A 100-square-foot living room that requires 10-20 foot-candles, for example, will require 1,000-2,000 lumens. A 100-square-foot dining area that requires 30-40 foot candles will require 3,000-4,000 lumens. A small bedroom needs less than 10 foot candles and should use an energy-efficient lamp or light fixture instead of a candle.
Lumens are a way to quantify how much light can enter a space. The more lumens that fall on the surface you want to light, the more light it will receive. So if you have a large area to illuminate, more lumens are needed.
The amount of light required by any object or surface depends on how far it is from the source. Objects closer to the light will get brighter, while those farther away will appear darker. This is true even with high-quality lamps and lighting fixtures. The further away objects are from the light, the more lumens they need to receive before they are satisfied with the level of illumination.
For example, if you were to put a book on your desk and then turn off the main light above it, the book would still be well-lit because it's close enough to the lamp to receive some light. But if you moved the book to another part of the room where there was no light from the lamp, it would be very dark.
Determine the number of lumens required. A lumen is a unit of light measurement. To get the required lumens, multiply your room square footage by your room foot-candle requirement. Ceiling fixtures range from 10-60 watts per fixture, so you'll need from one to six bulbs depending on how much light you want to provide.
The average person needs about 150 lux (lux is a measure of illumination, similar to the more familiar term "fade level") of visible light to function properly. In other words, you need about 150 lux to be able to see what you're doing. Outside, sunlight is usually around 1000-10,000 lux, so as not to cause glare or harm your eyes. Incandescent lamps are about 3-5 lux, while fluorescent tubes are about 10,000-20,000 lux. LED lights are closer to 300-500 lux.
At night, when you can't use natural light, you need artificial lighting to get by. And at that time, it doesn't matter if it's 300 lux from an LED lamp or 3000 lux from the moon, you still need the same amount of lumens to be able to see clearly. So for nighttime reading, for example, you would need about 150-300 lux from an LED lamp.
As a general guideline, a sitting room or bedroom will require 10-20 lumens per square foot of lighting, but a bathroom or kitchen will demand 70-80 lumens per square foot of illumination. Simply multiply the square footage of the room by this amount to calculate the lumens required. For example, a room that's 100 square feet would need 1000 lumens of light.
The average person spends about two-thirds of their day in darkness, so it's important that we give our rooms adequate lighting. The amount of light needed depends on what you use the space for and how often you use it. For example, if you spend most of your time reading or watching television, then you will want to make sure there is enough light to see what you are doing. If you go into another room occasionally to visit with friends, you won't need as much light as someone who walks through their home every day.
Some people think that only the sun needs sunlight, others think trees need daylight too. Actually, everything from plants to animals need sunlight to survive and grow. Sunlight is actually made up of waves called "photons" that contain energy which can be converted into other forms of energy. Plants use the sunlight photons to make food, and animals use them to power their muscles and think things like "I must find food." Without sunlight, life would not be possible on earth!
To calculate the square footage of a room, multiply its length by its breadth. If the space is 10 feet wide and 10 feet long, the square footage is 100 square feet. A foot-candle is the amount of light that can be seen one foot distant from the source. So, if there are three foot-candles in a room, it will also be dark at a distance of three feet.
One candle gives off about 1/8 of an inch of daylight per hour. Three candles give off about 1/4 of an inch of daylight per hour. Seven candles give off almost 3/4 of an inch of daylight per hour. That's enough to read by!
So, to calculate the number of foot candles in a room, divide the output of several lamps by eight. For example, if two 40-watt lamps produce 15 inches of daylight between them, then the room is lit by 30 foot candles.
The maximum number of foot candles an average-sized room can hold without causing discomfort is 50. After that, people have to turn on more lights to avoid darkness.
The minimum number of foot candles required for comfortable reading is about 2.5. At this level, enough light enters through windows or other openings to allow you to read without straining your eyes.
To heat a room, 20 candles are required. According to study, one candle has about 80W heating power. As a result, 20 candles are about comparable to one 1600W space heater. A combined candle heat source of 1600W can fully heat a space. The US Energy Information Administration reports that the average household uses 907 kWh of energy per year, so the above calculation is reasonable.
The main advantage of candle heating over other forms of heating is its low cost; a single candle costs about $3. However, it has several disadvantages including risk of fire and need for constant maintenance. Also, once the candle burns down, it takes time to get another one, so you will not be able to quickly adjust the temperature in your house.
So, considering all factors, 20 candles are enough to heat a room efficiently.
One lumen per square foot is equal to a foot-candle. This is a British unit of measurement. A lumen is measured by a square meter or a lux in the metric system. As a result, a foot-candle is about comparable to 10 lux, or 10.57 lux. Modern light bulbs range from about 15 millicandles to over 100 kilocandles; thus, they are many times more powerful than a standard candle.
A lumen is the average number of photons emitted per second by a pure black body at a temperature of 3000 K. It is also the minimum level of illumination required to read a digital display at arm's length. A human eye can detect objects in low-light conditions up to about 1/10th of a lumen. Above that, we need special lenses or cameras.
So, yes, one lumen is the same as one foot-candle and it is needed to read a digital display at arm's length. There are 10 foot-candles in a tungsten filament light bulb and 20 foot-candles in an Edison lamp. Before electricity, gas lights had much higher lumens because they used real wax instead of oil or gas, which are white hot and give off almost no light themselves.
There are different ways of measuring luminous flux, such as foot-laments, workable lamps, and manometers.