I have a 24'x24' garage with the back half having rafters at 8' off the floor. I currently have 3 4' 2 bulb florescent lights and 2 8' 2 bulb florescent lights. The ballast is shot on the 4' lights and the 8' lights are just too low and constantly get bumped (also had a 3rd one that caught fire last year) so I would like to replace them all with standard like sockets and compact cfl bulbs (probably 75 or 100 watt equivalent). Is 6-7 enough? I would prefer a little more light than I have now.
Switching to compact florescent lights, how many?
- Thread starter RustyGoat
- Start date
coralnut
Banned
Here's some fast math:
Part One: Lumens You Have
You have 16 feet of LFL lamps in your 8-foot/2-lamp fixture. You have 24 feet of LFL lamps in your three 4-foot/2-lamp fixtures, for a total of 40 feet of LFL lamps. Assuming that you buy premium lamps and operate them at a standard ballast factor of 1.0, a premium 4-foot F32T8 lamp will produce about 3,000 initial lumens, or 750 initial lumens/linear foot. Your 40 linear feet of lamps should put out about 40x750=30,000 initial lumens.
Part Two: Lamps You Need
Doing the second half of the math, you need enough CFL to produce the equivalent of 30,000 initial lumens. The packaging says that a typical "100W equivalent" CFL puts out 1500 initial lumens. Then you're going to need 30,000/1500 = 20 CFL bulbs to produce equivalent light output, when they are new.
Needing 20 CFL bulbs creates some logistical problems.
The first is that CFL bulbs don't retain their light output as well as linear fluroescent bulbs do. A typical CFL bulb may have it's output drop such that it's "mean lumens" rating (defined as the light output at 40% of it's rated life span) is only about 50% of the light output during it's first 100 hours of life. In other words, CFL don't preserve their light output very well, and they have a rapid fall-off in light output to about 50%.
Compare that to a standard T8 lamp which has > 80% lumen retention, or a T5 lamp that has > 95% lumen retention and you'll see that CFL bulbs are a really BAD way to light a room. They look fine when they're new, but as the bulbs age the room becomes dark and you need to deploy more bulbs to maintain the same light output. That means that if you needed 20 CFL bulbs to meet your lighting requirement according to the "initial lumens" rating, you'll probably need 40 bulbs to produce the same mean lumens over their entire rated life. 20 or 40 bulbs is an absolutely HUGE number. This is why you don't see any commercial facilities using CFL for lighting. They're always using LFL, HID or LED.
Another problem is that because CFL are not ballasted, they have a very poor power factor. They draw LOTS of current in relation to the light output they generate. This limits how many bulbs you are allowed to deploy on a branch circuit. 20-40 CFL bulbs will put you way over the top for a single circuit application.
Personally, I avoid CFL bulbs and deploy either T8 LFL or HID lamps in a garage space. LED might also be a good choice, but IMO CFL is not the way to go.
Part One: Lumens You Have
You have 16 feet of LFL lamps in your 8-foot/2-lamp fixture. You have 24 feet of LFL lamps in your three 4-foot/2-lamp fixtures, for a total of 40 feet of LFL lamps. Assuming that you buy premium lamps and operate them at a standard ballast factor of 1.0, a premium 4-foot F32T8 lamp will produce about 3,000 initial lumens, or 750 initial lumens/linear foot. Your 40 linear feet of lamps should put out about 40x750=30,000 initial lumens.
Part Two: Lamps You Need
Doing the second half of the math, you need enough CFL to produce the equivalent of 30,000 initial lumens. The packaging says that a typical "100W equivalent" CFL puts out 1500 initial lumens. Then you're going to need 30,000/1500 = 20 CFL bulbs to produce equivalent light output, when they are new.
Needing 20 CFL bulbs creates some logistical problems.
The first is that CFL bulbs don't retain their light output as well as linear fluroescent bulbs do. A typical CFL bulb may have it's output drop such that it's "mean lumens" rating (defined as the light output at 40% of it's rated life span) is only about 50% of the light output during it's first 100 hours of life. In other words, CFL don't preserve their light output very well, and they have a rapid fall-off in light output to about 50%.
Compare that to a standard T8 lamp which has > 80% lumen retention, or a T5 lamp that has > 95% lumen retention and you'll see that CFL bulbs are a really BAD way to light a room. They look fine when they're new, but as the bulbs age the room becomes dark and you need to deploy more bulbs to maintain the same light output. That means that if you needed 20 CFL bulbs to meet your lighting requirement according to the "initial lumens" rating, you'll probably need 40 bulbs to produce the same mean lumens over their entire rated life. 20 or 40 bulbs is an absolutely HUGE number. This is why you don't see any commercial facilities using CFL for lighting. They're always using LFL, HID or LED.
Another problem is that because CFL are not ballasted, they have a very poor power factor. They draw LOTS of current in relation to the light output they generate. This limits how many bulbs you are allowed to deploy on a branch circuit. 20-40 CFL bulbs will put you way over the top for a single circuit application.
Personally, I avoid CFL bulbs and deploy either T8 LFL or HID lamps in a garage space. LED might also be a good choice, but IMO CFL is not the way to go.
Very interesting! The problem I have is the low height of the rafters and trying to find something that doesn't hang to low. What if I used LED bulbs instead of cfl in standard sockets? How many would I need?
coralnut
Banned
I use LFL. I don't use LEDs so I can't give you advice on them. If you want to figure out the number of equivalent LED bulbs, the answer is simple: read the light specs off of the package and do the math. Follow my previous example and you can derive the answer yourself.
Platonic Solid
Well-known member
I know you won't like the price, but edge lit LED panels are your lowest profile lighting option.
23 CHIEF
Well-known member
I had height problem also I recessed drop ceiling type florescent fixtures in between the joist
I had height problem also I recessed drop ceiling type florescent fixtures in between the joist
The problem with larger lights like those are that if I want to open the hood on my truck it has to be opened between the rafters.
Edit: Just measured and the rafters are 7'3" not 8' like I thought so even worse.
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