Re: How much power registered at meter?


"Victor Roberts" <xxx@xxxxxxxxxxxxxxxxxxxxx> wrote in message
news:mo8a031e0jtvu7qonumbpmb2vja54bg56s@xxxxxxxxxx
On Thu, 22 Mar 2007 15:50:21 GMT, "JohnR66" <nospam@xxxxxxx>
wrote:

I have a 30watt "sping" type flourescent lamp. Current draw is .5 amp, or
60va (120 volts).

I understand that the electrical meter (rotating disk type) cannot read
reactive power, only real power drawn.
Reactive power it typically a voltage to current phase shift. The current
wave form from these CFLs is more of a high crest factor rather than a
phase
shift. I wonder how the meter responds to this type of waveform?

The meter will read the actual power, as Paul has said. It
will ignore the reactive power.

Let me slide in another question. I have a fixture using 5 60 watt lamps.
This light is on 14 hours per day. I think we're still at 10 cents a kw/hr
around these parts, so I pay $12.60 a month to run this light (using 30
days
to calculate a month). I want to install a two 4' T8 tube fixture. I
estimate total power drawn would be 70 watts (two 32 watt tubes + 6 watts
loss in the electronic ballast. This should drop me down to only $2.94.

Actually, most 32-watt electronic ballasts run the lamps at
30 watts or less since the lamps are more efficient at high
frequency. 30 watts at high frequency would give a ballast
factor of about 1.0 But, you can buy electronic ballasts
with a wide range of ballast factors, so your mileage may
vary either way.

You can also buy 28-watt "energy saver" 4-foot T8 lamps
designed to run on ballasts for 32-watt lamps, and at least
one company makes a 25-watt energy saver lamp. You will
need to check the specs for your ballast to see what the
ballast factor will be for each of these lamps.

5 880 lumin 60 watt lamps give me 4400 lumens, what is a good lamp to use
that gives 3000K color temp, good CRI and and similar lumens?

To give a good estimate we would need to know the fixture
efficiency of the old incandescent lamp fixture and the new
fluorescent lamp fixture, and something about the light
distributions of each and the application. In the absence
of that data, we can proceeded with a comparison of lamps,
but you should understand this is only part of the story.

Normal 32-watt T8 lamps are rated for ~ 2850 lumens, but
there are also so-called Super T8 lamps that have ratings of
~ 3100 lumens. Two of either of these lamps would give far
more raw lamp lumens than the five 60-watt lamps you are
replacing. The 28-watt T8 lamps I found today all seem to
be rated for about 2750 lumens, so I'm assuming they use the
same technology as the 32-watt Super T8 lamps.

By using a ballast with a low ballast factor you can reduce
the power and light output further, assuming, of course,
that you don't want the additional light.

You have not told us if this fixture is being used in a
color critical application. If so, I would recommend a CRI
of no less than 82 and preferable 85, or even 90, if you can
find these in the CCT you like.

My own CCT preference for residential applications is 2700K,
but "best" CCT varies with light level and application and I
also know that personal CCT preferences are all over the
map. You're likely to get recommendations here ranging from
2700K to over 6000k.


--
Vic Roberts
http://www.RobertsResearchInc.com
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Thanks to you an Paul for sharing your knowledge!

75% or more of my house is CFL. Outside lighting is 100% CFL. I'm glad the
meter is registering only the real power used.

The fixture in question is a ceiling fan with 5 bulbs. 4 are open in white
tulip glass diffusers, so most of the light gets out. The center bulb is in
a white globe. Total efficiency is not known but I see there is some loss.

I was looking at a two tube F40T12 fixture with a wrap around diffuser made
of clear acrylic with the diamond pattern. I saw some GE tubes rated 3400
lumens, CRI 70 and color temp of 3000K (I think it was). Fixture was a
Lithonia lighting. No info on its ballast. CRI is not critical, but 75 or
better would be ideal. I wish this info was clearly labeled on all brands.

I'm going check around on some 32 watt T8s fixtures today to see if I can
find something with an efficient diffuser. Some of the more decorative
fixtures seem poor in this regard.

Thanks, John


.

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