On 14 Mar 2005 07:03:32 -0800, wrote:

Sean wrote:
One other question while on the topic of replacing ballasts and
fluorescent
lights....
I am remodelling an empty unit to make a bookstore and they currently
have
about fifteen to twenty 8 foot double tube lights throughout the
store. (The
store is about 2500 square feet.)
I am considering replacing them all with about 50% more 4 foot units.
(So
about 22 - 30 units.)

Here, Britain, 8' tubes are mostly 125w, with some being 100w.
Presumably youve got 60w 8'. Basically the longer the tube, the better
the efficiency.

Yes, longer is more efficient, but only if all else is equal. Modern
4-foot T8 lamps are more efficient than just about any 8-foot T12
lamp. The only 8-foot T12 lamps that may come close require rare earth
phosphor coating which makes the lamp very expensive (due to its large
size and low sales volume) and only about 0.5 lm/W more efficient than
the comparable 4-foot T8 lamp (per data in the Philips catalog.) Plus,
this data is taken at 50/60Hz, so the OP will get a boost of 10% ( 9
lm/W) in the lamp efficacy alone by switching to T8 and electronic
ballast plus an additional boost of at least 10% from the more
efficient electronic ballast.

As Terry has pointed out, the cost of electricity to operate the lamps
over the life of the new fixtures is far higher than the cost of the
lamps and ballasts and fixtures.

--
Vic Roberts
http://www.RobertsResearchInc.com
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