quoting:
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.)


I am considering doing this mostly due to the high price of 8' tubes and
ballasts. (In this part of Canada the 4' tubes go for about $1.40, while the
8' go for about $6-$7). Also the ballasts for the 8' bulbs costs about $30,
whereas I can get a whole 4' unit for about that price. ($20 for a cheaper
one that will probably break down in a few years, $30 - $35 for one that
will hopefully last.)

$1.40 - is this for 34w, 40W, or T8 tubes? The local GESupply sells 34w CW
tubes for about $1.30 currently, and about $2.50 for T8. 40W tubes are
currently about $2.25 .

8' for $6 to $7 - Is this for 60W or 75W tubes?



So there are actually two questions:
1) Will I retain a similar amount of light from replacing those units? (I
know that their will be a small drop in light, but I just wanted to know how
noticeable it would be? Or should I just double the number of 8' units and
achieve near the same amount of light?)


Things to consider:

It all depends on 60W vs 75W tubes in the 8' lights now, vs T8 or 34W or 40W
in the new lights.

Generally, old and most new magnetic 8' ballasts light 75w tubes to nearly
full rated output. Same with old and most new magnetic ballasts for 4' 40w
tubes.

34w tubes start out about 15 percent lower at full rated output, but they
always never light more than 94 percent of their rated output on any ballast,
even if that ballast was previously lighting a 40W tube at nearly full
output. The same goes for 8' 60W vs 75W tubes on same ballast.

Typical T8 ballasts light T8 lamps to 88-92 percent of their rated output.
You generally have to seek out ballasts that light T8 lamps to something near
or over 100 percent of their rated output.


2) Is it going to be cost effective over 10 -15 years to replace all these
units? (Or am I wasting a lot of money trying to avoid spending $6 - $7 on
the 8' tubes and $30 on a few new ballasts to replace the 3 or 4 that are
burnt out?)
Thanks for reading this long post, and for any answers or suggestions.
Sean.


Generally, yes if you go with T8. (even better if you get ballasts that light
the tubes to nearly or above their rated output.) If you ever consider
saving energy with those 34W or 60W tubes - skip them. Go straight to T8.
If you do decide to stay T12, just stay with 40W or 75W tubes. Don't use
those 34w or 60W tubes, they are rather poor.


BTW, did you read my post about fixing your fish tank light?