Candles vs lumens

[Perfectstranger]

Trying to work up a lighting diagram, reading thru threads and it seems that these terms are used alot, but not together. When you research lights it lists lumens, so is there a specific lumens per square foot equation?

 

[cybrdyke]

is there a specific lumens per square foot equation?

No.
It's confusing, I'll admit.

Lumens is the amount of light produced by the source, typically a lamp.

Here's the confusing part....
Foot-candles is defined as "lumens per square foot". (This does NOT mean that you can divide your total lumens by your total square footage.) "Lumens per square foot" is a measure of illuminance, or how much light has fallen on a surface.

In other words, we know how many lumens are produced, in a lab, by a 60w light bulb (approx. 800). But, when we are measuring foot candles, we are measuring how lumens are cast onto a 1'x1' area. They are two completely different things and, almost always, folks get it wrong.
"Lumens" from a lamp is not used in the calculation "Lumens per square foot".
My brain hurts.
CD

 

[Showkey]

Perfect stranger..............If you were actually measuring the light reaching a surface you would be measuring LUX or foot candles. 1000 lux is 92.9 FC.

Example bench top lighting for detailed work one might want 750 to 1000 LUX on the work surface.

 

[bczygan]

Lumens is what you have at the source.

Light levels fall off with distance.

Foot candles are the light level at the object being illuminated. Distance from the source can vary, which changes the FC level.

https://en.wikipedia.org/wiki/Inverse-square_law

http://www.theledlight.com/lumens.html

 

[Perfectstranger]

So to sum up what I think I've learned is the specs that I might go d at HD.com really don't tell me how well a light may light an area but just that it may be more light then another.

In short I can not figure I have 525 square feet and to light that space for general lighting I should have x lumens. If I want to do detail work I may need ylumens.

Am I trying to make this simpler then it is?

 

[cybrdyke]

So to sum up what I think I've learned is the specs that I might go d at HD.com really don't tell me how well a light may light an area but just that it may be more light then another.

That's right, because HD specs dont tell which direction any of those lumens are going. So, all you can do is compare fixture A to fixture B. To see where the light is going and how to properly space the fixtures, you need someone with a computer program to do it for you. There's a few forum members who might be willing.

In short I can not figure I have 525 square feet and to light that space for general lighting I should have x lumens. If I want to do detail work I may need ylumens.

Am I trying to make this simpler then it is?

Right. You cant take total lumens and divide by 525 to get the answer you want. Wish it was that simple. You need a lighting layout done for you to do it properly. What you CAN do, however, is poke around the GJ forum for folks who have a similar size garage as you and see what they have done. There's a sticky on the lighting forum that has a bunch of different layouts done. I bet there's one similar to yours on there. Have a look....
Good luck,
CD

 

[bczygan]

So let us get you close.

What are the length, width and height of the space, and the colors/ finishes? And how high will you mount the fixtures?

To me there are 2 main ways to light a garage/shop space.

One is if you are just parking cars in there with a workbench at the end. For that situation, you give a fairly low level of light, just enough to walk through the space. Then You put task lighting at the workbench so fine work can be done. I recommend 25FC actual minimum, for this.

Note that calculated and actual FC will differ quite a bit.

The other method is to put a high level of light throughout the space, so detail work can be done anywhere in the space. I recommend 50FC actual, at the work surface for this.

Give me the above info and maybe post some photos of the space and tell us what the uses and layout will be.

I'll run it through a calculator.

http://www.e-conolight.com/lightinglayouts/FlashIndoor.htm?InputOutputMode=XML&InputURL=FlashIndoor_Input.xml&OutputURL=SaveXML.php&PhotometricURL=PhotometricDB.php&InstanceKey=LightingAnalysts

Bill