yup no light comes in or out
thet can go pretty close to the cooltube, they can probably get within 10cm(4 in) witouth getting bleached.
Still i just got 75-80cm of growing height with 27cm pots, no tall sativas for me

In the future i'll try Scrog, wich probably is the best method for me due to the lack of height, but since this is my first grow with this setup (and second grow ever), i wanna test it out first