ALL regular glass greatly diminishes the flow of UV-B rays.

Special glass is needed that allows these rays to penetrate thru.

Cool tubes are nothing but glass tubes that channel the air across the bulb, thus removing the heat thru vacuum.

If you study the failure of the $151,000,000 BioSphere project, you will find the failures was due to massive overgrowth of soil bacteria...which were allowed to grow un-checked because they built the place with glass panes.

These panes eliminated most all UV-B rays.

UV-B damages plant cells and these plants we discuss here respond to that damage by producing additional resins. So, unless you have a special glass tube, these cool tubes block UV-B rays.

While it will not hurt your harvest, the use of them will prevent your plants from being as potent as they could be.
HARDDON Reviewed by HARDDON on . Is my light TOO powerful?? So i have a small, 2' x 2' grow space. But i have the opritunity to get a 400 W HPS cheap (for flowering). obviously it would have to be hung about a foot above the plants....it has a cool tube. Will it be more trouble then its worth? should i just go for a 250. Does anybody have experience using a big light in small area? Rating: 5