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.
Table of Contents
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.
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
- 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.
- 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.
- 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
|Offices: Average Reading and Writing||50-75|
|Offices: Rooms with Computers||20-50|
|Auditorium / Assembly||15-30|
|Hospitals: General Areas||10-15|
|Labs / Treatments Rooms||75-100|
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.
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
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.
Alcon Lighting creative director and co-founder David Hakimi works to achieve efficiency in lighting, affording architects and lighting designers and engineers the ability to maximize ideal lighting. David takes pride in the company’s design, energy and building knowledge, tracing the commitment to add value to lessons learned from his Southern California lighting trade and craftsman father. David aims to assure that each customer complies with codes and achieves project goals with artistry, economy and excellence.
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?
Hi Sue, without knowing the square footage of your space, including your ceiling height and the color of the walls, it’s hard to say. Alcon Lighting generally recommends going with odd numbers for design aesthetics, however, in this case, I suggest you consider going with four fixtures and use a… Read more »
It is basically 9×15 with a jut out on one end of the room. It is an interior room with NO windows. The ceiling is 9 ft high and no paint color has been decided on yet.
Do you know the lumen output of the fixtures you’d like to install?
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!
Hi Edward, thanks for reading the lumen output post. Please clarify and describe what you’ve identified as the discrepancy and I can look into it.. What are the numbers you’re plugging in?
I have looked at my figures again and I realise where I was going wrong; I was converting from m sq to ft sq using an incorrect calculation.
Now that I’ve corrected, there’s not so much of a difference between the calculator and my workings out!
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?
(1) What’s the ceiling height?
(2) Does the office have windows?
(3) Are the lights dimmable?
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 »
It sounds like you may be overwhelmed by the project. I’ll try to help, if only by referring you to resources. Do you have a specific question?
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?
Doug, good luck with your project. Yours is a project-specific information request. We certainly welcome general requests and would love to help. However, it’s easier for Alcon Lighting to help when you send a message. Please feel free to send a detailed message so we can try to help. Thanks… Read more »
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 »
James, good luck with your project. Yours is a project-specific information request. We certainly welcome general requests and would love to help. However, it’s easier for Alcon Lighting to help when you send a message. Please feel free to send a detailed message so we can try to help. https://www.alconlighting.com/support/
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?
Based on the details you provided, I recommend around 3000 lumens but 2300 lumens should be sufficient light for your foyer as well. Good luck!
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.
You divide 4000 by 6 fixtures to get the needed lumen level per fixture.
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?
The suggestion is for recessed downlight layout designs.
Wow. Consise factual and easy to understand. Plus imbedded calculator.
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 »
Hi Kathy! Multiply the 3,200 by the recommended foot candles for a party room to get the total number of lumens you’ll need for the space. I recommend 15-30 but that’s ultimately up to you and your designer. Reference the chart in the post. Aim for 30 foot candles with… Read more »
thanks- that helps 🙂
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 »
You could also add an adjustable ceiling mount spot light or a directional floor lamp. Good luck!
Thanks again. I really appreciate it.
What kind of lighting is best for overhead tube light in kitchen….Cool, Warm, Bright? is 4000K too bright?
A cooler, 4000K light color temperature serves as a better work light. In this case, cooking or baking.
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?
Please refer to this post:
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?
Yes, Richard. You’re exactly right.
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.
So enjoyed your article on ‘How to Determine how many Lumens you’ll need to properly light your space’. So clear, so brilliantly explained…..at 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 »
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 »
If you would like to use the lamp with all other lights off in the room, and still be able to read, I’d double that lumen count to 400 at least. 400-500 lumens to be safe.
Glad you found the post useful. Good Luck.
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.
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 »
Hi John, Great questions. Here’re the answers. 1. You wrote that “one could see with better clarity in a room lit with LED lumens compared to one lit with the equivalent number of fluorescent, incandescent or halogen lumens.“. Is there a conversion factor to be used when making LED bulb… Read more »
David Thank you for the prompt replies as I expect you are a rather busy person ! I think I understand what you are saying about beam spread….. if a 600 lumen down facing ceiling led light fixture has a 45 degree beam spread then the light circle diameter would… Read more »