Lighting-Rules of Thumb?

[dhubbard422]

Hello,

I thought I'd start this thread to see if I can get the lighting experts to chime in with thoughts regarding lighting/illumination guidelines for all of us non-experts.

There are so many threads that touch on this subject. I have found Platonic Solid's layouts very helpful. Other's have also posted various "rules of thumb", which are also helpful, BUT I wonder if there are more! Here are some that I've found.

Recommended Lighting Levels: Is there a better guide than this?
http://www.engineeringtoolbox.com/light-level-rooms-d_708.html

Schrodingers Cat posted - 60% rule of thumb (for "effective" lumens)
http://www.garagejournal.com/forum/showpost.php?p=646892&postcount=44

But, I wonder if that 60% RoT could be further refined based on ceiling height?

I found several layouts (created by Platonic Solid) for shops with 12' ceilings (the ceiling in my workshop is 12'...). His layout examples typically seemed to aim for (roughly) 80 - 90 "effective" lumens on the work surface and the difference between claimed bulb output and "effective" lumens on the work surface was roughly 60% (in his examples for spaces with 12' ceilings).

I've also seen a RoT for light spacing (between rows of flourescent lights) that was something like - not further apart than the distance from ceiling to floor (or was it ceiling to work surface?)

But what about a RoT for distance from workbench? For example, I want really good light on my workbenches, but does this mean that I need a row of lights right over my workbench? Centered over the workbench? Directly above the front edge of the workbench? Within a couple of feet of the front edge? Or?

Many of Platonic Solid's Layouts, which generally seem to use 4' tube style lights, often placed several lights between the primary rows at 90 degrees to the rows. Usually at the (end) walls between the ends of rows of lights. I'm guessing that a RoT might be that workbenches are often/usually against walls so put lights there. But, I also wondered if helps produce a more consistent, even illumination if some bulbs are place between the rows where these bulbs are rotated 90 degrees to the primary rows?

Are there RoT for materials? White metal ceilings vs white painted drywall? White walls vs wood walls? Racedeck vs polished concrete? What impact would materials have on the 60% RoT?

What about aging and eyes? I've started my 6th decade and well... I need a lot more light now (for detail work) than I used to and I doubt it's gonna' get any better! Any guidelines?

Thanks in advance! I hope that this thread can generate some good discussion!

 

[kd3pc]

Hello,




What about aging and eyes? I've started my 6th decade and well... I need a lot more light now (for detail work) than I used to and I doubt it's gonna' get any better! Any guidelines?

Thanks in advance! I hope that this thread can generate some good discussion!

this is the only one I can help with, as I too, am 60...

The first part of the post, the answer is - it depends....so much on what you are doing and is there a reason to need that much, or that little light.

As to the quoted part, I parted with $25 and purchased a Petzl headlamp that has two levels of light that are mounted on a 3 notch base. It has solved all but the need for magnified light for fine work. For the detail work, surface mount ICs and ham radio kits and repairs, I work with an older ring lit, fluorescent magnifier.

Best of luck, and I hope to learn more about what the experts have to say on your post.

 

[dhubbard422]

^^^^^
Yes, a headlamp can help tremendously! I have several laying around. I haven't yet tried a lighted magnifier... but, I expect that one is in my future.

I also agree that "it depends..." is all too true. My needs will vary greatly, from automotive and motorcycle repair/assembly, machining and fabrication. I am trying to avoid turning this into a thread on designing my lighting needs, but for this that are curious, I posted my lighting plan in my build thread (post 47)

 

[cybrdyke]

I'm in the business. There are no rules of thumb that I use. I dont know anyone else in the business that does, either. Lighting is a very complicated science. The people in the business are professional engineers and designers.
All the information that a lighting professional needs is readily available and in a form that we can easily use. The things we need to know about the spaces are dimensions, reflectances, surfaces, and of course, what the space will be used for.
Every legitmate lighting manufacturer provides loads of information about their product. We have photometric files and lots of 3rd party testing results. All this info is dropped into some pretty extensive and pricey computer software.
The target lighting levels are determined by the Illuminating Engineering Society. Their handbook is pretty close to 6" thick.
There's not much left to guess about. It might seem pretty technical, but like anything else, it becomes pretty routine once you do it enough.

 

[dhubbard422]

^^^
cybrdyke, thanks for stopping by...

 

[dhubbard422]

I found a couple of tools for lighting "layout". GE has a calculator that they call the Lighting Layout Estimator, it will estimate the number of fixtures needed to light an area to a specified light level.

GE Lighting Layout Estimator

Interestingly, there are only three primary variables:

• Desired illumination (in foot-candles)
• Balast Factor
• Coefficient of Utilization (CU)

GE defines (CU) as:
fraction of light from the lamp that finds its way to the work plane. It is a critical number in lighting layout calculations.

A default value of 0.60 is used in this estimator, which is appropriate for most rooms with fairly bright walls and furnishings. More efficient fixtures will have higher CU's. Rooms with dark walls and furnishings will have lower CU's, e.g .40 or .50. Indirect lighting may have CU's in the 0.30 to 0.50 range. Consult fixture spec sheets or manufacturer to obtain

So, if the rule of thumb recommended by GE works for you, simply use the calculator (link above) or just use the following formula to determine how many lumens might put you in the ballpark:
1/CU * desired # of lumens per sq ft * size of your shop in sq ft = total lumens needed to realize the desired light level
e.g. for my shop, this would be: 1/0.6*100*1080=180000 lumens

The advantage of using GE's calculator is that given info about the lamps you plan to use, it will also calculate the number of lamps

 

[cybrdyke]

You're way short. Way...
CD

 

[dhubbard422]

I also found another simple tool: "FlashIndoor" by Lighting Analysts. It appears that they (Lighting Analysts) make a simple flash-based (web) tool that can be embedded by lighting manufacturers in a web page. However, it has quite a few more additional inputs than the GE calculator, including spec sheets for various lights, room geometry and multiple reflectance coefficients to estimate CU.

The link to FlashIndoor (demo/promo page) is:
http://www.agi32.com/index.php?id=131

Click on the "Flash Indoor" logo above the prompt "Test Drive Flash Indoor Now!" and it'll launch the tool in a new window.

Since this tool is designed to be embedded lighting manufacturer, it might be confusing to identify an approximation of an appropriate photometric file. I was looking for standard 2 bulb T8 fixture and the 2nd file (in the Luminaire tab of this demo) is close enough for me...

The Geometry tab will let you input the size of your workshop. The distance from the light source to the work surface will also impact the "Reflectance Coefficients" (CU). If you want to play with the ceiling, wall and floor reflectance, you may want to look at this page of Material's Coefficients. It's pretty amazing how low the reflectance coefficients are for medium to dark painted surfaces are...

Anyway, I though this tool was interesting. It, like the GE calculator, defaulted to a CU that was roughly 0.6 for my 12' ceiling with roughly 9' from the light source to the work surface. But if you know your finishes, you can estimate their impacts by plugging in various values for those coefficients.

 

[dhubbard422]

You're way short. Way...
CD

Not the first time I've been told that!

But, seriously - why do you say that?

I analyzed 3 similar sized layouts that were generously published by Platonix Solid and these numbers are higher than those in the similar sized layout designs he recommended. So, it seems you also disagree with his layouts as well as the GE calculator. This (disagreement) is fine. But why?

I understand that the formula I enumerated is simple. It is a rough "rule of thumb", a starting point. Lamps deteriorate. Fixtures deteriorate. Eyes age. These numbers don't incorporate coefficients for those issues. And reflectance of materials is really hard to model... and very "approximate"...

Is it that 100 lumens per sq foot on the work surface is inadequate illumination? Or is it something else?

Thanks,
Don

 

[cybrdyke]

A few issues with your figures.
First, lets talk about semantics. It'll help unconfuse you, moving forward. The target level you are seeking is foot-candles, not lumens per square foot. Yes, I realize that there's a similarity, but there's also a huge difference (it's technical). So, let's talk in foot-candles. How did you come to choose 100 fc as your target?

You left the ballast factor at 1.0. The ballast factor for a normal ballast is .88. You need to change that in your calculations. This also, then changes your lamp lumens from 2850 to (2850 x .88) 2500, a 12% reduction.
You are also calculating based on the lamp lumens from Day 1. The moment you start to run those lamps, they are fading. It's typical to design to "mean lumens", which is the level that the lamps will be after they're 40% of life. Doing this will give you the appropriate amount of light for much longer during the lamp's life. Yes, on Day 1, it will be bright! Your 32w T8 lamps have a mean lumen of 2450. Multiply that by .88 ballast factor and you're at 2156 lumens per lamp.
Now, none of your lumens have left the fixture yet. Depending on the fixture that you choose, only about 70% of them will make it out. This is one factor in to the CU. When you choose a fixture, that manufacturer can give you this number exactly. Your ceiling may be 80% reflective, but your finished wooden walls will likely fall short of the normal 50% reflectance. Your shiney floor (it's nice!) will only add a couple extra points. Plus, most fixture photometry info is based around an assumed ceiling height or 8' to 10'. And you're at 12'.
So....you're way short. Way.
CD

 

[bczygan]

I just like it plenty bright, with no shadows anywhere and 6000K color.

Bill

 

[dhubbard422]

A few issues with your figures.
First, lets talk about semantics. It'll help unconfuse you, moving forward. The target level you are seeking is foot-candles, not lumens per square foot. Yes, I realize that there's a similarity, but there's also a huge difference (it's technical). So, let's talk in foot-candles. How did you come to choose 100 fc as your target?
CD

You made many points, most I am sure are good. If you would, help me understand the first paragraph.

Every definition of Foot Candle that I can find states: Foot Candles = Lumens per square foot (edit: to be precise, I should have written: 1 Ft Candle = 1 Lumen per sq ft). I should be able to handle technical and I am curious.

As I noted in the first post, engineering toolbox provides a chart of recommended light levels; it seems to be widely quoted on the web; I asked if there was a better guideline.
http://www.engineeringtoolbox.com/light-level-rooms-d_708.html

I also found this autodesk workshop tutorial (it also defines Ft Candles and makes recommendations for lighting levels for a variety of tasks)
http://sustainabilityworkshop.autodesk.com/buildings/measuring-light-levels

The WIDE range of target illumination for common workshop tasks is in itself a huge rule of thumb.
- Is 50 foot candles adequate? "moderate demand for visual acuity, e.g. computer work, reading & writing".
- What about 75? "good visual acuity, e.g. drawing offices, general electronics work"
- 100? "superior visual acuity, e.g. detailed electronics assembly, drafting, cabinet making"
- 150 - 200? "maximum visual acuity, e.g. hand tailoring, precision assembly, detailed drafting, assembly of minute mechanisms"

I expect that I will perform tasks that have lighting needs that range from moderate to maximum. I also expect that I will place task lighting here and there as needed and/or use an illuminated magnifier...

What do you recommend for an "average" value for workshop illumination? Do you recommend a better guideline for determining an appropriate target illumination level?

Thanks,
Don

 

[dhubbard422]

I just like it plenty bright, with no shadows anywhere and 6000K color.

Bill

Bill,

Bright is good! Dim with lots of shadows is challenging...

The brightest shop I've seen here is RAY916MN's Pallet Racked Motorcycle Garage, but even it has shadows here and there.

Don

 

[fteufert]

I bought the LED 48" lights from Sams club (lights of America)

They are bright and cheap to run.

In my 20x20 garage, the two I have are brighter than the other 6 fluorescent 48" fixtures.

As for a layout, put one directly over where you do the most work, and have other fill in the remaining space.

Lights are cheap, too many can't be enough sine at 50, I can't see much without bright lights!

 

[cybrdyke]

You made many points, most I am sure are good. If you would, help me understand the first paragraph.

Sure, I'll try.
Watch this video:

When using the term "lumens per square foot", people think that this means that you can take the amount of lumens delivered by your light source (luminous flux), and divide that by the square footage of the space. It absolutely does not mean that. On Garage Journal, in particular, this definiton has been so profoundly mis-used, that it's staggering. So, in order to avoid that confusion, the industry uses the term "foot-candles".
Illuminance on a target can only be measured with a light meter in foot-candles. It is the amount of light falling on a surface. The lumens bouncing around in a space, that all end up at your target, all contribute to illuminance. The amount lumens, from all directions and sources, including daylight, end up at a 1 square foot target = illuminance. And there are so many environmental and electrical factors that need to be accounted for that affect illuminance. This is where the lighting software starts to come in. You've kinda got your toe in the water with this, so I hope you keep playing with it.

If you plug the corrected figures that I gave you back into the GE calculator, you will see that it comes up to about 239,000 lumens, not 180,000.

As I noted in the first post, engineering toolbox provides a chart of recommended light levels; it seems to be widely quoted on the web; I asked if there was a better guideline.
http://www.engineeringtoolbox.com/light-level-rooms-d_708.html

I also found this autodesk workshop tutorial (it also defines Ft Candles and makes recommendations for lighting levels for a variety of tasks)
http://sustainabilityworkshop.autodesk.com/buildings/measuring-light-levels

I give Engineering Toolbox a "C" for effort. The formulas may be correct, but there is no useful information there to help you determine what to do with the data.

The WIDE range of target illumination for common workshop tasks is in itself a huge rule of thumb.
- Is 50 foot candles adequate? "moderate demand for visual acuity, e.g. computer work, reading & writing".
- What about 75? "good visual acuity, e.g. drawing offices, general electronics work"
- 100? "superior visual acuity, e.g. detailed electronics assembly, drafting, cabinet making"
- 150 - 200? "maximum visual acuity, e.g. hand tailoring, precision assembly, detailed drafting, assembly of minute mechanisms"

I expect that I will perform tasks that have lighting needs that range from moderate to maximum. I also expect that I will place task lighting here and there as needed and/or use an illuminated magnifier...

What do you recommend for an "average" value for workshop illumination? Do you recommend a better guideline for determining an appropriate target illumination level?

Thanks,
Don

Yep, the illuminance levels are all over the map. No, I dont have an "average" that I can give to you, but if you would like a few personal suggestions, I'm happy to offer them.
A good place for you to start would be to select a fixture that you like. All of the manufacturers data will be there and you can start to put that info into the lighting software and it will do the work for you.

 

[dhubbard422]

CD,

I can (mostly) understand your preference to use the term Ft Candle, but it seems helpful (to me anyway) to use the same units that characterize the lamps... Anyway, I started this thread in order to *try* to see if there weren't some ballpark multipliers that can help me (and other GJ'ers) to understand how much (more) light is really needed to realize a specific illumination goal.

Unfortunately, as discussed, I don't even know what my desired target lighting level, or goal, should be! Suggestions are welcome! "Superior" visual acuity has a nice ring to it, but... is that just right or too little? I doubt it is too much. But, the range from "Moderate" to "Maximum" is pretty large, maybe something on the order of 4x.

So, in order to better understand your claim that my ballpark estimations were significantly low, I did a little (more) reading on light losses. I haven't looked too carefully at fixtures, but I used a BF of 1, because I haven't made any fixture or ballast decisions and because there is a pretty big difference between low and high output ballasts (> 20%, I think...) I also looked at depreciation factors today. I had previously seen data that indicated a 0.9 correction factor for output at mean lamp life. Using 0.88 * 0.9 gets me close to your numbers, i.e. 20% more light needed. But I also found a text that had curves on dirt - dirty luminaires and dirty surfaces and I was surprised at the wide range of correction factors that could be chosen depending on just how dirty fixtures and the environment is... it seems that even a reasonably clean shop might need 15% more light (0.9 * 0.95) to accommodate for dirt. So, it appears that a high output ballast could compensate for these recoverable light loss factors or I'm roughly 35% "short" given low output ballasts AND dirt...

I also found a paper: "Light and the Aging Eye" that suggests Seniors might need 4 times the amount of light (in W/sq ft) as a young person!

So while my shop might need a third more light fixtures/lamps to compensate for various correction factors associated with typical lighting losses, this is relatively minor compared to the large unknowns that are associated with setting goals for the desired target lighting level...


Coefficients used for my revised worksheet:
Non recoverable factors 0.53
CU: Coefficient of utilization 0.6
BF: Balast factor 0.88

Recoverable factors RF = LLD x LDD x RSDD 0.77
LLD: Lamp luminaire depreciation 0.90
LDD: Luminaire dirt depreciation 0.90
RSDD: Room surface dirt depreciation 0.95

LLF: Light loss factors 0.41
"Rule of Thumb" multiplier ( 1/LLF) 2.46

Sq footage 1080
Desired average Ft candles 100
Lumens require for desired average 265,816

Lumens per lamp 2850
# lamps 93
# fixtures 46

Don

 

[dhubbard422]

I finally have lights in my shop. And as you can read above, my lighting plans for this shop were all over the map! Specifically, how many lights do I need to buy and how should they be arranged to create a mostly uniformly bright workspace?

I went with the James 18w LED bulbs and Maxlight fixtures as recommended on the Best Light Fixture thread. There are (44) 2-bulb fixtures in the main area of the shop and there will be (4) 2-bulb fixtures in the closet.

I was aiming for an illumination average of at least 120 lm/sq ft or 1290 LUX. The plan below far exceeded that goal with a measured average LUX of about 1800.

I thought I'd share the plan and the measured LUX values for those that are planning/wrestling with their own lighting needs. Perhaps this will help you in your planning.

I want to call out a special Thanks! to PlatonicSolid for generously sharing his recommendations and suggested layouts.

Plan - Measured:

Hand drawn heat map:

Obligatory shop pic:

Note the specular highlights in the floor!

Hope this helps,
Don

 

[EOC_Jason]

To me the simple rule is you can never have enough light.

Long florescent lights will tend to be directional, in that the best light is radiated out along the long length. Step a few feet past the short end and it feels a lot dimmer. So plan direction based on where and what you are going to work on.

I also have one centered right above my workbench, this was actually the first one I installed in my garage.

Finally, there will always be times when you need extra light, either via a flashlight, clamp-light, or even a cheap desk lamp. I've also seen people drop down a florescent light on chains right above a machine for extra light. The finer the detail, the more light you want.

 

[dhubbard422]

^^^
Hard to argue with that simple rule.

Just realized that I did not include the workbench layer in these pics... the 3 rows of lights adjacent to and parallel to the side and end walls are located above workbenches. Without these lights, the workbenches would be "in the dark".

 

[Radix2]

CD,

I can (mostly) understand your preference to use the term Ft Candle, but it seems helpful (to me anyway) to use the same units that characterize the lamps... Anyway, I started this thread in order to *try* to see if there weren't some ballpark multipliers that can help me (and other GJ'ers) to understand how much (more) light is really needed to realize a specific illumination goal.

Unfortunately, as discussed, I don't even know what my desired target lighting level, or goal, should be! Suggestions are welcome! "Superior" visual acuity has a nice ring to it, but... is that just right or too little? I doubt it is too much. But, the range from "Moderate" to "Maximum" is pretty large, maybe something on the order of 4x.

So, in order to better understand your claim that my ballpark estimations were significantly low, I did a little (more) reading on light losses. I haven't looked too carefully at fixtures, but I used a BF of 1, because I haven't made any fixture or ballast decisions and because there is a pretty big difference between low and high output ballasts (> 20%, I think...) I also looked at depreciation factors today. I had previously seen data that indicated a 0.9 correction factor for output at mean lamp life. Using 0.88 * 0.9 gets me close to your numbers, i.e. 20% more light needed. But I also found a text that had curves on dirt - dirty luminaires and dirty surfaces and I was surprised at the wide range of correction factors that could be chosen depending on just how dirty fixtures and the environment is... it seems that even a reasonably clean shop might need 15% more light (0.9 * 0.95) to accommodate for dirt. So, it appears that a high output ballast could compensate for these recoverable light loss factors or I'm roughly 35% "short" given low output ballasts AND dirt...

I also found a paper: "Light and the Aging Eye" that suggests Seniors might need 4 times the amount of light (in W/sq ft) as a young person!

So while my shop might need a third more light fixtures/lamps to compensate for various correction factors associated with typical lighting losses, this is relatively minor compared to the large unknowns that are associated with setting goals for the desired target lighting level...


Coefficients used for my revised worksheet:
Non recoverable factors 0.53
CU: Coefficient of utilization 0.6
BF: Balast factor 0.88

Recoverable factors RF = LLD x LDD x RSDD 0.77
LLD: Lamp luminaire depreciation 0.90
LDD: Luminaire dirt depreciation 0.90
RSDD: Room surface dirt depreciation 0.95

LLF: Light loss factors 0.41
"Rule of Thumb" multiplier ( 1/LLF) 2.46

Sq footage 1080
Desired average Ft candles 100
Lumens require for desired average 265,816

Lumens per lamp 2850
# lamps 93
# fixtures 46

Don

Don,I think you are going about this the wrong way with these approximations and confusions with fluorescent bulbs and tech.


If you want a simple tool, use the one from Lithonia/acuity brands - enter your room size, walls, and try out various specific fixtures - this uses actual photometric files which remove all the ballast and reflector issues. You can as well use LED fixtures. If you are not using lithonia products, you can use .ies files from others or find a close match at lithonia.

http://www.visual-3d.com/tools/interior/

If you are more computer savvy and want a challenge, Dialux is good software to model to a high detail level.

And I think designing for 100fc at the work plane is a good rule of thumb for us older guys...or soon to be... because no matter what an expert may say, it is all the perception of the user in the end and you gotta start somewhere.