How beneficial are cool tubes?

Hi, can anyone tell me how beneficial a cool tube would be please? As I had problems with heat the last time I was growing and my plant died.. The temperature was reaching as high as 38 degrees Celsius.. Approximately how low will a cool tubes temperature be, if my temperatures were 38 degrees with a normal open hood? I know it would all go by what extraction I am using but still can anyone tell me if it would be beneficial for me? Thanks

All the heat from the lights will be sucked out of the tent with exhaust. Very little heat left over. Im going to guesstimate that you will cool it by 75% or more

I use a cooltube for my 400w, ducted to a 6" 440CFM inline fan with a carbon filter. I have a variable speed switch for my fan so on cooler days, it doesn't need to be on full blast (and I turn it down at lights off).

The temp difference is tremendous, so long as you're expelling the air into a different room as to not compound the heat problems.

-spek

tottaly agree with what everyones saying, id recomend one of those 15 quid cool tube shades aswell, though you can be creative with others i used one from my old cfl 250w, a friend used a barn style one they all undo and bolt on so can be interchanged,

Ok thanks to all of your answers.. I have now bought a cool tube, only cost me £23 so all good... I've got a cheap extractor fan http://www.ebay.co.uk/itm/Hydroponic-Grow-Room-Fan-Tent-Inline-Air-Extractor-for-Carbon-Filter-Duct-4-5-6-/201019108285?pt=UK_Baby_Baby_Feeding_Bottle_Warmers_Coolers_LE&var=&hash=item2ecdac2bbd will this be ok? Or will I need a more powerful extractor fan?

No you need something more powerful. That is just a simple little duct fan. You need an "inline" fan.. that duct fan probably only pushes maybe 100 cubic feet per minute of air. You want like 400cfm.. dono what the wattage is of your light or how big your grow space is but usually a 6" 440cfm filter/fan combo does the trick for personal grows/cooltube setups

When I run an exhaust pulling from my cool tube, it takes the temp down 6 degrees fahrenheit. That's a pretty good number for me, considering the space I'm working with!