Woodlot, I posted all that stuff so folks could decide what they wanted and design carefully for their needs. That said, I designed my system using
this free software,
which requires a download and running the program which allows you to specify how many lights you will use, height they are mounted, type of bulbs, length and wattage, etc...
About 150 lumens at work table height is ideal from my perspective... that's what my design point was. I'm extremely happy with it.
Without using that software, my gut feel for your situation is as follows:
I'd use bulbs with the largest Kelvin color number you can get. The higher the number, the easier it is to see stuff.... in houses, people use lower numbers to set mood, show off skin tones better, etc.. but in a shop I wanted the light to be as white/bright as possible, thus selected 6500K bulbs. Get the maximum lumens per watt as well.
The best mix of all this for me was the
Plilips Homelight Deluxe . If you use cooler, smaller Kelvin bulbs, then it is possible you may need to increase the number of fixtures to get more visible light.
To me, a T8 bulb is a much better selection that T12, which many of the 8 foot fixtures are...lumens per watt are usually better with T8 than T12.
I used 4 foot fixtures rather than 8 foot. My reasoning was that I could spread out 4 footers more an avoid shadows better than with 8 footers. It was the right decision for me. Two four footers were cheaper than 1 8 footer as well by a hair.
I used 25 4 foot double tube fixtures for 2400 sq feet.
You have 1620 sq feet, thus about .67X25= 17 such fixtures for you, if your ceiling height were same as me....but since it's 10', you need less.
I agree, 3 rows could do you fine. Maybe 3 rows of 5 = 15 fixtures. However, I did 5 rows for a 40' span as shown in the photo and am convinced that was the way for me to go. With 4' fixtures, there is a lot of flexibility in placement that you don't get with 8 footers. You can see that I concentrated the fixtures a little more over work areas and a little less over non intensive work areas. You may wish to do the same. I'd get a bunch of 2X4's or something and lay them down on the floor of the shop, 1 for each fixture placement on the ceiling.... eyeball whether you'd rather have 8' or 4' fixtures, and how many.
If you use anywhere between 15 and 18 4' fixtures, I KNOW that you'll have a bright work shop. Actually, the numan eye (excepting for macular degeneration/cataracts) really adjusts amazingly to light and you could possibly be happy with as few as 10 fixtures... without running the software to calculate the effect of ceiling height and fixture placement, hard to tell.
I have my lights on 3 switches, thinking that I'd cut off the bank(s) that I didn't need when working in the shop. I've discovered that I move all around the shop at present, thus leave all the lights on when I'm in there. Maybe I didn't need all the switches, but am glad I got them. Particularly since the center row of lights has a switch at EACH entry door, allowing me to cut it on/off easily. This allows me to get sufficient light to get a tool quickly or get over to the rest of the switches without killing myself.
I discovered it's EASY to spend A LOT on fixtures, I studied hard and settled on Lithonia and the cheapest ones I could find...Note that I got them for less than $18 each (below their cost) at Home Depot... and then selected the brightest refelector within that group. A reflector is extremely important to focus the light down... who needs it on the ceiling?
I got my wiring from the local metal recycling place. I discovered that I can get complete rolls of wire there for about 1/3 the cost of new at Home Depot... and the plastic is still on the roll... For some reson, it shows up there and it works for me. You use lots of wire... particularly if you install multiple switches at multiple doors.
jmc, I do not recall ever seeing mention of instant on lights drawing current when off... I don't believe it.... I think that the instant on is a feature of a particular kind of ballast. I'm sure I would have noticed a comment to that effect during my research, which included a focus on energy efficiency.
If somebody has facts to the contrary, please post a believeable web site with that information.
That's it, guys, hope it helps!
. The fixtures I was considering did not have a reflector, I'm unsure if they take a T8 or not, and I had no idea what kind of tube to look for. I'm so glad I asked.