Is restrike a myth?
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Old 11-09-2007, 02:14 AM   #1
jbolinger
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Is restrike a myth?


Does anyone have a link to an Authoritative Source that says why this is a problem? I'm talking about compact fluorescents here.

I am an engineer by profession and, IMHO, have a very good understanding of 'How Things Work' and a good appreciation of the physics involved.

My 'How Things Work' says that a photon leaving the lamp and striking another part of of the lamp can do 1 of 3 things:
    1. Pass right on through and out the other side. No problem here.
    2. Be absorbed and reemitted at the same or different wavelength. This is also no problem---just contributes to the total spectrum.
    3. Be converted to heat, which should already be included in the efficiency of the lamp.
I would hazard a guess that some of all three occurs. So the only problem with restrike then is #3. Is this what everyone is worried about?

Jim
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Old 11-09-2007, 03:12 AM   #2
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I kind of agree with you.

I believe that there is a "restrike", but I do not think it is as major as most people say.

There are arguments for both sides. I personally just added some mylar above some spiral cfl's and I can notice a difference, although a small difference. I also just replaced 27 watt spiral cfl's in 3 clamp lights over my 20 gal with a coralife 65 watt and noticed a major difference.

I really think there are a lot of variables, but I would LOVE to observe the scientifc aspect of this. Let the debate begin!
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Old 11-09-2007, 03:21 AM   #3
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If you've ever seen the same bulb lit by itself, under a standard reflector and with a parabolic reflector such as those from AH Supply you'll notice a definite difference in light output.

Even if #3 is the only "issue" it's still a concern as far as efficiency goes.
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Old 11-09-2007, 03:23 AM   #4
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Don't forget the light bouncing off the surface/s as well.
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Old 11-09-2007, 03:28 AM   #5
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Would conversion to heat really be included in the efficiency of the lamp itself? I would have to agree with you that number 3 would be the issue, although I don't think this is why people get parabolic reflectors. Reflectors solve more than just the issue of restrike. Just because the light coming from the lamp is not being absorbed back into the lamp does not mean it is being directed at plants and being used.
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Old 11-09-2007, 03:32 AM   #6
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Are you saying that it should be included in the lamp's efficiency or efficacy? Luminous efficiency is the percentage of light that can be used (i.e. relevant wavelengths), where as efficacy is a measure lumens/watt. (Sorry, just did a presentation on LED lighting).

I don't think this should be included in the lamp's efficacy, because this light is lumens that were generated by the lamp (which is covered by the efficacy), but because it did not stay as light energy, became heat.
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Old 11-09-2007, 02:33 PM   #7
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Quote:
Originally Posted by fishscale View Post
Are you saying that it should be included in the lamp's efficiency or efficacy? Luminous efficiency is the percentage of light that can be used (i.e. relevant wavelengths), where as efficacy is a measure lumens/watt. (Sorry, just did a presentation on LED lighting).
Most of my expereince is with radio transmitters and antennas so I tend to think in those terms. By efficiency I mean the amount of light radiated compared to the power supplied to the lamp. For a radio/antenna the energy not radiated ends up as heat. The same thing would apply here, I think. I was not talking about the spectrum of the lamp. That is an entirely different question than restrike, isn't it?

Jim
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Old 11-09-2007, 02:42 PM   #8
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Quote:
Originally Posted by fishscale View Post
Reflectors solve more than just the issue of restrike. Just because the light coming from the lamp is not being absorbed back into the lamp does not mean it is being directed at plants and being used.
I fully agree. Making the light go where you want it is an entirely different question than 'restrike'. Just guessing, I would think that only 10-20% of the light would go into the tank (on a typical set up) if you do not use a reflector.

My question was meant to stimulate discussion of 'restrike'. By reading various forums I got the opinion that some people think that the energy 'restriking' the lamp is sucked into a black hole or something.

Jim
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Old 11-09-2007, 02:44 PM   #9
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Quote:
Originally Posted by mistergreen View Post
Don't forget the light bouncing off the surface/s as well.
Sorry. You're right. There should be a:

1a. The photon bounces off.


Jim
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Old 11-09-2007, 04:36 PM   #10
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I'm not a lighting engineer, but when I had to replace all the fixtures in one of my buildings, I spent quite a bit of time dealing with one. The choices were wide ranging and there was a huge difference in cost of the fixtures. The ones that were the most "efficient" (put the most useable light where you need it) had the lowest restrike ratings and therefore had lower operating temp & power consumption ratings. They were made by firms that had considerable engineering resources and were correspondingly more expensive. The fixtures I ended up using used the same bulbs and similar ballasts to the previous ones, but saved enough $$ to pay for themselves in less than a 2 year span. To me that dissolves any thought of restrike being a myth.

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Old 11-09-2007, 05:22 PM   #11
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Quote:
Originally Posted by LS6 Tommy View Post
The fixtures I ended up using used the same bulbs and similar ballasts to the previous ones, but saved enough $$ to pay for themselves in less than a 2 year span.
How do you know this to be true?
other than believing their marketing.

usually when you replace typical 2x2' or 2x4'
drop ceiling fixtures, restrike benefits do help
by delivering better light, but not that much
savings in electricity against replacement costs.

one of the myth's of drop ceiling fixture replacement
is a savings on HVAC. it's often true you only enjoy
that if they are air return fixtures, and you use the
drop ceiling as a return. if you have separate air
return ductwork, then the fixture's heat impact on
your HVAC costs are of little consequence.

always take a "lighting engineers" advice with a grain of salt,
since his training is paid for by the fixture makers themselves,
and his bias can often cost you a lot more than you need.
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Old 11-09-2007, 06:52 PM   #12
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I think that restrike is probably not accounted for in the lamp's efficacy rating. What if you had a different application for the lamp, i.e. lighting all around the lamp and not just in a specific direction? Then your lumens/watt would be different then if you accounted for restrike.
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Old 11-09-2007, 07:49 PM   #13
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Fishscale, do you agree with this:
Luminous efficacy is a property of light sources, which indicates what portion of the emitted electromagnetic radiation is usable for human vision. It is the ratio of emitted luminous flux to radiant flux. Luminous efficacy is related to the overall efficiency of a light source for illumination, but the overall lighting efficiency also depends on how much of the input energy is converted into electromagnetic waves (whether visible or not).

I stole this from Wikipedia and was uncertain what 'efficacy' meant. The units I am used to are Volts/meter and Watts/(square Meter) for measuring electromagnetic waves. I am not used to thinking about Lumens, luminous flux, etc.

Ok, when talking about radio transmitters and antennas there is a trick question that is used to tell those who think they know everything from those who really do. Say you have 1 watt feeding an antenna. You replace the antenna with one that has 3 dB gain (factor of 2x on power). How much power is radiated? The correct answer is 1 watt, not 2 watts! (I am neglecting losses here, which are usually trivial with most antennas.) The reason is that the gain antenna will concentrate the available power in certain directions and 'weakens' it in other directions.

With lighting we would do the same thing by putting a reflector behind the lamp. The total light emitted by the lamp is the same, but with the reflector it is 'concentrated' in a certain direction.

Anyway, my intitial post was to ask just what was restrike, and was it really a problem.

Jim
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Old 11-09-2007, 08:26 PM   #14
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I agree with you that the total light emitted is roughly the same, but I would say that restrike exists, but that it is trivial.
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Old 11-09-2007, 08:27 PM   #15
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man, you know what i really wish somebody would make--i mention this because the spiral CF's would be the right kind of bulb--is a reflector that creates a spotlight beam. a fixture thus equipped could be hung closer to the ceiling, permit less light to spill into the room and create a much nicer view from above of an open-top tank.

is there anything like that out there?
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