Information about Luminous Flux
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In photometry, luminous flux or luminous power is the measure of the perceived power of light. It differs from radiant flux, the measure of the total power of light emitted, in that luminous flux is adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light.
Units
The SI unit of luminous flux is the lumen (lm). One lumen is defined as the luminous flux of light produced by a light source that emits one candela of luminous intensity over a solid angle of one steradian. In other systems of units, luminous flux may have units of power.Weighting
The luminous flux accounts for the sensitivity of the eye by weighting the power at each wavelength with the luminosity function, which represents the eye's response to different wavelengths. The luminous flux is a weighted sum of the power at all wavelengths in the visible band. Light outside the visible band does not contribute. The ratio of the total luminous flux to the radiant flux is called the luminous efficacy.Contexts
Luminous flux is often used as an objective measure of the useful power emitted by a light source, and is typically reported on the packaging for light bulbs, although it is not always prominent. Energy conscious consumers commonly compare the luminous flux of different light bulbs since it provides an estimate of the apparent amount of light the bulb will produce, and is useful when comparing the luminous efficacy of incandescent and compact fluorescent bulbs.Luminous flux is not used to compare brightness, as this is a subjective perception which varies according to the distance from the light source.
| Quantity | Symbol | SI unit | Abbr. | Notes |
|---|---|---|---|---|
| Luminous energy | Qv | lumen second | lms | units are sometimes called talbots |
| Luminous flux | F | lumen (= cdsr) | lm | also called luminous power |
| Luminous intensity | Iv | candela (= lm/sr) | cd | an SI base unit |
| Luminance | Lv | candela per square metre | cdm–2 | units are sometimes called nits |
| Illuminance | Ev | lux (= lmm–2) | lx | Used for light on a surface |
| Luminous emittance | Mv | lux (= lmm–2) | lx | Used for light emitted from a surface |
| Luminous efficacy | lumen per watt | lm/W | ratio of luminous flux to radiant flux; maximum possible is 683.002 |
Photometry is the science of measurement of light, in terms of its perceived brightness to the human eye. It is distinct from radiometry, which is the science of measurement of light in terms of absolute power; rather, in photometry, the radiant power at each wavelength is
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Light is electromagnetic radiation of a wavelength that is visible to the eye (visible light). In a scientific context, the word "light" is sometimes used to refer to the entire electromagnetic spectrum.
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In radiometry, radiant flux or radiant power is the measure of the total power of electromagnetic radiation (including visible light). The power may be the total emitted from a source, or the total landing on a particular surface.
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Eyes are organs of vision that detect light. Different kinds of light-sensitive organs are found in a variety of organisms. The simplest eyes do nothing but detect whether the surroundings are light or dark, while more complex eyes can distinguish shapes and colors.
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In physics, wavelength is the distance between repeating units of a propagating wave of a given frequency. It is commonly designated by the Greek letter lambda (λ). Examples of wave-like phenonomena are light, water waves, and sound waves.
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Si, si, or SI may refer to (all SI unless otherwise stated):
In language:
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In language:
- One of two Italian words:
- sì (accented) for "yes"
- si
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For other uses of the word, see .
The lumen (symbol: lm) is the SI unit of luminous flux, a measure of the perceived power of light.
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candela (symbol: cd) is the SI base unit of luminous intensity (that is, power emitted by a light source in a particular direction, with wavelengths weighted by the luminosity function, a standardized model of the sensitivity of the human eye).
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In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction, based on the luminosity function, a standardized model of the sensitivity of the human eye.
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The steradian (symbol: sr) is the SI unit of solid angle. It is used to describe two-dimensional angular spans in three-dimensional space, analogous to the way in which the radian describes angles in a plane.
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In physics, power (symbol: P) is the rate at which work is performed or energy is transmitted, or the amount of energy required or expended for a given unit of time.
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weighting involves emphasising some aspects of a phenomenon, or of a set of data — giving them 'more weight' in the final effect or result. It is analogous to the practice of adding extra weight to one side of a pair of scales to favour a buyer or seller.
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luminosity function describes the average sensitivity of the human eye to light of different wavelengths. It should not be considered perfectly accurate in every case, but it is a very good representation of human eye sensitivity and it is valuable as a baseline for experimental
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A weight function is a mathematical device used when performing a sum, integral, or average in order to give some elements more of a "weight" than others. They occur frequently in statistics and analysis, and are closely related to the concept of a measure.
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Luminous efficacy is a property of light sources, which indicates what portion of the emitted electromagnetic radiation is usable for human vision. It is the ratio of emitted luminous flux to radiant flux.
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lamp, in technical usage, is a replaceable component such as an incandescent light bulb, which is designed to produce light from electricity. These components usually have a ceramic or metal base, which makes an electrical connection in the socket of a light fixture.
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Luminous efficacy is a property of light sources, which indicates what portion of the emitted electromagnetic radiation is usable for human vision. It is the ratio of emitted luminous flux to radiant flux.
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incandescent light bulb (also spelled lightbulb) or incandescent lamp is a source of artificial light that works by incandescence. An electrical current passes through a thin filament, heating it until it produces light.
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compact fluorescent lamp (CFL), also known as a compact fluorescent light bulb is a type of fluorescent lamp designed to replace an incandescent lamp. Many CFLs can fit in the existing incandescent light fixtures.
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Brightness is an attribute of visual perception in which a source appears to emit a given amount of light. In other words, brightness is the perception elicited by the luminance of a visual target. This is a subjective attribute/property of an object being observed.
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Si, si, or SI may refer to (all SI unless otherwise stated):
In language:
..... Click the link for more information.
In language:
- One of two Italian words:
- sì (accented) for "yes"
- si
..... Click the link for more information.
In photometry, luminous energy is the perceived energy of light. This is sometimes also called the quantity of light.
Luminous energy is not the same as the radiant energy, the corresponding objective physical quantity.
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Luminous energy is not the same as the radiant energy, the corresponding objective physical quantity.
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For other uses of the word, see .
The lumen (symbol: lm) is the SI unit of luminous flux, a measure of the perceived power of light.
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second (SI symbol: s), sometimes abbreviated sec., is the name of a unit of time, and is the International System of Units (SI) base unit of time.
SI prefixes are frequently combined with the word second to denote subdivisions of the second, e.g.
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SI prefixes are frequently combined with the word second to denote subdivisions of the second, e.g.
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For other uses of the word, see .
The lumen (symbol: lm) is the SI unit of luminous flux, a measure of the perceived power of light.
..... Click the link for more information.
second (SI symbol: s), sometimes abbreviated sec., is the name of a unit of time, and is the International System of Units (SI) base unit of time.
SI prefixes are frequently combined with the word second to denote subdivisions of the second, e.g.
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SI prefixes are frequently combined with the word second to denote subdivisions of the second, e.g.
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In photometry, the talbot (T) is a nonstandard unit of luminous energy, named in honor of the early photographer William Fox Talbot. It is exactly equal to the SI standard unit, the lumen · second:
SI photometry units
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- 1 T = 1 lm · s
SI photometry units
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For other uses of the word, see .
The lumen (symbol: lm) is the SI unit of luminous flux, a measure of the perceived power of light.
..... Click the link for more information.
candela (symbol: cd) is the SI base unit of luminous intensity (that is, power emitted by a light source in a particular direction, with wavelengths weighted by the luminosity function, a standardized model of the sensitivity of the human eye).
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The steradian (symbol: sr) is the SI unit of solid angle. It is used to describe two-dimensional angular spans in three-dimensional space, analogous to the way in which the radian describes angles in a plane.
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