their product with integral elbows which lose light and are at the very top and bottom.
 

Requires deep translucent interior dome with minimal attachments around it.
Sunlight can easily be lost or misdirected at the diffuser dome.

	Deep translucent diffusers illuminate the room evenly, including the ceiling, without any harshness or glare
	Flat ceiling fixtures form spotlights on the floor.
	Clear fixtures are harsh and uneven.
	Prismatic fixtures appear brighter (harshness) but actually deliver less light.
	Pebble finish diffusers work well as a substitute.
	Trim rings or other attachments block horizontal light transfer and reduce the blending of ceiling to dome.

Compare for yourself and don't be misled.