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Lighting the Interior: How to Calculate Total Light Output for Your Space

Lighting the Interior: How to Calculate Total Light Output for Your Space

How much light is enough? Most designers and architects use two foundational principles of lighting design when planning and specifying lighting for any space —the qualitative (or aesthetic) aspect and the quantitative (or engineering) aspect of light. Calculating for total lighting required is considered quantitive.

Use the lumen method, the most commonly used light output formula, to calculate the total light output needs for your space. First, establish the intended use of the space, then, measure its square footage. 

Here are a few key terms. 

Lumen output, also known as brightness or light output, is a measure of the total quantity of visible light emitted by a light source. The reference point: a standard 100-watt incandescent light bulb produces about 1,500 to 1,700 lumens. Strictly speaking, 600 LED lumens provides the same amount of light as 600 incandescent lumens. LED lights provide higher Color Rendering Index (CRI), so, while they more accurately reveal the colors of the subject being lighted, they don’t provide more light.

Wattage is a measure of how much electricity (or energy) a light bulb consumes to achieve its lumen output. Each type of light source—LED, fluorescent, halogen or incandescent—has a different lumen-per-watt ratio. If a 100-watt incandescent light produces 1,500 lumens, and a 10-watt LED light does the same, the 10-watt LED light may claim 100-watt equivalency and energy efficiency. 

Here’s a lumen-to-wattage ratio chart. Please note that lumen-per-watt ratios may slightly vary, even from LED to LED products.
In this image we see a chart showing the wattages used by LED, fluorescent, halogen and incandescent light bulbs to achieve the same average lumen output.
Footcandle is the original measurement system for light intensity on a one square foot surface from a uniform source of light. In other words, a footcandle is the light measured one foot away from a candle. Considering the human-centric principles of lighting design, the IES, the largest society of professional lighting designers, provides recommendations of how many footcandles of light humans need to perform varying tasks and comfortably occupy various spaces. 

For example, for washing dishes, they recommend that your lighting provides 20 footcandles of light at two feet, six inches off the floor. This is also referred to as the horizontal target.

The Lumen Method
Calculating total lumen output required for your application

  1. Determine room square footage. Multiply the length times the width of the room to get the room square footage. For example, if the room is 10 feet wide and 10 feet long, the room square footage will be 100 square feet.
  2. Establish the footcandle requirements for your application. Lighting requirements vary depending on the type of room being lit. For example, a bathroom or kitchen will require more footcandles than a living room or bedroom. Once you establish the intended use of your space, browse this light level chart for the IES recommended footcandle requirement for your application.
  3. Multiply room square footage by the footcandle requirement. For example, a 100 square-foot living room, which needs 20 footcandles, will need 2,000 lumens. A 100 square-foot dining room, which needs 40 footcandles, will require 4,000 lumens.11 See PDF and complete foot candle index.

Here are some suggested footcandle recommendations
By use, space and application

Commercial Requirements
Room Footcandles Needed
Offices: Average Reading and Writing 50-75
Offices: Hallways 10-20
Offices: Rooms with Computers 20-50
Auditorium / Assembly 15-30
Hospitals: General Areas 10-15
Labs / Treatments Rooms 75-100
Libraries 50-100
Schools 30-100
Residential Requirements
Room Footcandles Needed
Living Room 10-20
Kitchen General 30-40
Kitchen Stove 70-80
Kitchen Sink 70-80
Dining Room 30-40
Bedroom 10-20
Hallway 5-10
Bathroom 70-80


Lumens calculation 
Determining how much light you need for any room is simpler than you probably imagined. Multiply your room square footage by the footcandle requirement. For example, a 100 square foot living room, which needs 10-20 foot-candles, will need 1,000-2,000 lumens. A 100 square foot dining room, which needs 30-40 foot-candles, will need 3,000-4,000 lumens.21 See PDF and complete foot candle index

Ceiling Height Variable

Note: Only read this section if your ceiling height is taller than 10ft. If your ceiling height is below 10ft, the Lumen Method above and the calculator below are sufficient tools for determining the required light output for your application.

To calculate for your recommended footcandle multiplier, use the following formulas:

recommended footcandles (fc) = cd ÷ h

cd = candlepower

h = distance between the lamp and the horizontal target

See Also

Once you determine your desired footcandle level, you multiply that by your room square footage.

Our calculator assumes a standard 8-foot ceiling. It then uses averages and recommended light levels to calculate for different ceiling heights. Please note, these are estimations.  For exact analysis, please consult a lighting design professional.

If you have especially dark colored walls and furniture or if you’re using fixtures with shades, you’ll need roughly an additional 10 lumens per square foot.

Candlepower is a unit of measurement for luminous intensity. It expresses levels of light intensity relative to the light emitted by a candle of specific size and constituents. The historical candlepower is equal to 1.02 candelas. In modern usage, candlepower is sometimes used as a synonym for candela.

Lumen output = C/0.07958

For example, 200 candlepower would equal: L = 200 candlepower / 0.07958. Do the division using a calculator: 200 candlepower / 0.07958 = 2 513 lumens.

Lumens Calculator  


Measurement Unit

Illumination Intensity
Wall Color
Light Placement

Finally, personal preference will play the largest part in your decision. If you like the room to be especially bright, you may want to add an additional 10 to 20% to our numbers. In fact, the best approach for most spaces is to aim high and install dimmers to bring the light level down to desired levels.


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I saw some lights with 60 watt bulb capacity and want a well lit dining room. Would three pendant lights work or would 4 be better for a space with no outside light coming in?'

I’m not sure if the manual calculation or the calculator is incorrect, but when I compare results, they differ. I checked and recheck so I don’t know which result to believe!'

In a roughly 20×20 office space we have 6 2×2 flush led ceiling lights. They are 4,000 lumens. Is this too much?'

I am finding your answers to others thoughtful and beneficial so I decided to throw my questions out there. We were at a store today looking at lighting and I found myself getting quickly overwhelmed. We are building our house and are just beginning the wiring phase and no light… Read more »'

Hi there,I have a 13 x18 kitchen with 1 window,light colored walls and 8′ ceilings
Want to use led lighting,os 5200 lumens good?'

I have a shop that is 16 x 32 x 14 high I bought 8 2×2 4 tube led lights which are 5000 lumens each I believe 4000k. I plan on hanging them in 2 straight lines, in each line they will be @ 4 foot apart and @ 8… Read more »'
How much LED lights would I need for a 25 foot fla

How much LED light would I need for a 25 foot flagpole'

Is 2300 lumens enough light to properly illuminate a 12 x 15 foyer with 16 foot ceiling?'

Wow! Thank you so so much I really needed to read this and know more. Also I have a question if you can help, so you know the deference between the led light and the grow light for plants? Can I use the normal led let ( with high Lumen)… Read more »'


Perhaps I missed it, but if a measured kitchen space needs 4000 lumens and has 6 recessed ceiling lights, do you divide 4000 by 6 to get a per-fixture lumen level ? Or buy 6, 4000 lumen recessed (retrofit) fixtures (with dimmer?)? Thank you in advance.'

Thank you for this helpful article. There is a diagram at the end entitled “Preferred LED Lighting Layout” that suggests LED lights should not be placed in corners. Does this apply to any type of LED lights or only to downlights?'

Wow. Consise factual and easy to understand. Plus imbedded calculator.
Good job'
Timothy Brady

This is great information. My wife and I are struggling right now trying to get the right lighting in a home we bought. We just recently had installed 4x LED can lights but we are unsure of the Lumens but are pretty certain it is not enough. Our estimation is… Read more »'

I have a 3200 sq ft large party room (an almost square space) with 10-12 ft ceilings (slight vault). I’d like to do recessed downlights as the main source of light. The walls are a light color. If my fixtures each provide 1200 lumens, how many fixtures will I need?… Read more »'

Thanks very much for this resource! I am trying to light a basement art studio that has no natural light. It’s about 14′ x 20′; the ceiling is between 6′ and 7′, depending whether one measures from the top or bottom of the beams across it. Your calculator says I… Read more »'

What kind of lighting is best for overhead tube light in kitchen….Cool, Warm, Bright? is 4000K too bright?'
Duane Kerr

If I want to install in-ground well lights (2) to shine up at a 5′ x 8′ flag on a 35 foot pole, how many lumens should each light fixture be?'


I understand this is rough estimate as there are other factors. My question is, if I determined my needed lumens on the entire room, should I divide it to number of fixtures/downlights?'
J. Guckert

What a wonderfully well-written, informative piece. I’m a picky, writer-type, from the technical and non-fiction arenas, and I love finding such good writing scattered around the web, in non-obvious places.'
Shiva Shrestha

Nice explanation'

So enjoyed your article on ‘How to Determine how many Lumens you’ll need to properly light your space’. So clear, so brilliantly explained… least 100,000 lumens worth!'

Thank you for such crystal clear text and the usefull tool available that allow us to do quick calculations.'

I found this article while researching about IES profiles for a game developer. We have the ability to use IES profiles for each light source in our development tools, but I needed to find a good source on how much lighting to use in each “room” to help narrow down… Read more »'
Terry B

Hi David, This is such a helpful and well-written blog entry. Perhaps you can offer me a suggestion. I am looking for a lamp for a bedside table, specifically to have enough light to be able to do light reading or paperwork (eg, paying bills) before going to sleep. I… Read more »'

I just wanted to say what an absolute gem of a website you have here. I live abroad and am not able to purchase from yourselves, but just wanted to say thank you for such as awesome blog and help.'

Hi, you should check the calculator on this page – the output for meters compared to feet is way off.'
John McHardy

First let me say how grateful I a that I found this blog – your explanation of how to determine the total amount of light required for a rec room I am building was easy to understand and has moved me significantly closer to understanding how many led pot light… Read more »