What is a Lumen?

A lumen is a unit of standard measurement used to describe how much light is contained in a certain area. The lumen is part of a group of standard measurements known as the photometry group, which measure different aspects of light. This group also includes such units as the candela, which measures luminance, and the lux, which measures illuminance. Strictly speaking, a lumen is defined as one candela multiplied by one steradian, which can be expressed as: 1(lm) = 1(cd) x 1(sr). A related unit of measurement — although not part of the standard units — is the foot-candle, which is often used in photography and film. To really understand what a lumen is, it is important to understand these units: the candela, the foot-candle, the steradian, and the lux. Although not entirely necessary to understand the lumen, there is an important distinction to be made between measures of radiance and measures of illuminance. When measuring radiance, you are basically looking at how much energy a ...  more

Never heard of Candlewatt. I have heard of Candlepower and from it Candella. If a light source emits one candela of luminous intensity uniformly across a solid angle of one steradian, its total luminous flux emitted into that angle is one lumen. Alternatively, an isotropic one-candela light source emits a total luminous flux of exactly 4π lumens. The lumen can be thought of casually as a measure of the total "amount" of visible light in some defined beam or angle, or emitted from some source. A standard North American 100 watt incandescent light bulb emits approximately 1700 lumens, while a 100 watt sodium vapor lamp emits around 15,000 lumens, about 9 times as much.  more

A. A lumen is a measurement of light. In simpler terms one lumen is equal to the amount of light that 1 candle will emit on 1 square foot, 1 foot away from the flame. 1 lumen = 1 foot candle Back To Top • Q. What is Lux mean? A. Lux is the metric unit equal to the amount of light falling on one square meter 1 lumen = 10 lux A lux is only 1 / 10 th of a lumen Back To Top • Q. What is the average lumen per watt ratio of an HPS and MH? A. HPS - 140,000 lumens per watt MH - 100,000 lumens per watt Fluorescent - 83,000 lumens per watt Mercury Vapor - 63,000 lumens per watt Incandescent - 17,500 lumens per watt Back To Top • Q. What is the definition of PAR? A. PAR stands for Photosynthetically Active Radiation Back To Top • Q. What is the PAR value? A. PAR value is the amount of light usable by the plants Back To Top • Q. When the lights are off what's going on with my plants? Obviously they don't just sleep so what do they do? A. In the dark cycle the plant shifts its focus from leaf ...  more