Need some lighting layout advice

[bjcouche]

My shop is a 40’x64’x14’ pole building with open steel trusses. The walls and roof are covered with white metal. I believe I have settled on using 4’ LED ready T8 fixtures with LED bulbs. This seems to be a good value and would provide the least amount of glare. I also like that the bulbs are separate from the fixtures. I’m rejecting the lighting options with the led’s built into the fixture because inevitably the driver circuitry in them fails, and then you are stuck buying a different type of fixture because the original ones have been discontinued. With T8 LED replacements, the bulbs should be available for a long time.

My trusses are as shown in the pictures. I have 4 sections, clear spans between trusses. The center two sections have the trusses spaced 16’ apart. The end two sections have 15’ between the truss and end wall. My thought was to hang metal strut between and through the trusses as shown in the picture. The strut is the short green section for mock up, imagine it goes 16’ in either direction. I want the strut to go through the trusses because it get’s the lights above the bottom of the truss. My garage doors are high lifted to close to the bottom of the trusses.

This plan sets up the lights in 4 rows. The two rows closest the walls would be at about 15’ from the floor, and the inner two rows would be at 16-17’ from the floor. I’m spacing the rows fairly equally apart as shown in the drawing. I’ve used the Acuity Brands Visual Interior tool to get some idea of the amount of foot candles of illumination but have not yet been able to figure out how to use dialux evo. My drawing only shows part of the layout, scaled 1’ per square (squares didn't show up on the scan), roughly to scale.

The main question is, should I use 6 or 7, 4’ fixtures per half row? On the drawing I show three options, A, B and C.

Option A uses 7 fixtures spaced 4” apart with a 4” conduit between them, and a 10” space to the end wall. Note that the center fixture goes through the truss, which is 4” wide, so I don’t know if that will cause a shadow issue.

Option B uses 6 fixtures, spaced 16” apart on the center sections and 12” apart on the end sections with 6” space to the end wall. They are still mounted above the bottom of the truss, but none of the fixtures go through the truss.

Option C uses 7 fixtures with the fixtures mounted end to end with no spacing. One fixture goes through the truss. The spacing from the last fixture to the wall is 36”. There is also an 8” spacing between each half row to the truss, I could shorten that a couple inches by increasing the distance to the wall…

Thoughts? I'm looking for some thoughts and ideas to sway me to one of those options...
Brian

 

[Platonic Solid]

What's the ceiling pitch?
What's the primary purpose of the space?
Do you have a fc @ workplane target?

 

[bjcouche]

You'd think with all that text I would have remembered to include the important info...
The roof pitch is 4/12
The use of the space is mixed with some woodworking, and automotive. I won't be doing any auto body or paint work, I leave that to those more skilled in those trades...

I was looking at 70-90 fc just from what I've read on this forum. I've read through a large portion of the "best light fixture ever" and "light fixture layout collections" but there's bound to be stuff I've missed.

I have "old mans eyes" so more light is usually better, but glare is also an issue. The light in Walmart seems to bother me when I walk in, but I cannot place my finger on whether it's the intensity, color, or just walking into a brightly lit room from an overcast day outside... Either way I plan on buying a couple fixtures and bulbs of different temperatures to test them out before placing the big order for the entire shop.

Brian

 

[Platonic Solid]

The one downfall of most 4ft LED retrofits = no dimming. Dimming would permit you to go a little higher when you need it and lower if you experience glare. As for your Walmart experience, keep in mind it takes a few minutes for your eyes to fully adjust to significant luminance changes.

 

[cybrdyke]

I also like that the bulbs are separate from the fixtures. I’m rejecting the lighting options with the led’s built into the fixture because inevitably the driver circuitry in them fails, and then you are stuck buying a different type of fixture because the original ones have been discontinued. With T8 LED replacements, the bulbs should be available for a long time.

Re-think this theory.
First, Drivers in LED fixtures are replaceable, so if one dies, you wont need to buy a different type of fixture because the original ones have been discontinued. LED fixtures designs are far superior to tube designs and will easily outlast the tubes.
It's more likely that the T8 LED bulbs you will buy to replace the ones you install today wont be available and you'll have to buy different ones.

I wouldn't install LED tubes if I built a new shop. No way.
CD

 

[Platonic Solid]

You'll need roughly 270,000 lumens to hit the low 70s fc mark at 30" workplane. In other words - Approximately 50 2-Lamp 4ft strip lights populated with Qty.100 2640 lm bulbs. Not sure how many fixtures/bulbs you were thinking.

You'll need roughly 330,000 lumens to hit 90 fc @ workplane.

 

[bjcouche]

In my layout options above, I was trying to decide between 6 or 7, 2 bulb fixtures to have per 1/2 row (4 rows total). To multiply that out for the full shop, that would be 48 fixtures (96 bulbs) or 56 fixtures (112 bulbs). I was looking at the LG-4T8-22WBB-SM which is indeed 2640lm each. So 96 bulbs would be 254,400lm and 112 bulbs would be 296,800lm.

So it sounds like you are saying that 254,400lm would be around 70fc at 30". Compared to 296,800lm would be just under 90fc at 30" based on your numbers and my linear extrapolation guestimation.

That leads me to lean towards the 56 fixtures, with 112 bulbs, which would be option A or C in my drawing. Option A has the last fixture 10" from the end wall and option C has the last fixture 36" from the end wall. From a lighting aspect, is 36" too far or 10" too close?
Brian

 

[Platonic Solid]

I said 330,000 to hit 90fc, thus 300,000 will be right around 80fc.

The closer to the wall the larger the bright spot on the wall, but these just aren't that bright and at your mounting height it makes even less difference. Somewhere around 2ft to wall is fine.

 

[bjcouche]

Can I hear some reasons why I should NOT go the T8 LED light route as compared to the high bay light route? I'm trying to get more confident in my decision before I place the big order....
Some cons to the T8 LED light route that I can think of:

More fixtures: Not too much of a concern, as I'm doing the wiring and mounting cost is no different either way.

Not dimmable: I don't believe I need this anyway. I'm planning on having 2 or 4 switches so that I don't have to turn them all on if needed. If I wired them with 1 switch controlling every other fixture, I'd essentially have 2 levels of brightness....

Brightness: With 56 fixtures and 112 bulbs putting out 2640lm, that gives me 80fc. I'm assuming that should be enough for general auto repair and woodworking.... I guess I could do 5 rows of 14 instead of 4 rows of 14....

After reading most of the light fixture thread, I don't fully understand the reasoning that 4' T8 LED fixtures aren't recommended for higher ceilings. Is it just due to the higher number of bulbs / fixtures needed? This doesn't math out for me because when I look at pricing for high bay fixtures (with leds, fixtures and drivers as one piece) for the same 80fc, I end up at nearly double the cost for the high bay option.
Brian

 

[OneOfEm]

After reading most of the light fixture thread, I don't fully understand the reasoning that 4' T8 LED fixtures aren't recommended for higher ceilings. Is it just due to the higher number of bulbs / fixtures needed? This doesn't math out for me because when I look at pricing for high bay fixtures (with leds, fixtures and drivers as one piece) for the same 80fc, I end up at nearly double the cost for the high bay option.
Brian

Light falls off with distance from the light source. As fixture height increases, at a point, the highbay fixtures make sense.

 

[cybrdyke]

56 fixtures vs 15 fixtures.
100 points of failure vs 15 points of failure.
50,000 hours life vs 150,000 hours life
2200 watts vs 1900 watts
non-dimming vs dimming
open tubes vs modern look
socket aging vs no sockets

Good luck,
CD

 

[Platonic Solid]

I knew I'd regret posting crude lumen output figures. It's actually even worse than CD pointed out. There are more variables to take into consideration such as beam spread. The zonal lumen summary of a 120° beam spread 4ft lamp has 65.6% of its luminous output within the 120° beam spread. A linear high bay has 83.2% of its luminous output within its 120° beam spread. This means that the linear high bay is directing more of its output towards the ground where you need it and more of the 4ft bulbs output will end up on the walls where you don't need it.

A quick mock-up showed the following:
You actually need 72 4ft strip lights (144 bulbs) to hit 93 fc @ workplane.
vs
Qty.24 14400lm linear high bays = 94fc @ workplane.

If we just look at raw lumen output without taking beam spread into consideration, then the strip light wins:

4ft 5280 lumen strip light = approx $30 = 176lm/$
2ft 14410 lumen linear high bay = $91 = 158lm/$

Once beam spread is figured in it becomes a tie:

4ft strip light = $30 x 72 = $2,160
2ft high bay = $91 x 24 = $2,184

After power consumption the high bay wins:

4ft strip light = 44W x 72 = 3168W
2ft high bay = 110W x 24 = 2640W

If we were including installation cost, the high bay would win again.

 

[cybrdyke]

I knew I'd regret posting crude lumen output figures.

I was wonderin' what you were thinkin'.....

 

[bjcouche]

Thanks Platonic, this is the kind of information that I was looking for.
You said that I would need 72 4ft strip lights (144 bulbs) to hit 93 fc @ workplane. That makes another drawback, to the strip lights. In order to get 70 strip lights to fit I will have to increase my number of rows from 4 to 5, and that adds an appreciable amount of fixture hanging material cost.

Add to the confusion that I plan on walling off a portion at on end of the shop and thus have 2 stories in that location, so the height at that area won't be 16', more like 8'....

Thus my conclusion is that I must first determine exactly what dimensions I'm walling off to create the mezzanine / woodshop area. Then I should figure out how to use the Dialux evo program, and consider a combination of high bays and strip lights based on the height / shop layout. I was originally thinking that I could just do the strip lights, and be done with the lighting, but now that you've educated me more it looks like I need to step back, add in all the variables, and recalculate.

Slightly off topic, do you know what type of fixture Walmart is using? They look like they are single bulb, T5 or T8 LED reflector fixtures with the rows spaced 10' apart. Definitely looks like the bulb is replaceable separate from the fixture.
Brian

 

[cybrdyke]

do you know what type of fixture Walmart is using? They look like they are single bulb, T5 or T8 LED reflector fixtures with the rows spaced 10' apart. Definitely looks like the bulb is replaceable separate from the fixture.
Brian

Walmarts are lit with a combination of sky lights and fluorescent T8 strips. The T8's are dimmable and are controlled by sensors on the ceiling that measure the amount of daylight coming in. The control system dims and brightens the lights all day without anyone even noticing it. They are upgrading stores to LED as they see fit and any new construction has controllable LED.
CD