How many lumens do you have per square foot?

[Number21]

I recently moved my shop, at first I thought I would really need to upgrade the lighting because I was used to the big 400w MH high bay lights in my old shop. Tonight I counted up all my 8' tubes and calculated it out, I've got over 200 lumens per square foot now, where I only had about 60 in my old shop! I still plan to add to that, I have several T8 fixtures and bulbs I can install.

I'm just curious, how many lumens per square foot do you guys have in your shops?

 

[nate379]

Holy hell, do you wear sunglasses in there?

I have 40 Lumens/foot in my garage and it's plenty bright. I may put 2 more lights for a total of 6 though because when I have the door open it covers 2 of the 4.

 

[pattenp]

115 lumens/foot here.... I have 6 - 2 bulb, 96", T12 95W HO units on a 12 1/2 foot ceiling. My garage is painted all off white so I get plenty of light. I can't think of needing 200 lumens/ft or more, unless your garage has a very high ceiling and has dark colored walls and ceiling.

 

[Nostraquedeo]

I am interested in how you are coming up with your calcs for 200 Lumens per square foot.

 

[Cryptic1911]

mine arent installed yet, but i should have around 220/sf

just take the lumens output for a bulb, then multiply it by the # of bulbs, then divide by your square footage

 

[Gary S]

I never counted the little suckers. I have enough to I can see really well to get work done.

 

[FastEddieG]

(9) 2 bulb T8 fixtures from Wal-Mart
3100 lumens per bulb (18 bulbs)
650sqft
=================
~85 lumens/sqft

 

[mmhouse]

78 lumens/sf here.

It's good, but could use just a tad more at times.

 

[FlameOut]

Not sure what I have. I'm using 20 - 4' 2 bulb fixtures (40 bulbs total) My garage is right at 900 sf. I know it's bright in there/ The T-8 bulbs are 5000k if that matters

 

[FastEddieG]

Not sure what I have. I'm using 20 - 4' 2 bulb fixtures (40 bulbs total) My garage is right at 900 sf. I know it's bright in there/ The T-8 bulbs are 5000k if that matters

I think the 5000k figure is the color temperature, not lumens Lumens are generally in the thousands per 4' flourescent bulb. A 500,000 lumen bulb would be amazing! I'm guessing 2000-3000 lumens/bulb is accurate.

So with those assumptions, you are looking at a range of 89-133 lumens/sqft.

-Ed

 

[walrus]

I just had 12 8ft, 4, 4ft tube, t8 lights delivered for my 1000 sq ft shop. Should be enough but I might put some more up over my bench

 

[ddawg16]

I'm running 24 6" recessed cans with 23W CFL's....works out to about 66 lum's per sq ft....if I want more, I just have to put in a higher wattage CFL...

I am very happy with my setup....I have the light where I want it....it's easy to change color and just as easy to change wattage up or down.....

 

[Charles (in GA)]

My Lithonia MH 400 Watt fixtures are rated at 36,000 lumens each (new). I've got twelve of them, thats 432,000 lumens, and I have 3,600 sq ft, so thats 120 lumens per square foot. Bear in mind that they are mounted 15+ ft up, the floor is unfinished concrete (absorbs lots of light) and the remainder of the inside is white insulation and red primer structure. Its a decent amount of light, I think I'd be unhappy if it were less than about 100 lumens per sq ft however, in this building.

Charles

 

[Schrodingers Cat]

here's a decent calculator:
2 caveats,no factor for losses, no factor for mntg height...
if you adjust your desired fc x 1.25 it should be very close

http://www.gelighting.com/na/business_lighting/education_resources/tools_software/toolkit/layout.htm

using a 10000 ft^2 room, 32W bulbs/4 per fixture, 2400 lum/bulb, CU of 0.6 (std)
yeilds ~ 1.1 W/ft^2 for 50 fc (net 40 or so), a decent guide line for avg area lighting in a shop with extra lighting on task areas

so we can say 100 sq ft for 40 fc needs ~1.11 w/ft^2
so 3000 feet would need ~3300 W or ~104 tubes or 26 fixtures...

 

[Schrodingers Cat]

(9) 2 bulb T8 fixtures from Wal-Mart
3100 lumens per bulb (18 bulbs)
650sqft
=================
~85 lumens/sqft

it doesn't work that way, it's not linear, it's exponential...
the calculator puts that ~50 fc

 

[Schrodingers Cat]

My Lithonia MH 400 Watt fixtures are rated at 36,000 lumens each (new). I've got twelve of them, thats 432,000 lumens, and I have 3,600 sq ft, so thats 120 lumens per square foot. Bear in mind that they are mounted 15+ ft up, the floor is unfinished concrete (absorbs lots of light) and the remainder of the inside is white insulation and red primer structure. Its a decent amount of light, I think I'd be unhappy if it were less than about 100 lumens per sq ft however, in this building.

Charles

the calculator puts that ~70 fc (lumens) without factoring the losses you mentioned (LLF's, light loss factors, typically ~0.7 depending on mtg ht, wall colors, etc.) you are probably closer to 50-55...

 

[Schrodingers Cat]

this is another http://www.a-wall.com/lightcalc.php
40 fc ~ 1.1 w/sq ft, that's where the 'rule of thumb' comes from

40 fc, 100' x 100' room, 8' clg, 68 ea 4 tube (40 W) fixtures, 2.5 ft work level

68 x 4 x 40 W / (100 x 100) sq ft ~ 1.1 W/ft sq

 

[pattenp]

Well... based on the first calculator my 115 that I posted just dropped to 65 to 70.

 

[Schrodingers Cat]

Well... based on the first calculator my 115 that I posted just dropped to 65 to 70.

that's a very good figure
40 is recommended for rough work areas like mechanical shops
obviously more is needed for fine work

here's recommended fc for various tasks http://www.xtralight.com/footcandle.aspx
Units: Footcandle (fc) = (1 lumen per sq. foot)

 

[FastEddieG]

it doesn't work that way, it's not linear, it's exponential...
the calculator puts that ~50 fc

I appreciate the link, but the OP asked how many lumens per square foot.
-Ed

 

[Schrodingers Cat]

I appreciate the link, but the OP asked how many lumens per square foot.
-Ed

it's the same thing...

1 fc = 1 lumen/sq ft

 

[Bodge Garage]

9- 8' double tube T8
1- 8' single tube T8

120.33 lumens per sq foot.

I converted my fixtures to T8 (new ballasts and bulbs) the effect was extremely dramatic...seemed like double the usable light, though that cannot be true.

 

[7echo]

I try to get 60/70 at 36" AFF for 'shop' work and 100 at 36" AFF for fine work(sewing, etc). Of course, budget determines the final number.

 

[Chris Adams]

Worked it out several ways, I have about 120 per square foot. I hit 200 over the work bench though, because I have extra lighting on the bench.

 

[veno]

I have 64 per sqft...

 

[Steevo]

My lighting plan for my new shop has 14 fixtures with 4 bulbs each, at 2500 lumens per bulb (+/-). That's about 140,000 lumens in 960 square feet, for an average of 145 lumens per square foot.

 

[Ironcrow]

My working shop is 600 sq ft, 13 foot ceiling, with thirty 4 ft two tube T8 fixtures. That puts me over 200 fc; the highest listed 'detail assembly' need on the list at the website calculator linked above.

Using the feeble calculation of lumens per sq ft, I get 290.

 

[bucs012]

Just fired mine up and I have 143 Lumens or 1.6 watts per sq foot. No shadows at all. I would say 100 to 150 would be good for garage. Maybe 140-200 for work bench area.

 

[Chris Adams]

When looking at bucs012's cool garage, I noticed something. He has diffusers on his lights.
That has got to cut the light by a lot.
Anyone have numbers for the reduction from diffusers?

My lights are all bare and my wife's light meter shows about 120-210 on the floor. The 210 is by the bench where I have an additional 65 watt (500 equivalent) florescent spot light focused.

 

[bucs012]

When looking at bucs012's cool garage, I noticed something. He has diffusers on his lights.
That has got to cut the light by a lot.
Anyone have numbers for the reduction from diffusers?

My lights are all bare and my wife's light meter shows about 120-210 on the floor. The 210 is by the bench where I have an additional 65 watt (500 equivalent) florescent spot light focused.

You are right. I have taken one of them off in my shop and it puts out more light for sure!

 

[Charles (in GA)]

Here's mine lit up at night.

Charles

 

[Zrexxer]

Now I know I'm exhausted - i first read the title and thought it said "How many humans do you have per square foot?"

 

[Schrodingers Cat]

diffusers really don't absorb light, they scatter it...
so if you integrate the light output, it's the same...
just more evenly distributed
there me be minor attenuation, but not of consequence...

manufacturers produce data (photometric files) that are used for calculations
they detail a specific fixtures characteristics
40 fc is good for an area in a garage
task lighting (mobile, work lamps, etc,) is essential, especially using a lift
painting is key, 'reflectivity'
task lighting over benches of 60-80 is usually sufficient
cleaning the lamps is important...dirt WILL dimishish output significantly...

a good rule of thumb is 1.1 W/ft^2 ~ 40 fc (lumen/ft^2)
so, if you have 1.6 W fc ~ 1.6/1.1 x 40 ~ 60 fc or so...

even/uniform distribution (no shadows or dark spots) is more important than absolute intensity...

 

[Chris Adams]

diffusers really don't absorb light, they scatter it...
so if you integrate the light output, it's the same...
just more evenly distributed
there me be minor attenuation, but not of consequence...

manufacturers produce data (photometric files) that are used for calculations
they detail a specific fixtures characteristics
40 fc is good for an area in a garage
task lighting (mobile, work lamps, etc,) is essential, especially using a lift
painting is key, 'reflectivity'
task lighting over benches of 60-80 is usually sufficient
cleaning the lamps is important...dirt WILL dimishish output significantly...

a good rule of thumb is 1.1 W/ft^2 ~ 40 fc (lumen/ft^2)
so, if you have 1.6 W fc ~ 1.6/1.1 x 40 ~ 60 fc or so...

even/uniform distribution (no shadows or dark spots) is more important than absolute intensity...

Um, no, they don't just diffuse it.

There is much less ambient light after you put the diffuser on.

Check it with a light meter. We did, several times.
Huge difference.

A diffuser, in theory, only loses a few percentage points of light.
In theory.
In practice, they lose anywhere from 5-25%.
And that is before they get dusty, film covered, dirty. Which really cuts the light. We used to have to pull the diffusers in our stores every six months and clean them with soap and water, or the stores were visibly darker.

Want a simple test, and don't have a light meter? Get some fine print, the finest you can read, and read it with or without the diffuser.
Pretty obvious.
The diffuser is a 'softer' light, with less shadow. At least according to the manufacturers.

Or why it is unlawful in California, along with some other states, to put a diffuser over your headlights. Or even a crystal clear cover. When you put light through glass, plastic, whatever, you lose light.

 

[Schrodingers Cat]

Um, no, they don't just diffuse it.

There is much less ambient light after you put the diffuser on.

Check it with a light meter. We did, several times.
Huge difference.

A diffuser, in theory, only loses a few percentage points of light.
In theory.
In practice, they lose anywhere from 5-25%.
And that is before they get dusty, film covered, dirty. Which really cuts the light. We used to have to pull the diffusers in our stores every six months and clean them with soap and water, or the stores were visibly darker.

Want a simple test, and don't have a light meter? Get some fine print, the finest you can read, and read it with or without the diffuser.
Pretty obvious.
The diffuser is a 'softer' light, with less shadow. At least according to the manufacturers.

Or why it is unlawful in California, along with some other states, to put a diffuser over your headlights. Or even a crystal clear cover. When you put light through glass, plastic, whatever, you lose light.

that's why I said keeping them clean is important...
look at a manufacturers tested and certified photometric data...
total light output is ~the same...the difference is the gradient or spread...
it's more 'diffused'

how do you 'lose' light?
it can be absorbed in certain spectrums, but diffusers are designed to NOT do so...if they allow MUCH less light, a HUGE difference, as much as 25%, why do they allow them?
by removing them you could save as much as 7.5% of the nations electricity, since lighting is ~30% of all use...

look at any lighting program...do a layout with a bare tube fixture and one with a diffuser, tell me what the difference is for a given fc level...
you'll have bright spots with the bare tubes, much more even with diffusers
the average fc will be the same (integrate all output over the area)
in fact, the diffuser might be higher...more light directed downwards, rather than the sides/walls and ceilings...

 

[Chris Adams]

that's why I said keeping them clean is important...
look at a manufacturers tested and certified photometric data...
total light output is ~the same...the difference is the gradient or spread...
it's more 'diffused'

how do you 'lose' light?
it can be absorbed in certain spectrums, but diffusers are designed to NOT do so...if they allow MUCH less light, a HUGE difference, as much as 25%, why do they allow them?
by removing them you could save as much as 7.5% of the nations electricity, since lighting is ~30% of all use...

look at any lighting program...do a layout with a bare tube fixture and one with a diffuser, tell me what the difference is for a given fc level...
you'll have bright spots with the bare tubes, much more even with diffusers
the average fc will be the same (integrate all output over the area)
in fact, the diffuser might be higher...more light directed downwards, rather than the sides/walls and ceilings...

Look, light is absorbed. It becomes energy, equals heat.

No material passes 100% of light.

Even gases stop a percentage of light, as you know.

Cheap plastic diffusers stop a LOT more. That is why they get hot. And washing them every week costs more than any possible benefit.

When the energy crises (yes, I know they were mostly politically motivated, but they were still problems) MOST stores in the USA were REQUIRED to pull the diffusers.
Also required to pull roughly 50% of the bulbs.

And yes, we knew that pulling the bulbs but leaving the transformers RUNNING helps little.

It was mandated by politicians and journalists. None of which could use a VOM on the best day of their lives...

Diffusers diffuse. But there is loss.

If you want better more even, prettier, if you will, light, you use diffusers.

I use them in the house fixtures because the light looks better.

In a shop environment you can throw more light on the job without the diffusers. That's with a given amount of energy invested.

Which is what we were talking about, not how diffusers work, theory on light diffusion, quality of color (most diffusers are 'tinted' to give a more 'pleasing' light.

Tinting kills output.
Dirt on the diffusers kills output.
Spreading the light more 'evenly' means more light in the corners of the ceiling, more light on the fixture next to it, which means LESS light on the job below it.
Again, try it, debating is great fun but you have to open the mouth of the horse and count the teeth.

 

[Schrodingers Cat]

Look, light is absorbed. It becomes energy, equals heat.

No material passes 100% of light.

Even gases stop a percentage of light, as you know.

Cheap plastic diffusers stop a LOT more. That is why they get hot. And washing them every week costs more than any possible benefit.

When the energy crises (yes, I know they were mostly politically motivated, but they were still problems) MOST stores in the USA were REQUIRED to pull the diffusers.
Also required to pull roughly 50% of the bulbs.

And yes, we knew that pulling the bulbs but leaving the transformers RUNNING helps little.

It was mandated by politicians and journalists. None of which could use a VOM on the best day of their lives...

Diffusers diffuse. But there is loss.

If you want better more even, prettier, if you will, light, you use diffusers.

I use them in the house fixtures because the light looks better.

In a shop environment you can throw more light on the job without the diffusers. That's with a given amount of energy invested.

Which is what we were talking about, not how diffusers work, theory on light diffusion, quality of color (most diffusers are 'tinted' to give a more 'pleasing' light.

Tinting kills output.
Dirt on the diffusers kills output.
Spreading the light more 'evenly' means more light in the corners of the ceiling, more light on the fixture next to it, which means LESS light on the job below it.
Again, try it, debating is great fun but you have to open the mouth of the horse and count the teeth.

I ran 2 scenarios today:
100 x 100 ft room, 9' ceiling, normal reflectivity....
one with 4 x 34W bare fixture with wrap-around
one with 4 x 34W w/diffuser
~40 fc
80 fixtures bare, 82 with diffusers...~2% difference
the room with diffusers was much more evenly lit
without the wrap-around it took MORE bare tube fixtures to achieve the same level...Acuity Visual Pro was the program I used

light (in the visual sprectrum wavelengths) does not radiate much heat
you need infra-red or u-wave...
the sun posesses ALL these wavelengths, indoor lighting does not...
it's the bulbs, filiments, ballasts that do so...
hold an electronic thermometer 5' from a light, and then 6', see what the difference is...better have 5 decimal point precision...lol

I really don't know what politicians have to do with this discussion...
they are not engineers or lighting designers...

 

[walrus]

As someone who works on lights on a regular basis, how long will plastic diffusers look the way they do when they are first installed? Everyone I've ever worked on has changed color after a few years, the plastic gets brittle and I would assume that changes its properties

 

[Schrodingers Cat]

As someone who works on lights on a regular basis, how long will plastic diffusers look the way they do when they are first installed? Everyone I've ever worked on has changed color after a few years, the plastic gets brittle and I would assume that changes its properties

this is true, they get dirty, the bulbs age, etc.
they are usually good for 10 years or so, depending on type and initial quality...same thing happens to ceiling tiles, and reflectivity of the light is as important parmeter as almost anything else...

but generally you can wipe the diffuser down to clean it, where as doing so with bulbs is not as easy...and should be off...

it is better for visual acuity to have marginally less, diffused, glare free light than the slightly more, glare prone, shadowed light...
there is a reason why they are used in operating rooms, drafting rooms, and other areas of precision work...

 

[ddawg16]

Ok guys....science class time.....

A diffuser 'diffuses' light......so, yes, if you measure the light with and without a diffuser, the reading will be different....but not because the diffuser is blocking so much light.....

Lets assume a bulb puts out 100 lums of light....if you direct that light to a single point, you will measure 100 lums at a specific distance....(for reference, lums to be accurate must be stated at a given distance). Now measure the lums away from the point of light.

Now, take that same light and put in a diffuser. Measure the light again at the same points.....the measurement at where the original point was will be less....and the light at the off point position will be higher.

Why? Because we are 'diffusing' the light....in other words, spreading it around....you have the same amount of total light, only the intensity at a given point is less....

Unless you have a really crapy diffuser, I would be surprised if more than 5% of the light is being blocked.

Heat....the diffuser is NOT heating up because it is blocking the light....it is heating up because it is in close proximity to the bulb and is preventing heat from escaping....you would get the same result with a clear piece of glass.

Any questions students?

BTW....if your going to tell me I don't know what I'm talking about, then you need to include technical data and references to any rebutal.