led lighting

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eagle2025

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Location
Fayetteville, NC 28306
Occupation
Retired electrician
We are re purposing a elementary school into a church. We are going to replace the old CFL fixtures with LED 2 x 2 drop in fixture. Can I use the formula=sq ft / wattage of the fixture?
Thanks
 
It is difficult to get an accurate "like for like" lighting level when transitioning from florescent to LED as a direct conversion doesn't seem to be available or even comparable. Also a change from classroom lighting level to an assembly type occupancy has a different Lumen requirement. Lumens, kelvin level, and color of the LED all will play a role in visual perception of brightness to the occupants that generally wasn't a consideration with the florescent lights. Recently did a retrofit and existing florescent was 4500W but even going down to 3200w LED equivalent was "brighter" than the florescent.
 
We did a fixture/fixture replacement a few years ago. The originals were 300-watt incandescent. Most had a CFL of some sort or nothing at all installed. We asked about getting a layout done but time wise it was easier to replace with 2x2 LED troffer. I think you could have performed surgery at floor level. Overkill.
 
there are plenty of online calculators to get you a foot candle reading, if that is what you are looking for. You could get yourself a cheap light meter on amazon and get a lumens reading of the existing condition and look for light fixtures with a similar output.

People will shun me for saying this, but LEDs are not brighter than any other light source, they just provide a wider range of light levels and a cleaner looking light output. Lumens are the number you need to look at now instead of wattage. Additionally, we can manipulate LEDs in ways that we couldn't with older styles and therefore companies create fixtures with glare that we are not comfortable with so we argue that the lights are "too bright".
 
Rock86 said:
there are plenty of online calculators to get you a foot candle reading, if that is what you are looking for. You could get yourself a cheap light meter on amazon and get a lumens reading of the existing condition and look for light fixtures with a similar output.

People will shun me for saying this, but LEDs are not brighter than any other light source, they just provide a wider range of light levels and a cleaner looking light output. Lumens are the number you need to look at now instead of wattage. Additionally, we can manipulate LEDs in ways that we couldn't with older styles and therefore companies create fixtures with glare that we are not comfortable with so we argue that the lights are "too bright".
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You can get a Lux meter for a smart phone that will give lumens. Agree that it is perception thus the quote around "brighter". Every source I tried to get a clean comparable conversion Watt to lumen was useless. If not using a design program that specifically works for LED that will give K value, Lumens, and Color at a given ceiling height, working height, and diffusion angle of the light, that will show number of fixtures/sqft., it will be mostly a guess. Best option then would be to get the adjustable fixtures that you can change both the color and lumens. Been using these mostly for resi. lighting as inevitably the HO will say it's "too bright" or "too white or yellow", they do have some that are dimmable but be sure the dimmer is rated for LED.
 
Fred B said:
You can get a Lux meter for a smart phone that will give lumens. Agree that it is perception thus the quote around "brighter". Every source I tried to get a clean comparable conversion Watt to lumen was useless. If not using a design program that specifically works for LED that will give K value, Lumens, and Color at a given ceiling height, working height, and diffusion angle of the light, that will show number of fixtures/sqft., it will be mostly a guess. Best option then would be to get the adjustable fixtures that you can change both the color and lumens. Been using these mostly for resi. lighting as inevitably the HO will say it's "too bright" or "too white or yellow", they do have some that are dimmable but be sure the dimmer is rated for LED.
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Check out a program DIAlux. They used to all full function for free, meaning you could download a manufacturers IES file and load it a design. The free version now limits the user to using only approved IES files (which are a lot) and then just manipulate the values to match the fixture you are looking to install.

Example: if you want a Metalux 2x2 with 4230 lumes, 45W, 3500K, just find a 2x2 and change the characteristics.
 
eagle2025 said:
We are re purposing a elementary school into a church. We are going to replace the old CFL fixtures with LED 2 x 2 drop in fixture. Can I use the formula=sq ft / wattage of the fixture?
Thanks
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What kind of cfl fixtures?

What kinds of rooms are they, and what purposes?

I spearheaded an upgrade at our church/school a couple of years ago, and the lighting was not the same in every area.
 
Rock86 said:
People will shun me for saying this, but LEDs are not brighter than any other light source, they just provide a wider range of light levels and a cleaner looking light output.
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It depends on how you are comparing them. Watt for Watt they are certainly brighter.
 
ggunn said:
It depends on how you are comparing them. Watt for Watt they are certainly brighter.
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It would be silly to compare them Watt for Watt, that is why I said we need to use Lumens. We have been born and bred to recognize light output in terms of Watts, but we can't do that any more with LED. two LED bulbs could say 10W, but could have different Lumen outputs.
 
Rock86 said:
It would be silly to compare them Watt for Watt, that is why I said we need to use Lumens. We have been born and bred to recognize light output in terms of Watts, but we can't do that any more with LED. two LED bulbs could say 10W, but could have different Lumen outputs.
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LED equivalent bulbs are around 100 lumens per watt. Incandescent is about 10 lumens per watt. Divide by 10 and you have your LED wattage. It's close enough. If you need to be more precise, you're too picky in my opinion. (Applies to LED equivalent bulbs only)

Eagle2025, If you are going from a CFL U-bulb to LED troffers, my recommendation is a 3000 or 4000-lumen output 2x2 LED fixture. Replace one of the fixtures and ask the Church Trustee's if they think it's bright enough. It's a church, so lots of older people with poor eyesight. If you get a light meter like other commenters have suggested, google "IES lighting recommendations" for values to target.

My real suggestion, figure out what brand of fixtures you like and contact a local lighting rep. They will produce a photometric study free for you if you purchase their fixtures. I like Lithonia (Acuitybrands), personally.
 
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