In article ,
NT writes:
On Dec 11, 6:12*pm, (Andrew Gabriel)
wrote:
Ballast efficiency is marked with an EEI (Energy Efficiency Index)
rating on the ballast.

With the information you've given, I can't tell how much of the 22W
is a misreading due to power factor, and how much is ballast losses.
It can't possibly all be ballast losses, because the ballast would
overheat. For a 58W tube and ballast, max ballast losses a
EEI=D 12W
EEI=C 12W
EEI=B2 9W
EEI=B1 6W

If you are interested, you could pop the cover off, and read what
the ballast EEI rating is. It's no longer legal to sell EEI=C or D
ballasts in the EU.

If you want a more efficient light, rewire the luminaire with an
electronic ballast. You can get one which will do twin tubes
(although both will go out when one dies), or separate ballasts
for each tube. Electronic ballasts are required to be more efficient
than even the EEI=B1 rating.
mind if that's pasted into the wiki?
http://wiki.diyfaq.org.uk/index.php?title=Fluorescent

Yes sure. This is all for magnetic ballasts.

For electronic ballasts, there's A3, A2, and A1, but it's more
complicated how they're used, and I haven't looked up the precise
details. I think A3 only allows a total of about 1W more than the
tube power rating, and A2 and A1 have total power consumptions
less than the tube rating. This works by underruning the tubes,
and relying on the HF operation being more efficient to get the
same light output as at 50Hz operation. Would need to look into
that some more before it's accurate enough for the wiki though.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]