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T-8 lamps in T-12 fixtures, and ballast types

"Shiao Y. Wang" asked:

Would the bi-pin lamp holders for T-12 bulbs hold T-8 bulbs? I'm
thinking about switching from T-12 to T-8 lamps in my existing
shoplight-based hood. If the lamp holders work for T-8 bulbs, I should
be able to switch by simply replacing the ballasts with electronic
ballasts. Am I correct? Thanks for any advise.

 - --
You are absolutely correct.  I'm assuming you have the original lamp holders 
in your fixture, not the aquarium water resistant cap type, which are sized 
according to the tube diameter.  Your fixture will work with T-8 lamps (4', 
32W, not to be confused with the 1" diameter, 40W aquarium lamps) after you 
replace the ballast with one designed specifically for 32W T-8 lamps(there 
also are electronic ballasts designed for standard 40W lamps, e.g. the 
Coralife ballast).

Assuming that most of the time you leave your lights on for 10-12 hrs. at a 
time, you may want to consider an instant start ballast rather than rapid 
start.  Instant start ballasts use slightly less electricity to run lamps 
because they don't maintain a current through the cathodes at the end of the 
tube(the cathode is the filament inside each end of the tube, the ends of 
which are connected to the pins).  Rapid start ballasts always maintain a 
small current through the cathodes, wasting a small amount of energy.  The 
reason rapid start ballast are sometimes selected is that they have a 
smaller effect on lamp life for each on/off cycle.  Instant start ballasts 
start the lamps by sending a high voltage across the tube, which is more 
stressful on the cathodes than the gentle heating they would receive from a 
rapid start ballast.  This reduced life is obviously not a good thing 
either, except that since you're leaving the lamp on for quite a while each 
time you turn it on, the effect of the high starting voltage on the lamp 
life is reduced, relative to the operating hours' effect on lamp life. 
 Furthermore, if you're in the habit of replacing your tubes when they're 
less than a year old, this really doesn't matter.  I don't replace my tubes 
every year, and the set in my hood that are being driven by an instant start 
electronic ballast are 2 years old.

Wade Shimoda
Honolulu, HI