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[Shop-talk] tube fluorescent wattage

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Subject: [Shop-talk] tube fluorescent wattage
From: "old dirtbeard" <>
Date: Sat, 28 Feb 2009 11:18:03 -0800
Hi shop talkers.

All that compact fluorescent and tube fluorescent discussion got me thinking
about the wattage consumed so I got the old Kill A Watt out and tested a two
tube 4' fixture with solid-state ballast and a one tube 4' fixture with a
magnetic ballast (all with 40 watt bulbs). At the time of the testing my line
voltage was 122 VAC.

Interesting results, I think. The old single tube magnetic fixture started off
with the normal flickering at about 22 watts and slowly crept up to 34 watts
consumption at full brilliance after about 30 seconds.

The twin tube solid state started off immediately at 68 and did not vary. The
fixtures consume about 85% as much wattage as the bulbs are rated. I actually
expected them to consume more than the bulbs were rated assuming some
inefficiency in the ballast, and I expected the old magnetic ballast to
consume more than the solid state one.

I always wondered what was happening power-wise when magnetic ballasts were
flickering upon startup -- they are using very little power until they warm up
and reach full-illumination.

I tested a couple compact 15 watt CFL reflector replacements for the R30
incandescent bulbs, too. They start off about 9 watts and then gradually creep
up to 13 watts after a few minutes.

Just because I had it out, I tested a half dozen old incandescent 130 volt R30
65 watt bulbs. They actually drew 57 watts which is less than the 122 line
voltage/130 VAC rating would have suggested (61 watts). They all were used so
they may draw more when new.

Just to see if my Kill A Watt was reading low, I tested a new 75 watt
incandescent, and it showed 77 watts, so I think it probably is close.


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