# Square footage lighting formula



## Magnettica (Jan 23, 2007)

I was reading in the latest issue of This Old House (at the dentist office) a lighting formula using square footage of the room. It said it recommends using 3 watts per square foot (42 lumens). It did not take into effect the height of the ceiling. 

Ever hear anything like this before?


----------



## B4T (Feb 10, 2009)

I don't think you can use a "formula" for lighting a space other than one that is used as an office...

I residential.... old people want more light over the couch and less over the TV set.....

Better to have too much light than getting complaints about dark spots you have no way of fixing..

Dimmers switches are your friend.... :thumbup:


----------



## 99cents (Aug 20, 2012)

No, this is typical oversimplification by a DIY publication. An old fashioned zonal cavity calc would tell them the variables which need to be considered.


----------



## sbrn33 (Mar 15, 2007)

That is for a service calc. I think.


----------



## Celtic (Nov 19, 2007)

Magnettica said:


> I was reading in the latest issue of This Old House (at the dentist office) a lighting formula using square footage of the room. It said it recommends using 3 watts per square foot (42 lumens). It did not take into effect the height of the ceiling.
> 
> Ever hear anything like this before?




I think they simply copied *code* and interjected their own *opinion*...



> *Every room should have three kinds of lighting*: ambient, which provides overall illumination and often comes from ceiling fixtures; task, which is often found over a kitchen island or a reading nook; and accent, which is more decorative, highlighting, say, artwork. For a living room, you should have at least *3 watts *(42 lumens)* per square foot*. One visual trick Breining swears by: using uplights. "Placing a canister uplight or a torchiere in the corner will cast a glow on the ceiling, making a room seem bigger," he says.


http://www.thisoldhouse.com/toh/photos/0,,20780954_30092537,00.html


The 3W/42 lumens is a mystery to me....
http://www.rapidtables.com/calc/light/watt-to-lumen-calculator.htm


----------



## dspiffy (Nov 25, 2013)

B4T said:


> I residential.... old people want more light over the couch and less over the TV set.....


How do you account for old people like my mother, who moves the TV to a different wall in the living room every year or so?


----------



## 10492 (Jan 4, 2010)

Magnettica said:


> Ever hear anything like this before?


I think engineers use 3w sq/ft, and 5w sq/ft when doing lighting calcs as some rule of thumb.


----------



## chicken steve (Mar 22, 2011)

It comes from T220.12 ~CS~


----------



## Magnettica (Jan 23, 2007)

Ok, thought I'd ask. 

Celtic, that's the exact article too.


----------



## Javoltage (Feb 2, 2014)

*How much should i charge???*

I am installing 4 recessed lights and one single pole in a living room

and 2 lights in a bedroom with one single pole. What is a estimated price, help thanks!


----------



## FrunkSlammer (Aug 31, 2013)

Javoltage said:


> I am installing 4 recessed lights and one single pole in a living room
> 
> and 2 lights in a bedroom with one single pole. What is a estimated price, help thanks!


$150/light


----------



## Javoltage (Feb 2, 2014)

FrunkSlammer said:


> $150/light


Thank you sir


----------



## five.five-six (Apr 9, 2013)

FrunkSlammer said:


> $150/light


Is that US or Canadian? 


Sent from my iPad using Tapatalk


----------



## Rochsolid (Aug 9, 2012)

I just quoted a side job, install a recessed light in washroom, and install a new fan motor for her ceiling fan. 375$ plus materials.


----------



## FlyingSparks (Dec 10, 2012)

I have noticed stairwells are about 200lx, 450lx for an office space, etc. Though OSHA has requirements laid out 1926.56(A). Offices are 323lx minimum per osha standards. Don't do lighting calculations based on watts, that is an arbitrary way to do it in my opinion.


----------



## eTom (Feb 4, 2014)

It’s true for average premises. In fact, besides code’s recommendations, natural lighting should be taken into account. Modern buildings tend to have large windows and therefore more light.


----------



## eTom (Feb 4, 2014)

Magnettica said:


> I was reading in the latest issue of This Old House (at the dentist office) a lighting formula using square footage of the room. It said it recommends using 3 watts per square foot (42 lumens). It did not take into effect the height of the ceiling.
> 
> Ever hear anything like this before?


It’s true for average premises. In fact, besides code’s recommendations, natural lighting should be taken into account. Modern buildings tend to have large windows and therefore more light


----------



## daveEM (Nov 18, 2012)

eTom said:


> It’s true for average premises. In fact, besides code’s recommendations, natural lighting should be taken into account. Modern buildings tend to have large windows and therefore more light.


Especially at night. Right?


----------



## Mrphil (Feb 8, 2014)

We will design/build 8-10 commercial projects a year on average.
I typically use 1.25 watts per square foot on typical light commercial projects.
Standard business offices,sales areas,cafeterias,warehouses,etc.
This is standard with the engineers I use to stamp and seal if we need it.


----------

