Lumens per sq/ft?

[johnday]

Going to redo a 14'X28' bay in my barn with LED lighting. I've read quite a few articles on line, and a number of different opinions.
How many lumens per sq/ft is a good rule of thumb. I've read 30, and I've read 70, and everything in between.
That bay will be used for occasional carpentry, but mostly for some light mechanic stuff for a pickup, and compact 35HP tractor. Mainly interested in good lighting at one end out to about 14', and the remainder just average garage lighting.

 

[cybrdyke]

Hi John,
Unfortunately, you cant use lumens per square foot as a criteria for good lighting. If you've read something that suggests a certain lumens per square foot as a good amount of light, you can consider that source as non-credible because they dont know what they're talking about. Also, there is no "rule of thumb" for lumens per square foot.
I'll try to demonstrate... imagine a room that's 10' x 10' where you have a 1000 lumen light source. You would think that you have 1000 lumens per 100 square feet, or 10 lumens per square foot. Now...raise the ceiling up to 20'. You still have 10 lumens per square feet, but the light source is much further away. Now, raise the ceiling to 50'. Do you still have the same amount of light? No.
Also extremely important is the source of the light. Is it a light bulb that shines in 360 degrees, or is it a spot light that only shines in one direction? Where are your lumens going? Are the walls a shiny white surface or a rough cinder block surface. Are your lumens reflecting off the walls or not?
All of these things and many many many others determine how much "light" you will have in your space.
The correct thing to do is to get a lighting layout for your space. For this, you'll need to supply the dimensions, HxWxL, the wall, floor, and ceiling surface materials, and the expected use of your space (which you've done). Get this info to someone that can do a layout for you and you'll have a perfect answer.
If you look at the stickies at the top of the lighting and electrical section of the forum, there is a lighting layout thread. There may already be a layout there that aligns with your dimensions. It's might already be done for you!
Sorry to be a downer on your request, but you'll be much better off if you get a layout done.
Good luck,
CD

 

[Toomanytools?]

Going to redo a 14'X28' bay in my barn with LED lighting. I've read quite a few articles on line, and a number of different opinions.
How many lumens per sq/ft is a good rule of thumb. I've read 30, and I've read 70, and everything in between.
That bay will be used for occasional carpentry, but mostly for some light mechanic stuff for a pickup, and compact 35HP tractor. Mainly interested in good lighting at one end out to about 14', and the remainder just average garage lighting.

You might be thinking of Foot Candles, many of the posts refer to the amount of FC at a working height of 3 feet ( common work bench). This also varies but a consciences seems to fall at the 100FC for tasks such as wood working or assembly, auto work. You can use this lighting tool to help. http://www.visual-3d.com/tools/interior/ The tough part is figuring out the light to use in the program. There are variables as to the reflectivity in your space and objects in the room, like a large RV blocking some of the light. I have seen average lumens per square foot info, but I'm not sure it's that easy.

 

[johnday]

You two have given me some good advice. I'll check out that other thread, and the link.

 

[johnnyradiant]

Lumens are stamped everywhere in specs, and I can't equate that number to giving much reference. I work with projectors and lumens are the goto spec. Even different brands tested on the same screen in the same room with the same clips and images will yield different results despite being spec'd at the same lumen output. It's a frustrating marketing spec partly because there is more than one way to come up with the number in a lab, and also because there are other variables at play with some of them the examples TooManyTools points out in his post.

 

[johnday]

Ya, sounds like you've modded some headlights. You're not kidding, the specs are all over, I was hoping there'd be an easy way with residential type lighting. Oh dopey me.

 

[justinthurn]

I'll give you some real world examples. My garage is 10' ceiling, 24x30 with can lights. 30 lumen per SF and does good for a garage. I would bump that to 50 if I was wrenching. My office with 10' ceilings is about the same different can lights and different layout but same result and With the help of daylight it is great but I wish it was about 50 also. My shop is 50x60x16. I do not have all the lights in but it is going to be about 100 lumen per SF which may be too bright for general use but will be very nice for woodworking and wrenching I used led high bay fixtures and have not finished the ceiling or walls yet. I'm seeing a correlation between ceiling height and the amount of light. Looks like 30-70 lumen per SF would be ok for up to 12' high and 50-100 lumen per SF for 10-18' high. Notice that the range can mean up to double the amount of light on the high end vs low end.

Sent from my SM-G960U using The Garage Journal mobile app

 

[redidbull]

I have people coming in looking for light bulbs and are so hung up on how many lumens this lamp is or that bulb is. I see difference more in light bulb of soft white vs daylight. No one I ever talk to even knows what a lumen is. Jim

 

[Platonic Solid]

The world would be a much brighter place if ppl would stop using "lumens per SF" as a valid unit of measure. It's not! CD eloquently explained the issue, then justinthurn comes in with more "lumens per SF" disinformation. ARG! It's like trying to say how many square feet are in a gallon of milk. [/rant]

 

[pattenp]

It's like trying to say how many square feet are in a gallon of milk. [/rant]

At one micron deep it's 40,745 sqft. +- a sqft.

 

[ddawg16]

Lots of good info above...especially from cybrdyke

Lets take my garage for example....the 1st floor is 20x25. I have 18 recessed cans that now have LED (75w equiv) trims in them. I 'did' have CFL's with a mixture of 75w-100w equiv bulbs. Most of the CFL's were 4000-5000K range...the LED's are warm white...around 2700k. I would have preferred a 4000K range...but...these LED trims were on sale at Costco for $4/ea....basically cheaper than the open trims I was planning to buy.

The color of the light makes a big difference. 4000K would be a bit brighter....but, I will say the LED trims have a more uniform light.

With all that said...where I was going was....as the others above pointed out, there are a lot of factors. My lights are set up in 3 zones....I only turn on the zone I'm working in. 90% of the time I have more than enough light. But I'm also a fan of task lighting. I have extra lights over certain work areas as needed.

Right now I'm shopping for a LED panel to put above my table saw. When I did the original layout....I didn't put any lights where the garage door was when it was up. At night when I'm in the garage....and the door is down...that area is a little dark. I think a flat panel would work great.