My roofer has just installed three Velux sun tunnels. One will have a rigid tube, once the parts are delivered (it was broken in the box). The other two are flexible and I have pulled the tubing as taut as possible and find the amount of light, even with the sun out, to be very negligible. They are certainly not worth the cost of installation and product. I bought Velux as I am happy with their roof windows and did not research other than their website, where the difference in amount of light between rigid and flexible is not quantified. I have since found the amount of light can range from 3x to 10x more with rigid tubes. My question: can I switch out the flexible tubes for rigid and does Velux make elbows that allow for between 90 and 120 degree turns, as does Solatube?