Lumen

The lumen (symbol: lm) is the International System of Measurement unit for measuring luminous flux, a measure of the light power emitted by the source. The luminous flux differs from the radiant flux in that the former contemplates the variable sensitivity of the human eye to different wavelengths of light and the latter involves all the electromagnetic radiation emitted by the source according to Wien's and Stefan-Boltzmann's laws. regardless of whether such radiation is visible or not.

The lumen is defined in its relation to the unit of luminous intensity, the candela (cd) and the unit of solid angle, the steradian (sr) thus:

${displaystyle {rm {1;lm=1;cdcdot sr}}}}$

Explanation

If a light source emits one candela of luminous intensity uniformly at a solid angle of one steradian, its total luminous flux emitted at that angle is one lumen. Alternatively, a one candela intensity isotropic light source emits a total luminous flux of exactly 4π lumens (≈12.56 lm). Lumen can be interpreted less rigorously as a measure of the total "amount" of light visible at a given angle, or emitted from a given source. In turn, when a lumen falls on a surface of 1 m², it is said that said surface has an illumination of one lux.

A 100-watt incandescent bulb emits approximately 1,000 lumens, while a sodium vapor lamp of the same power emits around 12,000 lumens, about twelve times more, and can emit up to 20 times more than an incandescent lamp, depending on the type of lamp.

Similarly, if you want to know the power needed to illuminate a surface with a certain light level, you must consider that:

(1 lux @ 555 nm = 1/683 W/m2)

For example, if you want to illuminate a rectangle of a soccer field (100x50 m) with a brightness equivalent to a clear day (about 100,000 lux; see daylight), the light output required (expressed in kilowatts) must be:

W = (100.000 lux · 1/683 (W/m2·lux) · 100 m · 50 m /1 000 = 732 kW

Electricity consumption, depending on the performance of the type of bulbs used, will be even higher.

Electric lighting

A standard LED lamp that produces 470 lumens. It consists of about the sixth part of the energy of its incandescent equivalent producing the same luminosity.

Lamps used for lighting are often labeled with their light output in lumens; in many jurisdictions this is required by law.

A 23W spiral compact fluorescent lamp, for example, emits approximately 1,400 to 1,600lm. Many compact fluorescent lamps and other alternative light sources are labeled as being equivalent to an incandescent bulb with a specific wattage. Below is a table showing the typical luminous flux of common incandescent bulbs and their equivalents for different types of lamps.

On September 1, 2010, European Union legislation came into effect that requires lighting equipment to be labeled primarily in terms of luminous flux (lm), rather than electrical power output. This change is a result of the European Union's Ecodesign Directive for Energy Using Products (EuP). For example, under the European Union standard, an energy efficient light bulb purporting to be the equivalent of a 60 W tungsten bulb must have a minimum light output of 700-750 lm.

Power of a projector

ANSI Lumen

The light output of a projector is often measured in lumens. The American National Standards Institute (ANSI) has created a standard for determining light output by taking measurements at different positions and calculating an average value. On the commercial side, light output calculated using this method is often referred to as publish in "ANSI lumen", to distinguish them from fixtures whose wattage has been calculated in some other way. ANSI lumen measurements are generally more accurate than those offered by other projector industry techniques.

Peak Lumens

Peak lumens are a measure of light output commonly used for CRT projectors. Its measurement is made using a pattern with 10% to 20% of the image in white (in the center), and the rest in black. The luminous power is measured in the central area. The technical limitations of these types of projectors mean that they produce the greatest brightness when only a small area is illuminated, as in this test. The result is that one fixture can produce 1,200 peak lumens, and only 200 ANSI lumens.

International System Photometry Units