Lighting

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vptran

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Happy Holidays everyone,

I am currently learning about lighting, and am having a little trouble understanding it.

I have to design lighting for a 200 ft. wide, 120 ft. deep, and 20 ft. high building. The building requires minimum 40 footcandles of light. How many Metal Halide low bay lights will I need? And what proper spacing of light fixtures will i need in order to provide evenly dispersed lighting.

Here is my calculation:

Footcandles = Maintenance Factor X lumens X C.U / (Area in square ft)
Footcandles = 40
Maintenance factor = 0.8 for ceiling of office lighting
C.U. = 0.35
Area = 200 x 120 = 24000 ft squared

Substituting, Lumens = 3428571.43

Using LSI Lighting systems HID Lamp table: I use ANSI#M59 Metal Halide, and it's 458 Watts/light

Now I am stuck because I don't know how to find the number of lighting fixture and how much I need to space these fixtures.

If anyone can help and steer me in the right direction, it would greatly be appreciated.

Thanks
 
You need to fully understand the equations and use units in every calculation to help you understand it.

40 FC per square foot x 24000 square ft = 960,000 FC required on the floor.

You are using a maintenance factor of 0.8 and a coefficient of utilization of 0.35, so you can calculate the total lumens required from the bulbs:

960,000 FC/(0.8 x 0.35) = 3,428,571 lumens required from the bulbs.

Now you need to get lumens per light, which are not given in your post. I looked up the M59 and they run 36,000 to 40,000 lumens per bulb (initial lumens). Since you are using a maintenance factor and coefficient of utilization, you can use the initial lumens. Let's use 38,000 lumens.

NOTE: You need to find something in your input data that converts those Watts to Lumens for your problem.

Now let's calculate how many lamps you need:

(Lumens required at bulbs) / (lumens per bulb) = 3428571 lumens/38,000 lumens per bulb = 90.2 (say 90 bulbs).

Area per lamp = 24,000 sq ft/90 lamps = 267 square ft per lamp.

The square root of 267 is about 16.3, so you will need about a 16 ft square pattern, or equivalent slightly rectangular pattern, or a staggered pattern.

You can arrange 91 lamps in 7 rows across the 120 ft dimension, with 13 lamps in a row for the 200 ft dimension. You could get fancy and make a hexagonal pattern but that is probably like milking mice.

If you put your own lumens into the formulas, you can plug in the numbers and do your own calculations.
 
Thanks for the response,

So there is a total of 91 light fixture (7 x 13), each light fixture is spaced approx. 16 feet apart. 7 light fixtures goes across the 120 feet wall, and 13 light fixture goes across the 200 feet wall?

Is this correct Bob...

Thanks for the clarification.
 
Bob NH said:
You are using a maintenance factor of 0.8 and a coefficient of utilization of 0.35, . . .
Click to expand...
Bob, would you mind explaining those two figures, please? What they mean and how they're derived.
 
thats a big darn grow room !!can you say hydroponic ??

don't do it or you'll be rooming with bubba for a looong time
 
call your supply house they will send a lighting rep to the work site and spec out the proper amount of lights your'll need. he should give you a scetch of his layout and go over the way lighting is spec out. that could be the easy way to to have it done.
 
vptran

vptran

Just an FYI:

I just took my trusty Minolta T-1 illuminance meter and measured the foot-candles of my warehouse. (60' wide x 100' long, 20' high ceiling -- (7)-8' wide double fluorescents spaced 10' apart,) placing the unit on the ground it read 21.4 foot-candles. I could not imagine the warehouse being any brighter.. I would have to hand out shades:smile:
 
LarryFine said:
Bob, would you mind explaining those two figures, please? What they mean and how they're derived.
Click to expand...
I was using the factors provided by the original poster. I made no attempt to evaluate or justify the figures. You can find some info at this link.
http://ergo.human.cornell.edu/studentdownloads/DEA350pdfs/lightdesign.pdf

Maintenance factor is the allowance for loss of light during the usable life of the lamp/bulb. The bulb manufacturer usually provides data on degradation during life of the bulb. The architect or designer decides what factor to allow for degradation; when do you want to change the bulbs to maintain the specified lighting values.

Coefficient of utilization is the factor, usually supplied by the fixture manufacturer, that represents what fraction of lumens produced by the bulb actually gets to the surface where the light is desired.

VPTRAN: You are correct on the arrangement of the lights. Be aware that I was NOT designing your lighting system. I was taking you through the arithmetic of the problem that you posed.
 
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edamico11 said:
Just an FYI:

I just took my trusty Minolta T-1 illuminance meter and measured the foot-candles of my warehouse. (60' wide x 100' long, 20' high ceiling -- (7)-8' wide double fluorescents spaced 10' apart,) placing the unit on the ground it read 21.4 foot-candles. I could not imagine the warehouse being any brighter.. I would have to hand out shades:smile:
Click to expand...

The building type and work being will determine the amount of lighting required. As you can imagine a typical warehouse will require less lighting than a manufacturing/assembly plant. A manufacturing/assembly plant thats working with really small objects will require even more lighting.
 
For God sake new ee it's new years.....

For God sake new ee it's new years.....

The building type and work being will determine the amount of lighting required. As you can imagine a typical warehouse will require less lighting than a manufacturing/assembly plant. A manufacturing/assembly plant thats working with really small objects will require even more lighting.
Click to expand...

I must agree,, however in my situation we have specialized area's for sensitive work. It saves money on electric and gives people a place to hide:grin: .. Anyway I guess that is where the lighting design comes in.
 
Are there going to be shelving in this warehouse? If there will be storage and pick parts, you also need to consider the vertical footcandles so you can read the labels on the boxes better. Then aisle lighter fixture would be a good recommendation. 40 Fc does seem bright for a warehouse. you may also consider some type of dual switching arrangement to turn on half of the fixtures and still be able to work in the area. Especially important for California and Florida energy codes.
 
Imagine the lighting plane being vertically oriented instead of horizontal. I create a calculation plane in the Visual software to obtain the lighting levels. I do not have the patience to perform a manual calculation. Anyway, vertical footcandles illuminate the walls and aisles. Ever walk into a corridoor or room and it had enough light to read, but felt like a cave? That is the effect of not enough vertical footcandles. One of the biggest mistakes by people is using parabolic fixtures for an office area for a corridoor. Then the top half of the walls are dark and it feels unpleasant.

Look at the photmetric web diagram for different MH high bay fixtures from any manufacturer, you will see the difference from a typical High-bay and a Aisle lighter.
 
that is,,

that is,,

a very interesting observation,, It seems to be like the difference between focusing light, and "flooding" light. I will have to keep this in mind:smile: .
 
Think more of the cut-off angle of the light.

Also Aisle lighters have special optics to control the light to light up the shelves. It's pretty interesting how they do it.

Glad to help.
 
Bob,

This was just an example problem regarding calculating lumens and the amount of light fixture one would need per the allowed minimum footcandles. I am not designing this at all...just needed some clarification on the math.

Thanks for the inputs.
 
vptran said:
If anyone can help and steer me in the right direction, it would greatly be appreciated.
Click to expand...

I think you're doing this the hard way. I suggest you go to http://www.lithonia.com/Software/Lightware7/Visual/Default.asp and download the basic version of Visual. You'll need photometric files for the exact fixtures you want to use, but these are available from the manufacturer's web site for most fixtures.

The number of fixtures required is dependant on the optics of the fixture, not just on the lumens per lamp. That's the advantage of using a program for this -- you can calculate lighting levels by hand and take hours, but the computer will do the calcs in seconds. If you specify lighting level, room size, and the exact fixture Visual will calculate the number of fixtures required. For a room like this I will generally try several different fixtures, different lamp wattages, different spacings, etc., to optimize the layout.

Be sure to set the work plane height correctly (it could be 0", 30", or 36" depending on what they do in the space), and I'd recommend a light loss factor of 0.72 rather than 0.8 if you use metal halide.

As others have pointed out, if this is a warehouse with high stack shelving you need to take an entirely different approach than if this is open space. Also, you might want to consider using fluorescent instead of metal halide, especially with a 20' height. Look for "fluorescent high bay" or "aisle lighter" fixtures. Fluorescent lets you split the lamps in each fixture into groups so you can lower the lighting level to meet IECC requirements, and you don't have to take special measures for emergency lights due to the strike time for metal halide lamps.

Martin
 
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