KEY TERMS
Lumens
Lumen output, also known as brightness or light output, is a measure of the total quantity of visible light emitted by a light source per unit of time, weighted according to the human eye’s sensitivity to wavelengths of light, the study of which is known as luminous efficiency function. The reference point: a standard 100-watt incandescent light bulb produces about 1,500 – 1,700 lumens.
Watts
Not a measure of brightness; instead, it’s a measure of how much electricity (or energy) a light bulb consumes to reach its claimed brightness. Each type of light source, LED, fluorescent, halogen or incandescent has a different lumen-per-watt ratio. Below we’re going to use lumens as a measurement to make sure we have enough light for a space.
Wattage Equivalence
Since we’ve conflated watts and lumens, it’s easier to talk about bulbs in terms of watts. So, if a 100-watt incandescent produces 1,500 lumens, and a 10-watt LED does the same, the 10-Watt LED may advertise “100-watt equivalent” on its label.
Efficacy
The number of lumens a bulb produces for each watt it consumes. The higher the number, the more efficient the bulb. For example, lighting products that have been designated with the ENERGY STAR label are deemed high efficacy, meaning they have been determined to deliver the same features while using less energy.
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.
Determine the Foot-candles by Room Type
A foot candle is how bright a light is one foot away from its source. Lighting requirements/needs vary depending on the type of room being lit. For example, a bathroom or kitchen will require more foot candles than a living room or bedroom.
Determine the Required Lumens
To determine the lumens needed, 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.