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:
Helpful Lighting Terms
The Lumen Method – How to Calculate Lumens
Footcandle Requirements for Various Applications
Summary: Calculating Total Lumens Needed for a Room
Factoring in Lumen Lighting Variables
Lumens Calculator
Accounting for Personal Taste
Helpful Lighting Terms
Lumen
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
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 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
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
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.
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.
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.
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
Room
Foot-candles Needed
Offices: Average Reading and Writing
50-75
Offices: Hallways
10-20
Offices: Rooms with Computers
20-50
Auditoriums / Assembly
15-30
Hospitals: General Areas
10-15
Hospitals: Labs / Treatment Rooms
75-100
Libraries
50-100
Schools
30-100
Residential Lighting Footcandle Requirements
Room
Foot-candles 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
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.
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.
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.
LUMEN/WATT CALCULATOR
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.
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.
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.
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.
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.
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.
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.
Multiply the length by the width and you'll have the square feet. Here's a basic formula you can follow: Length (in feet) x width (in feet) = area in sq. ft.
A light-year is a measurement of distance and not time (as the name might imply). A light-year is the distance a beam of light travels in a single Earth year, which equates to approximately 6 trillion miles (9.7 trillion kilometers).
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.
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.
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.
How much area does the 6-inch recessed light cover? The general rule is to space the recessed lights according to their diameter. So, a 6-inch recessed light should be placed at a distance of 6 feet. In other words, a 6-inch light would cover 6 feet of ceiling space.
How to determine how much light you need in watts: 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.
For a room with decent natural light, that should be around 60 watts. For a room with few/no windows, balance the 60 watt desk light with ambient overhead lights or bump that number up to 75 watts.
A space consists of selected mathematical objects that are treated as points, and selected relationships between these points. The nature of the points can vary widely: for example, the points can be elements of a set, functions on another space, or subspaces of another space.
It is based upon carefully maintained atomic clocks and is highly stable. The addition or subtraction of leap seconds, as necessary, at two opportunities every year adjusts UTC for irregularities in Earth's rotation.
The area is the amount of space within the perimeter of a 2D shape. It is measured in square units, such as cm², m², etc. You can think of area as the area inside a given shape or space. It refers to how much space is taken up.
Lux (lx) Lux is basically the unit of illumination and is equal to one lumen per square metre. One lux equals 0.0929 footcandles and this is the metric equivalent of foot-candles. It is also known as a metre-candle.
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.
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.
According to our current data, the average wattage required per square foot is 32 watts (although this also depends on the plant, so we are taking averages here), so a 4×4 tent theoretically requires 512 watts for complete coverage. This number can float between 500 watts and 600 watts.
The 3VA per sq ft rule includes general lighting and all 15A and 20A, 125V general-use receptacles, but doesn't include small-appliance or laundry circuit receptacles. Therefore, you must calculate those at 1,500VA per circuit. See 220.14(J) for details. Number of branch circuits.
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).
If you'd like to watch movies using a projector on a 100”~120” screen without ambient lighting, around 1500~2000 lumens of projection brightness is ideal. If you need to turn on ambient lighting or if there are bright light sources in the room, a projector with 3,000 lumens or more will display clear images.
If you plan to illuminate an entire wall or accent particular architectural features or pieces of art, the rule of thumb is to place your recessed light fixtures between 1.5 feet and 3 feet from the wall. If your fixtures are fixed, they should be placed a bit closer to the wall.
How many Christmas lights per foot of tree? For every foot of your Christmas tree, you'll need 100 to 200 lights, depending on how bright you'd like your tree.
To determine how many lightbulbs your light fixture needs for a given room, calculate as follows: Take the number of watts you got when you calculated the required wattage and divide it by the lightbulb's wattage number. Example: If your light fixture uses 60-watt lightbulbs: 288/60 =4.8.
You should check the label on the lamp to find out what lightbulb wattage to use. Most lamps can accommodate a maximum of 60 watts, and you shouldn't exceed the maximum wattage. However, you can use a lower wattage lightbulb than the stated maximum, even if it's brighter than average.
Minimum of 3 foot-candles: Concrete placement, evacuation and waste areas, loading platforms, active storage areas, refuelling, and field maintenance areas. Minimum of 5 foot-candles: The standard lighting for general construction areas, warehouses, corridors, hallways, and exit ways.
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.
All assigned work areas on any vessel or vessel section—5 lumens. Landside tunnels, shafts, vaults, pumping stations, and underground work areas—10 lumens. Landside work areas, such as machine shops, electrical equipment rooms, carpenter shops, lofts, tool rooms, warehouses, and outdoor work areas—10 lumens.
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.
In general, the more detailed the task, the greater the light requirement. A process control room should be lit at an illuminance of 300 lux, a corridor or walkway may only require 50 lux, whilst studying an engineering drawing may require 750 lux (see HSG38 Lighting at Work).
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.
80% of crimes are committed by 20% of criminals.80% of sales are from 20% of clients.80% of project value is achieved with the first 20% of effort.80% of your knowledge is used 20% of the time.
The Pareto principle states that for many outcomes, roughly 80% of consequences come from 20% of causes. In other words, a small percentage of causes have an outsized effect. This concept is important to understand because it can help you identify which initiatives to prioritize so you can make the most impact.
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.
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