# 2x4 florescent calculation



## zen

is this the right formula to find out how many 2x4 lay in lights i need for a room?
room is 12 x 12 =144 sq. ft. divide by 32 watts per bulb =4.5 divide by 3 lamps per fixture = 1.5 which rounds up to 2 fixtures per room.

next we have 80 2x4 s to change out...no problem except once we got started we found in many rooms they piped straight from one fixture to the next,,setting a 4 sq. box on top of the fixture to feed the light piping out of the side of the 4 sq. to the next light,,,,no ceiling wires to the fixture and they straped the emt to each fixture...to change these out it looks like we will need to bring all this up to code....in this case would it have been better to retrofit these light so they would be considered existing...im sure my boss told the customer although this was bid the price has to change for the labor and material...any suggestions would be helpfull


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## erics37

If the fixtures have an information tag or label, use the rated power on that. If not, use the info on the fixture ballast(s). Don't just add up all the light bulbs.

How many lights you install per room depends on how bright you want it.

And on your fire system in your other thread, you were supposed to make the exhaust fan come on even if it was off, in the event that the system was actuated.

Do you have much commercial experience?


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## BBQ

zen said:


> is this the right formula to find out how many 2x4 lay in lights i need for a room?
> room is 12 x 12 =144 sq. ft. divide by 32 watts per bulb =4.5 divide by 3 lamps per fixture = 1.5 which rounds up to 2 fixtures per room.


:blink::blink:

The watts have nothing to do with how many fixtures are needed. 

When you do circuit calculations the code requires you use the rating on the ballasts not the lamps.


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## chicken steve

take a look @ 220.12

~CS~


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## BBQ

zen said:


> is this the right formula to find out how many 2x4 lay in lights i need for a room?





chicken steve said:


> take a look @ 220.12



:blink::blink::blink::blink:

There is nothing in the NEC that tells us how many lights a room needs.


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## chicken steve

BBQ said:


> :blink::blink::blink::blink:
> 
> There is nothing in the NEC that tells us how many lights a room needs.


 
i made no claim there was BBQ ~CS~


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## zen

i was trying to find lumens per sq. ft.......but as ive searched older post i have nt seen any calculations,,,,the formula i use is based on 8 ft. ceiling in office spaces..not sure how it was created ,,im guessing watts represents/converts to lumens once divided into sq.ftage,,,,


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## chicken steve

i suppose you can solicit the photometrics from any given lighting manufacturer Zen

~CS~


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## BBQ

chicken steve said:


> i made no claim there was BBQ ~CS~


Silly me, I assumed you were trying to answer the OP. I did not know it was 'post a random code section for fun day'. :thumbsup:


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## chicken steve

BBQ said:


> Silly me, I assumed you were trying to answer the OP. I did not know it was 'post a random code section for fun day'. :thumbsup:


and just how many lighting formula sources exist to make the nec random ?

~CS~


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## McClary’s Electrical

zen said:


> i was trying to find lumens per sq. ft.......but as ive searched older post i have nt seen any calculations,,,,the formula i use is based on 8 ft. ceiling in office spaces..not sure how it was created ,,im guessing watts represents/converts to lumens once divided into sq.ftage,,,,


 I have no idea how it works on paper but there are plenty of online calculators that will figure this for you


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## chicken steve

from MD's thread>

http://www.relux.biz/

~CS~


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## noarcflash

Just change them out, 1 for 1. and they'll still be saving electric, and have more light.

at 1st, they will think it's too much light, but the tubes dim out some in time.


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