Calculate the Light Needed for Any Space (2023)

How much light is enough to light a room? Most designers and architects use two foundational principles of lighting design when planning and specifying lighting for any space:

  • the qualitative (or aesthetic) aspect of light
  • the quantitative (or engineering) aspect of light

Calculating for total lighting required is considered quantitative.

The lumen method is the most commonly used for calculating the total light output needed for your space. With this formula, you first establish the intended use of the space, then you measure its square footage.

This guide will help you understand what the lumen method is and how to calculate it. You can also use the lumens calculator below to determine how many lumens you need based on room size and other key variables.

Table of contents:

  1. Helpful Lighting Terms
  2. The Lumen Method – How to Calculate Lumens
  3. Footcandle Requirements for Various Applications
  4. Summary: Calculating Total Lumens Needed for a Room
  5. Factoring in Lumen Lighting Variables
  6. Lumens Calculator
  7. Accounting for Personal Taste

Helpful Lighting Terms


Lumen output is a measurement of the total quantity of visible light emitted by a light source. It’s also commonly known as brightness or light output.

The reference point: A standard 100-watt incandescent light bulb produces about 1,500-1,700 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.

(Video) Lighting Calculations: Lumen Method

Each type of light source — LED, fluorescent, halogen or incandescent bulbs — has a different lumen-to-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 bulb may claim 100-watt equivalency and energy efficiency.

Here’s a lumen-to-watt chart. Please note that these ratios may vary slightly, even between different LED products.


Foot-candle is the original measurement system for light intensity on a one square-foot surface from a uniform source of light. In other words, a foot-candle 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 a footcandle chart on how many foot-candles of light humans need to perform tasks comfortably in different spaces.

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

The Lumen Method – How to Calculate Total Lumens Needed

  1. Determine room size by 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 requirement for your application. Lighting requirements vary depending on the type of room being lit, also known as the application. For example, a bathroom or kitchen will require more foot candles than a living room or bedroom. Once you establish the intended use of your space, browse this footcandle chart for the IES-recommended footcandle requirement for your application.
  3. Multiply the room square footage by the footcandle requirement. For example, a 100 square-foot living room, which needs 20 foot-candles, will need 2,000 lumens. A 100 square-foot dining room, which needs 40 foot-candles, will require 4,000 lumens.
Calculate the Light Needed for Any Space (3)
Calculate the Light Needed for Any Space (4)

We’ve created a helpful guide to How Many Lumens You Need that walks you through this calculation in more detail.

Commercial Lighting Footcandle Requirements

RoomFoot-candles Needed
Offices: Average Reading and Writing50-75
Offices: Hallways10-20
Offices: Rooms with Computers20-50
Auditoriums / Assembly15-30
Hospitals: General Areas10-15
Hospitals: Labs / Treatment Rooms75-100

Residential Lighting Footcandle Requirements

RoomFoot-candles Needed
Living Room10-20
Kitchen: General30-40
Kitchen: Stove70-80
Kitchen: Sink70-80
Dining Room30-40

Summary: Calculating Total Lumens Needed for a Room

Let’s recap how to gauge how much light you need for a space. Multiply your room square footage by the footcandle requirement. For example, a 100-square foot living room, which needs 20 foot candles, will need 2,000 lumens. A 100-square foot dining room, which needs 40 foot-candles, will need 4,000 lumens.

(Video) How Much Light Does My Room Need? Lighting Design | Lighting Calculation Formula

Download a Free Footcandle Chart »

Factoring in Lumen Lighting Variables

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 lumens calculator below will be sufficient for determining the required light output for your application.

If you have high ceilings in a space, then you must account for that in your lumens calculation. You do that with a footcandle multiplier.

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

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’s square footage.

Wall Color Variable

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

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Lumens to Candlepower Conversion

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

Lumens Calculator

Use this calculator to calculatethe lumens needed to light a room.


Please note that these are estimations. For exact analysis, please consult a lighting design professional.

Accounting for Personal Taste

Personal preference will play a large rolein determining how much light you need in a space. If you like the room to be especially bright, you may want to add an additional 10-20% to our numbers and then install dimmers to adjust the light to desired levels.

When lighting is properly designed in a space, you notice the room and the objects in it. In other words, you notice what the lighting illuminates, not the lighting products themselves. Bad or deficient lighting design shows up as hot spots, dark spots and unintentional shadows.

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Good or efficient lighting design accounts for total general and task lighting required for a space. Dynamic or superior lighting design factors the qualitative, human experience. It lights for vertical (not merely horizontal) visual impressions, such as walls — as well as ceilings with uplighting to minimize shadows and dark spots for smooth, streamlined and evenly distributed light.


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Calculate the Light Needed for Any Space (5)

David Hakimi

Alcon Lighting creative director and co-founder David Hakimi works to improve lighting through research, development and education. David strives for efficiency in lighting, affording architects, lighting designers and engineers the ability to maximize LED lighting design and application.David is a graduate of the University of California, Los Angeles, where he received a Bachelors in history. David also studied lighting design at IES in Los Angeles. He traces his and Alcon Lighting’s commitment to innovation, accountability, quality and value to lessons learned from his father, Mike Hakimi, a lighting craftsman, salesman and consultant in Southern California for more than four decades.Today’s lighting for commercial use requires a deep, complete understanding of smart lighting systems and controls. David takes pride in his lighting, energy controls and design knowledge. He is driven by the desire to share his insights into lighting specification and application. This quest to share his knowledge was the impetus for David to create Insights, Alcon Lighting’s blog and resource center for helping the reader understand lighting and its application to space.

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How do you calculate lighting needed? ›

To determine the needed lumens, you will need to multiply your room square footage by your room foot-candle 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.

How much light do I need for a 12x12 room? ›

As a handy rule of thumb, a sitting room or bedroom will generally require around 10-20 lumens per square foot, while a bathroom or kitchen will need a stronger level of lighting, at around 70-80 lumens per square foot. To work out the lumens you need, simply multiply the square footage of the room by this figure.

How do you calculate the number of lighting fixtures in a certain area? ›

Multiply width of room x length of room x 1.5 = amount of total minimum wattage needed (assuming an eight foot ceiling). Divide by 60 to get the number of 60-watt equivalent bulbs required. Then, add up the wattage in each bulb in each fixture to figure out how many light fixtures are needed.

How many lights are needed for a 10x10 room? ›

How many plants per LED grow light?
Grow Room SizeSquare FeetRecommended # of Plants in Veg
6' x 6'36Up to 36
4' x 8'32Up to 32
8' x 8'64Up to 64
10' x 10'100Up to 100
6 more rows
5 Mar 2021

What is the formula for lighting ratio? ›

Since the lighting ratio is the ratio of the light levels on the brightest lit to the least lit parts of the subject, and the brightest lit are lit by both key (K) and fill (F), therefore the lighting ratio is properly (K+F):F although for contrast ratios of 4:1 or more, then K:F is sufficiently accurate.

How do you calculate lighting load per square foot? ›

Table 220.12 in the National Electrical Code considers a residence a listed occupancy at 3 VA per square foot; therefore, the general lighting load is determined by multiplying the square footage. For example, 2,800 square feet times 3 VA is 8,400 VA.

How do you calculate the daylight factor of a room? ›

Daylight Factor = \frac{(45 \times Window Area\times Light Transmittance)}{(Total Room Surface Area \times 0.76)}

How many lights do you need per foot? ›

“A good rule of thumb is 100 lights for every foot-and-a-half of tree,” according to Lowe's. But Better Homes & Gardens recommends using three 100-light sets for every foot of a tree's height. And Real Simple suggests 100 lights for every foot.

How many can lights per area? ›

A common rule of thumb is that you use one recessed light for every 4 to 6 square feet of ceiling space. Doing so provides even, overall illumination.

How many watts do I need to light a room? ›

The Formula for Lighting a Room

So if you have an 18' long room x 12' wide room multiply times 1.5 = 324 watts, that's how much wattage is needed to adequately light the room. You can divide that lighting into more than one source.

How do you calculate lighting layout? ›

Determine the number of lights that will be in each row and column. Divide the total length of the row by the total number of lights in the row to determine the spacing between lights. Divide the spacing between the lights by 2 to determine the distance between the wall and the first light.

How many lumens is a 10x10 room? ›

For every 100 square feet, 1000 lumens is sufficient for low-light level areas such as living rooms and lounge areas, while task-oriented spaces may require up to 3000 lumens or more.

What is lux of normal room? ›

In homes- The recommended illumination levels for homes is often 150 lux. The living and dining rooms may work pretty well with about 25 to 50 lux. Supermarkets- Working spaces like supermarkets and mechanical rooms require light levels of about 750 lux.

What is the lux formula? ›

The LUX level in a room is calculated from the following formula. E(LUX) = F(lm) x UF x MF / A.

How many can lights per room calculator? ›

Formula: total sq. footage x 1.5 = total wattage needed. Total wattage divided by 60 watts (or whichever wattage you select) = total amount of recessed can lights. Example: 240 square foot room x 1.5 = 360 divided by 60 (the bulb wattage I'd like to use) = 6 recessed lights needed.

How much light do I need for a 8x8 grow room? ›

These monstrous grow tents will require a spare room or garage to be set-up in due to their large size. The 8x8 footprint of this these tents will need about four or so 600 watt or equivalent grow lights to fully cover the space.

What size can light for 10 foot ceiling? ›

Designers typically recommend allowing 2 ½ inches to 3 inches of chandelier for each foot of ceiling height. For 10 foot ceilings, choose a chandelier that is between 25 inches and 30 inches tall, including the canopy, light and chain.

What is the 80% rule in lighting? ›

This rule states that an OCPD can be loaded to only 80% of its rating for continuous loads. Remember that 80% is the inverse of 125% (0.80 = 1 ÷ 1.25) and, as such, the rules are indeed identical in their end requirement.

How do you calculate the load of a room? ›

For a room, multiply its length by its width to get the square footage. Multiply the square footage by 20. This is the measure of the BTU cooling load of the space.

How do you calculate watts in a room? ›

Wattage: Multiply the area in feet by 10. For a room 20 feet by 20 feet, we obtain 400 sq. ft., multiplied by 10 to give 4000 watts. The number of watts = area x 10.

How many watts of light do I need per square foot? ›

The general rule of thumb for providing light for an area is a minimum of 30 watts per square foot. 50 watts per square foot is optimal.

What does 2% daylight factor mean? ›

Rooms with an average DF of 2% are considered daylit. However, a room is only perceived as well daylit when the DF is above 5%. Daylight factors are always measured under an overcast sky or in an artificial sky which simulates a standard CIE overcast sky.

How do you calculate daylight factor manually? ›

Daylight Factor is typically calculated by dividing the horizontal work plane illumination indoors by the horizontal illumination on the roof of the building being tested and then multiplying by 100.

How do interior designers calculate light? ›

So to know how many lumens you need, you just multiply the Lux by the area. So in this example 120 Lux x 12 square metres = 1440 Lumens. So to light the room you need either one bulb of 1440 Lumens or several bulbs which add up to 1440 Lumens.

What is the 50/50 rule right to light? ›

A right to light is a legal right to a particular amount of light in a room or space. Using the 50:50 rule, a right to light injury is defined as loss of light when the light within a room is reduced to less than 50% of the original amount. Not everyone has a legal right to light, so it's best to check.

How many lumens do I need per square foot in an office? ›

A lumen is simply a measurement that describes the amount of light produced by a bulb or fixture. Using the list, you'll see that an office would need an average of 40 foot-candles or 40 lumens per square foot.

How many feet of lights do I need for a 7ft tree? ›

Basic Rule of Thumb

"So an easy, general rule to remember is that for each foot of your tree, you'd want to use one strand of lights.

How far to space 6 can lights? ›

If a 6-inch light has a spacing criteria of 1.5 and the ceiling height is 8 feet, the maximum space between each light should be 12 feet. This formula is critical for lighting a space because if the lights are too far apart, they will look like spotlights with big shadows between each other.

How many can lights for a 12x12 kitchen? ›

How Many Recessed Lights? In general, a 12x12 kitchen will use a minimum of three to a maximum of nine recessed lights to illuminate the needed area. Exact lighting needs will vary, so keep your kitchen's layout in mind when deciding the number of lights you need for your unique space.

How many can lights for 18x18 room? ›

Divide the distance of the room (width or length) by the number of bulbs in a row. So for the length of the room, say it was 18 feet. You will use six bulbs in total, in two rows of three.

How many rooms are there in 1 watt hour? ›

Thus, there are 3600 Joules in one watt-hour. Q.

Can a 60-watt bulb light a room? ›

Example: If your light fixture uses 60-watt lightbulbs: 288/60 = 4.8. Therefore, your room needs a light fixture with a minimum of five lightbulbs or a total of roughly 288 watts (including other lighting sources in the room).

How many 1000 watt lights can I run? ›

A 1000w HPS or Metal Halide light takes 9 amps at 120 volts so you can only run one on a wall outlet circuit. A standard dryer outlet is 220 volts and 30 amps so you can power up to six 1000 watt lights on that circuit.

How many lumens do I need for a 20x20 room? ›

So, let's say it is a 20 x 20 ft room, giving us 400 sq ft. And let's say you have a six-light pendant using 9W LED bulbs that put out 840 lumens each. 840 x 6 = 5,040 lumens. Dividing the lumens by the square footage, you find you're getting about 13 lumens-per-square-foot (5,040 ÷ 400 = 12.6).

HOW FAR CAN 1000 lumens go? ›

A 1000 lumen flashlight is quite bright and, depending on the lens or reflector design, powerful enough to reach a distance of 200 meters or more. This type of flashlight allows you to see objects from a far distance.

Can 800 lumens light up a room? ›

A couple of 400 lumen spotlights would work well, but if you've just got the one light source, an 800-1000 lumen bulb will work, too. And like the kitchen, you want a cool temperature to keep you motivated. A bathroom is probably the trickiest room in the house.

How many lux is a TV? ›

TV and film sets are lit at about 600 lux. a bright office has about 400 lux.

How many lux is a 100 watt light bulb? ›

To replace a 100 watt (W) incandescent bulb, look for a bulb that gives you about 1600 lumens.

How many lux is a dark room? ›

Some might classify 32 lux as working in darkness. Even a 100-watt, soft white, incandescent reading lamp in a room with no other illumination, off-white walls, and low ceilings measures about 350 lux at about two feet from a shaded source.

How much lux do I need? ›

In areas where we do tasks like reading, it is recommended to increase the LUX to 200. environment, around 500 LUX is needed. In the workshop area where detailed work is done the recommended level is 500-700LUX. For spaces like the operation theatre of the hospital, the LUX level should be around 1000.

How do you measure lux of light? ›

Lighting professionals use a light meter (also called an illuminance meter or lux meter) to measure the amount of light in a space/on a particular work surface. The light meter has a sensor that measures the light falling on it and provides the user with a measurable illuminance reading.

How many lux is a watt? ›

Thus, your 1 W LED lamp gives us 0.9 lux for 1 watt. Now, you can compare the result with another light source using our watts to lux calculator.

How do you calculate kW for lighting? ›

Going from watts (W) to kilowatts (kW) is a pretty straightforward calculation: 1kW is equal to 1,000W. To convert W to kW, divide the total wattage by 1,000. Here's an example: if you turned on ten 100W light bulbs, that would equal 1kW of energy usage.

What does 400k mean in lighting? ›

It is the scientific measurement for the color of the light itself. Higher numbers are nor brighter, just whiter such as 5000K and eventually more blue like 5700K. Lower numbes such as 4000K appear off white or a tinge of yellow and 3000K is warm in color meaning that the are brown or yellow in tint.

How do you calculate light wattage for a room? ›

Wattage: Multiply the area in feet by 10. For a room 20 feet by 20 feet, we obtain 400 sq. ft., multiplied by 10 to give 4000 watts. The number of watts = area x 10.

How is power of light calculated? ›

Incandescent Lighting: Watts* X hours per day = watt-hours per day; X days per year = watt-hours per year; ÷ 1,000 = kWh per year; X energy cost per kWh = total annual energy cost. Fluorescent and HID Lighting: Watts* X hours per day = watt-hours per day; X days per year = watt-hours per year; ÷ 1,000 = kWh per year.

How many kW is a light? ›

On average, incandescent light bulbs use about 60 watts of electricity, and LED light bulbs use about 10 watts. Using an incandescent light bulb for 2 hours per day will use about 12.2 kilowatt-hours of electricity per month and 43.8 kilowatt-hours of electricity per year.

What is brighter 3000K or 6000K? ›

The lower the Kelvin numbers the yellow the color of the lights gets whereas, with higher Kelvin number, the light gets whiter and brighter.

Which is brighter 3000K or 5000K? ›

5000K is surely brighter than the 3000K warm white light.

It's closer to broad daylight and that's why it's suitable for parking lots, large outdoor venues, and industrial lighting installations. In fact, the blue light emitted by a 5000K LED can appear to be colder than the room itself.

Is 6000K too bright? ›

6000K is a cool color temperature and defined as “Day White” color. Usually, cooler light be perceived as” bright enough” and look awesome if when they come to automotive lighting. The color temperature 6000K has the satisfied conditions as above mentioned.

What are the 3 rules of lighting? ›

Three-point lighting is a traditional method for illuminating a subject in a scene with light sources from three distinct positions. The three types of lights are key light, fill light, and backlight. Key light. This is the primary and brightest light source in the three-point lighting setup.

What do you mean by 80/20 rule? ›

The 80-20 rule, also known as the Pareto Principle, is a familiar saying that asserts that 80% of outcomes (or outputs) result from 20% of all causes (or inputs) for any given event. In business, a goal of the 80-20 rule is to identify inputs that are potentially the most productive and make them the priority.

Which technique is 80/20 rule? ›

The Pareto principle (also known as the 80/20 rule) is a phenomenon that states that roughly 80% of outcomes come from 20% of causes. In this article, we break down how you can use this principle to help prioritize tasks and business efforts.


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