# Foot candle output lower than acceptable



## Podagrower (Mar 16, 2008)

I'm looking for ideas to solve a problem. I have an installation where the measured foot candles are lower than the computer models. 3 computer models using 2 different programs show approximately 40% more foot candles than 3 different foot candle meters are showing. 

So far, 2 different electrical contractors and the electrical engineer have looked at the install and found no issues. Measured voltage at panels and fixtures are well within tolerance for the ballasts, voltage drop is almost non existent, the building is served by it's own POCO transformer, there are probably 200 fluorescent fixtures on the 277 system, and maybe 50 computers on the 120 side, each circuit is a dedicated neutral, so I can't imagine a harmonic issue. 

I'm looking for ideas on what the problem is. I think we have eliminated: voltage, neutrals, temperatures, surface reflectivity, and mounting heights as possible causes. I'm willing to entertain just about any theory at this point.


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## wildleg (Apr 12, 2009)

were the bulbs burnt in properly ?

are the fixtures connected to an energy management or dimming controller ?

are the ballasts dimmable (are they set to max) ? (it's easy to have the settings wrong in some dimming panels)


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## 99cents (Aug 20, 2012)

You might go back and do an old fashioned zonal cavity calc to verify the software results. What software are you using?


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## Podagrower (Mar 16, 2008)

wildleg said:


> were the bulbs burnt in properly ?
> 
> are the fixtures connected to an energy management or dimming controller ?
> 
> are the ballasts dimmable (are they set to max) ? (it's easy to have the settings wrong in some dimming panels)


All but one office area were burnt in extremely well. The office area is controlled by occur sensors, and those bulbs show significant blackening, but changing them to new bulbs did not result in any significant change.

Most of the fixtures are controlled by a lighting control panel, but it has no dimming capabilities, and we bypassed it completely (used an extension cord to connect a group of fixtures to a 120v circuit with no change in levels)

There are a few dimmable fixtures, but the trim pots are all the way up, bypassing the dimmer produces no change.


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## Podagrower (Mar 16, 2008)

99cents said:


> You might go back and do an old fashioned zonal cavity calc to verify the software results. What software are you using?


I don't remember the software name the EE and lighting supplier used, but the Architect was satisfied with it, the lighting supplier also used a second program and got the same results.

Our "control" is a 10x14 room with a single 3 lamp F32T8 parabolic mounted at 10'. Computer spits out 56, the EE and lighting supplier's brains spit out 50, but we have 25. (Rough numbers from memory). Wall reflectivity set at 30 in the computer models, closer to 50 in reality, white acoustic ceiling, dark carpet on the floor.


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## 99cents (Aug 20, 2012)

I'm betting on a design issue, not an electrical one. The old adage about software - garbage in, garbage out - might be at play here. Input values might be overstated, photometry might even be off. If you supplied and installed fixtures and lamps according to spec, let the lighting agent and engineer fight it out.


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## daveEM (Nov 18, 2012)

^^ What 99 says. The meters are correct and I might have used two. Three and you're really checking things out.


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## dspiffy (Nov 25, 2013)

99cents said:


> I'm betting on a design issue, not an electrical one. The old adage about software - garbage in, garbage out - might be at play here. Input values might be overstated, photometry might even be off. If you supplied and installed fixtures and lamps according to spec, let the lighting agent and engineer fight it out.


If it ends up being anything other thing this, I'd really love to hear.


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## wildleg (Apr 12, 2009)

unless the lenses you got are totally screwing the light, I agree with ^ those guys, cause it sounds like you've covered all the other bases

(BTW, do the fixtures have good reflectors ?)

lenses and reflectors can make a huge difference.


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## Podagrower (Mar 16, 2008)

Parabolic lenses, no special reflector behind the bulbs, which I know would help. So far 2 of the existing fixtures have been removed, 1 sent to the manufacturer, 1 taken to the lighting distributor, both produced the expected light levels when installed in other buildings. The EE and lighting supplier have been unable to provide a solution in 6 months, and I'd like to have a resolution.


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## dspiffy (Nov 25, 2013)

So when you measure one fixture directly, it measures lower output in this building than in the other two buildings?


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## wildleg (Apr 12, 2009)

Podagrower said:


> Parabolic lenses, no special reflector behind the bulbs, which I know would help. So far 2 of the existing fixtures have been removed, 1 sent to the manufacturer, 1 taken to the lighting distributor, both produced the expected light levels when installed in other buildings. The EE and lighting supplier have been unable to provide a solution in 6 months, and I'd like to have a resolution.


wow. you done did your homework. Now I'm a little confused - are you saying it is (a) definitely a design issue or are you saying (b) they actually aren't putting out the same amount of light in the installed building ? I'm seeing a, but if it's b then it shouldn't be too hard to find the culprit (?)


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## wcord (Jan 23, 2011)

Did the other buildings have the same color floor and office furniture? 
Not that the difference should account for such a large decrease in output
Grasping at straws on the design side.


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## 99cents (Aug 20, 2012)

This has to be a design issue. Any half a$$ed lighting designer should be using maintained lumens, not initial, and allowing for dirt depreciation. A new, clean fixture with new lamps should be giving you higher readings than your software. Your software should be giving you your lumens a year or two from now, not today.

I hope this wasn't a design build because this is going to take some money to rectify.


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## 99cents (Aug 20, 2012)

Podagrower said:


> Parabolic lenses, no special reflector behind the bulbs, which I know would help. So far 2 of the existing fixtures have been removed, 1 sent to the manufacturer, 1 taken to the lighting distributor, both produced the expected light levels when installed in other buildings. The EE and lighting supplier have been unable to provide a solution in 6 months, and I'd like to have a resolution.


Something's not adding up here. If this is a deep cell parabolic your light levels are highest directly below the fixture and fade out quickly towards the perimeter. The only thing I can suggest is to isolate one fixture and attempt to compare your readings to the lab photometry.


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## Podagrower (Mar 16, 2008)

dspiffy said:


> So when you measure one fixture directly, it measures lower output in this building than in the other two buildings?





wildleg said:


> wow. you done did your homework. Now I'm a little confused - are you saying it is (a) definitely a design issue or are you saying (b) they actually aren't putting out the same amount of light in the installed building ? I'm seeing a, but if it's b then it shouldn't be too hard to find the culprit (?)


That is what the manufacturer and designer are saying. Nobody else was at their facilities to witness the testing. I really didn't want to think that they would both lie, but I'm really starting to question their results now.


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## Podagrower (Mar 16, 2008)

wcord said:


> Did the other buildings have the same color floor and office furniture?
> Not that the difference should account for such a large decrease in output
> Grasping at straws on the design side.


I do not know about the manufacturer's space, I assume it to be a "clean" room. The designer's office space has lighter colored walls and flooring, but it would be a heck of a straw grasp to double the foot candles.


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## Podagrower (Mar 16, 2008)

99cents said:


> This has to be a design issue. Any half a$$ed lighting designer should be using maintained lumens, not initial, and allowing for dirt depreciation. A new, clean fixture with new lamps should be giving you higher readings than your software. Your software should be giving you your lumens a year or two from now, not today.
> 
> I hope this wasn't a design build because this is going to take some money to rectify.


No, not design build, thankfully.


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## Podagrower (Mar 16, 2008)

Oddly enough, I started playing around with some free foot candle calculators online. It helps a lot. I can't get the foot candles with a computer that they have, either in their design or their test. The software I'm using kicks out a number much closer to what we are actually seeing in the field.


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## 99cents (Aug 20, 2012)

I appreciate a guy who likes to walk away from a job well done but is this really your problem? An engineer who depends on a lighting supplier to do his layouts for him is going to find himself in deep chit sooner or later. If you installed spec fixtures according to the drawings, isn't your job done?


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## HARRY304E (Sep 15, 2010)

What type of lamps are they "Color temperature"?

Depending on the "Color temperature" such as 4100K 3500K , 

There are higher lumen output lamps available and that could be what they used to get their calculations.

Also in the offices with the occ sensors, those fixtures should have program start ballasts in them because of the constant switching on and off, also time is needed for those lamps to warm up from a cold start.

The temperature in the room will be higher than at the light fixture sitting in a dropped ceiling, it could be 70f in the room and only 65f in the ceiling.


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## wildleg (Apr 12, 2009)

would it be possible to get the manufacturer to send out a field rep to do the lighting levels ? this might answer a lot of questions.


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## 99cents (Aug 20, 2012)

Podagrower said:


> Oddly enough, I started playing around with some free foot candle calculators online. It helps a lot. I can't get the foot candles with a computer that they have, either in their design or their test. The software I'm using kicks out a number much closer to what we are actually seeing in the field.


There you have it. If you really want to bring this to a head, take a typical room and ask a completely different engineer to lay it out for you according to the design lumens. Make sure he is an IES member and does his layouts in house. It might cost you a few bucks but it sounds like this is really bugging you.


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## dspiffy (Nov 25, 2013)

99cents said:


> I appreciate a guy who likes to walk away from a job well done but is this really your problem? An engineer who depends on a lighting supplier to do his layouts for him is going to find himself in deep chit sooner or later. If you installed spec fixtures according to the drawings, isn't your job done?


Sounds to me like he's getting, from the customer: "These are dimmer than spec, you did something wrong" and trying to either rectify the situation or prove otherwise.


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## 99cents (Aug 20, 2012)

dspiffy said:


> Sounds to me like he's getting, from the customer: "These are dimmer than spec, you did something wrong" and trying to either rectify the situation or prove otherwise.


It does sound like a case of guilty until proven innocent, doesn't it?


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## dspiffy (Nov 25, 2013)

One of our commercial tenants was furious with me last week because we upgraded the building to LED and he SWEARS the LEDs are dimmer. They're noticeably brighter, but there's a lot less glare from the fixture, which I suppose makes him think they're dimmer.


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## Podagrower (Mar 16, 2008)

HARRY304E said:


> What type of lamps are they "Color temperature"?
> 
> Depending on the "Color temperature" such as 4100K 3500K ,
> 
> ...


Color temp is 3500K, one room has been changed to 4100K with not any more improvement than what you would expect.

Whole heartedly agree with the program start, but not being the designer, that is out of my hands. The lamps have always been on for at least 15 minutes before any readings began.

Ambient temperature was something looked into, room temp was raised from 75 to 80 and held for 15 minutes without an appreciable increase in foot candles. Also, we made sure the AC is not blowing across the fixtures.


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## Podagrower (Mar 16, 2008)

dspiffy said:


> Sounds to me like he's getting, from the customer: "These are dimmer than spec, you did something wrong" and trying to either rectify the situation or prove otherwise.





99cents said:


> It does sound like a case of guilty until proven innocent, doesn't it?


I'm kind of embarrassed for the Architect and Engineer who can't seem to find an answer to the problem. I've been thrown under the bus since the beginning (It must be a loose neutral, voltage drop, MWBC, you name, I've heard it). Now that all those issues have been ruled out, I'd like to find the real problem and solve it. Even though it is not my problem.


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## dspiffy (Nov 25, 2013)

Do the fixtures LOOK dim do your eyes or anyone else's eyes?

Do the rooms?

I've only ~10 projects of commercial lighting design, my lighting design background is in theatre. In planning each of the projects I did not use software, meters, formulas, or anything other than my eyes and common sense. In every case so far it has worked out how I assumed, or better. 

If something is wrong with the fixture, wiring, etc, you should be able to see it.

For someone to bring this up, either the fixtures have to look dim to the naked eyes, or the rooms themselves have to look dimmer than what they expected to the naked eyes.


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## HARRY304E (Sep 15, 2010)

Podagrower said:


> Color temp is 3500K, one room has been changed to 4100K with not any more improvement than what you would expect.
> 
> Whole heartedly agree with the program start, but not being the designer, that is out of my hands. The lamps have always been on for at least 15 minutes before any readings began.
> 
> Ambient temperature was something looked into, room temp was raised from 75 to 80 and held for 15 minutes without an appreciable increase in foot candles. Also, we made sure the AC is not blowing across the fixtures.


These are 3300 lumens https://isabelleslighting.com/light...en-linear-fluorescent-t8-800-series-medium-bi

These are 2400 lumens http://www.1000bulbs.com/product/99666/EIKO-06749.html

Both work in the same fixture.


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## Ragin Cajun (Nov 20, 2013)

Could you give the exact catalog number, brand, etc. of the fixture?

Ballast nameplate?

Actual lamp label info?

Then one can plug into one's program of choice. I use my own custom spread sheet and Visual photometrics computer program and haven't had problems (yet!).


The ballast actually shipped/installed can make a huge difference vs what was speced or ordered. Ballast factor is the key. Perhaps you were stuck with CCC ballasts (cheap china cr**). Lots of them out there, including fakes/flakes of all sorts.

The lamps actually installed in the fixture vs lamp specified can also make a big difference.

I generally spec both the ballast and lamp. I review the shop drawings with a fine toothed comb. Vendors absolutely HATE me. I have yet to not reject all or part of the first submittal - lighting, panelboards, etc. - on any project. On one project the first submittal was for fixtures with 60% efficiency vs the 91% I specified!!! Took three submittals before they finally sent lamp and ballast shop drawings. 

Lumen meters could be another issue. I had the opportunity to check mine to a high end, multi thoudand dollar meter and I believe mine read high by ~10%, but not near as far off as you are seeing.

Buried in all the data is the real reason.

RC


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## Knightryder12 (Apr 4, 2013)

Podagrower said:


> I'm looking for ideas to solve a problem. I have an installation where the measured foot candles are lower than the computer models. 3 computer models using 2 different programs show approximately 40% more foot candles than 3 different foot candle meters are showing.
> 
> So far, 2 different electrical contractors and the electrical engineer have looked at the install and found no issues. Measured voltage at panels and fixtures are well within tolerance for the ballasts, voltage drop is almost non existent, the building is served by it's own POCO transformer, there are probably 200 fluorescent fixtures on the 277 system, and maybe 50 computers on the 120 side, each circuit is a dedicated neutral, so I can't imagine a harmonic issue.
> 
> I'm looking for ideas on what the problem is. I think we have eliminated: voltage, neutrals, temperatures, surface reflectivity, and mounting heights as possible causes. I'm willing to entertain just about any theory at this point.


Where are you measuring the footcandle level at in the room? The reason I ask is most of the time when doing the photometrics the program is run with the light levels at 30" AFF to see what will be at a typical desk height. So I would check that. Also I saw in one of your later post, if you are measuring at the floor, you said there was dark carpet and you would be surprised at how much a dark soft surface can effect the readings from a light meter.
One more thing, what kind of meter are they measuring the footcandles with? They need to be professionally calibrated and the engineer or architect should have the certificate of calibration. They should be calibrated every year btw.


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## Knightryder12 (Apr 4, 2013)

I just ran a 10'x14' room with the settings that you stated in a previous post with 1 - 3 lamp parabolic at 10'-0" and I am getting an average of 32.4fc with a max of 48.6fc and a minimum of 20.1fc. The max to min is 2.4:1 (should be lower).
In my opinion the engineer could never get 56fc's and they should have used 2 - 2 lamp fixtures in this size room for a more even light distribution.

The program I use is Visual from Lithonia.


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## Ragin Cajun (Nov 20, 2013)

Knightryder12 said:


> I just ran a 10'x14' room with the settings that you stated in a previous post with 1 - 3 lamp parabolic at 10'-0" and I am getting an average of 32.4fc with a max of 48.6fc and a minimum of 20.1fc. The max to min is 2.4:1 (should be lower).
> In my opinion the engineer could never get 56fc's and they should have used 2 - 2 lamp fixtures in this size room for a more even light distribution.
> 
> The program I use is Visual from Lithonia.


 Sounds about right. I distain designing with only one fixture in any office, the min/max ratio becomes too high. RC


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## chicken steve (Mar 22, 2011)

No because the electrician is always the fall guy, the target for all_ influences _ 99

~CS~


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## Podagrower (Mar 16, 2008)

Ragin Cajun said:


> Could you give the exact catalog number, brand, etc. of the fixture?
> 
> Ballast nameplate?
> 
> ...


Not willing to post that info in a public forum, but if you want to run it thru your software, I'll PM you the specifics.


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## Podagrower (Mar 16, 2008)

Knightryder12 said:


> Where are you measuring the footcandle level at in the room? The reason I ask is most of the time when doing the photometrics the program is run with the light levels at 30" AFF to see what will be at a typical desk height. So I would check that. Also I saw in one of your later post, if you are measuring at the floor, you said there was dark carpet and you would be surprised at how much a dark soft surface can effect the readings from a light meter.
> One more thing, what kind of meter are they measuring the footcandles with? They need to be professionally calibrated and the engineer or architect should have the certificate of calibration. They should be calibrated every year btw.


The "control" room is measured at 30" because it has a desk. The floor measurements are from rooms where the floor is the work surface (simply because there isn't another work surface in those rooms).

The 2 actual light meters were a Fluke of unknown calibration that was 10% higher consistently than the meter that had a calibration certificate.


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## rdevarona (Feb 23, 2010)

I'm really curious to find out what the reason for this will end up being. Did you ever see any of the lighting layouts that were done for this space or do you know what the values for light loss, lumens per lamp and surface reflectance were? 

I suppose that the IES model that was used for the fixtures could also be to blame, but that's a long shot. It would be easy to compare the expected output for for this fixture's IES model with that from a similar fixture from another manufacturer.

I agree with Ragin Cajun, knowing what inputs went into the simulations will help you understand why you have that particular output. I've seen all sorts of tricks used to sell lighting projects and they usually involve over/understating inputs. A well designed project will measure higher than what was calculated if the input conditions are accurate.


Regards,

rdv


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## zen (Jun 15, 2009)

This is an interesting subject . If its build to spect I think the best thing to do is install and let them test lumens. If they arent enough then thats up to them to make it right for the customer. I think if u keep questioning how it could be something u may need to do they will push this off on u. Make one wrong comment or thought as to why and there will be problems.. once we did an elev. Shaft. Elev. Tech said it wont pass lumens test. My sup said change the lights. I said stick to plans and let designers deal with it. We still failed. Designers said no proof their design would have failed. We know it would have. We had to pay 2k reinspect fee.

learning to learn


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## Podagrower (Mar 16, 2008)

Well, we finally have a winner. Last night I was told that we would be swapping the existing fixtures for the same fixture, but with 4 T5HO bulbs instead of T8.


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## drspec (Sep 29, 2012)

Podagrower said:


> Well, we finally have a winner. Last night I was told that we would be swapping the existing fixtures for the same fixture, but with 4 T5HO bulbs instead of T8.


On who's dime?


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## 99cents (Aug 20, 2012)

I'm betting the engineer, distributor and lighting rep all attend the same country clu ... erm ... church.


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## cdnelectrician (Mar 14, 2008)

I had a very similar problem last year. After numerous meetings with the fixture manufacturer and the lamp manufacturer (phillips) it was found that there was a slight airflow around the lamps because they were installed in a plenum ceiling. This small amount of airflow actually cooled the lamps enough that the light output was reduced by 20 percent or so.

The fixtures were spec'd and listed for use in a plenum ceiling however the trims were not, we changed the trims to covered trims to prevent any airflow around the lamps and this solved the issue. You might try looking at this angle...the lamps in question were PL226 lamps.


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## Ragin Cajun (Nov 20, 2013)

Which fixture did they deside to go with?

RC


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## Podagrower (Mar 16, 2008)

Ragin Cajun said:


> Which fixture did they deside to go with?
> 
> RC


4 Lamp T5HO, same stupid parabolic. But it will keep the look they have, and get the light they want.


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## Ken2972 (Dec 23, 2013)

I had an issue similar. Turns out we had too much air flow in the ceiling above the fixtures. I ended up taking a metal duct tape and taped up all the holes in the fixtures to keep the air out. Basically our bulbs were not getting warm enough, because of the air flow. Dont know if that helps or not.


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## teufelhounden91 (Jul 8, 2012)

What temperature color are you using? 3500k, 4100k, 5000k?

I'm curious what the difference in metrics would be vs the color you use. F32t8 Spx50s are very bright compared to a standard f32t8 830 but I don't know about the difference in actual foot-candles.


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## Southeast Power (Jan 18, 2009)

Podagrower said:


> Well, we finally have a winner. Last night I was told that we would be swapping the existing fixtures for the same fixture, but with 4 T5HO bulbs instead of T8.


Wow,
Those lamps are about 54 watts each.
Sounds like a lazy solution. 

I think you have some environmental issues if the fixtures operated as designed offsite.


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## Electric_Light (Apr 6, 2010)

Podagrower said:


> Well, we finally have a winner. Last night I was told that we would be swapping the existing fixtures for the same fixture, but with 4 T5HO bulbs instead of T8.


Ummmm, did sales guy give some type of ROI/energy savings/PBP pitch? 
You might satisfy the FC level with the new proposal, but did you tell them it is at the expense of using 2-3x the electricity? :laughingdepending on if the T8 fixtures were normal or High BF)

With the 4 lamp 54W T5 setup, you're at 18,600 mean LM at the lamps with 236W input. This is about what you need to match the mean lumen of a 400W probe start MH fixture with an average grade fixture. 

With the original 3 lamp T8 setup: 
3 lamp T8 with high ballast factor would be 10,000 @ 110W 
3 lamp T8 with a regular ballast is 7450 @ 82W 

Standard T5s are always 1.0 multiplier and the ballast is actually 1.0 unless it says otherwise. 

Standard T8s are 0.87. T8 H ballasts are 1.1 to 1.2. If photometric values say at BF=1, the actual will be 87% of that.




teufelhounden91 said:


> What temperature color are you using? 3500k, 4100k, 5000k?
> 
> I'm curious what the difference in metrics would be vs the color you use. F32t8 Spx50s are very bright compared to a standard f32t8 830 but I don't know about the difference in actual foot-candles.


Zero. Current standards don't recognize alternate rating using night vision (scotopic lumens). LED industry likes to push the 5,700K so they can claim higher equivalent watt to inflate their performance. SPX65 lamps have the same effect.


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## Electric_Light (Apr 6, 2010)

Ragin Cajun said:


> I generally spec both the ballast and lamp. I review the shop drawings with a fine toothed comb. Vendors absolutely HATE me. I have yet to not reject all or part of the first submittal - lighting, panelboards, etc. - on any project. On one project the first submittal was for fixtures with 60% efficiency vs the 91% I specified!!! Took three submittals before they finally sent lamp and ballast shop drawings.
> 
> RC


In light of the Venture Capital LED manufacture Switch's collapse, I would strongly recommend purchasers to be more demanding. 

Qualifying manufacturer shall have been manufacturing power supplies or ballasts commercially for a minimum of five years with a good track record. Five year minimum shall be extended to the actual manufacturer. 

Life rating shall be the L90 life in applications traditionally served by linear fluorescent lamps. 

The use or, lack of lamp lumen depreciation compensation such as Lithonia N80 shall be explicitly disclosed.

LED system warranty shall not be pro-rated.


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