The efficient transmission of light from your skylight top to the diffuser in a room of your choice, makes a huge difference to the effectiveness of a skylight. Commonly used is a flexi duct that is very easy to install and is preferred by many skylight operators but has definite limitations.
The transmission of light is restricted by the concertina type sides of the shaft, the steel reinforcing also frequently breaks away from the reflective material leaving holes in the ducting or causing it to fall out.
We prefer to use super duct, it has straight sides rather than concertina styles ducts.
The straight sided silver ducting will allow light to reflect efficiently from top to bottom no matter what the length ensuring that you get maximum light into your house.