Information about Luminosity Function
For the luminosity function in astronomy, see .
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The 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 purposes. It is a standard function established by the Commission Internationale de l'Éclairage (CIE) and may be used to convert radiant energy into luminous (i.e. visible) energy. It also forms the central color matching function in the CIE 1931 color space.
There are actually two luminosity functions in common use. For everyday light levels, the photopic luminosity function best approximates the response of the human eye. For low light levels, the response of the human eye changes, and the scotopic curve applies. The photopic curve is the CIE standard curve used in the CIE 1931 color space.
The luminous flux (or visible energy) in a light source is defined by the photopic luminosity function. The following equation calculates the total luminous flux in a source of light.
where
is the luminous flux in lumens,
is the power spectral density of the radiation, in watts per unit wavelength.
(also known as 
) is the standard luminosity function (which is dimensionless).
The standard luminosity function is normalized to a peak value of unity at 555 nm (see luminous coefficient). The value of the constant in front of the integral is usually rounded off to 683 lumens/watt. The small excess fractional value comes from the slight mismatch between the definition of the lumen and the peak of the luminosity function. The lumen is defined to be unity for a radiant energy of 1/683 watt at a frequency of 540x1012 Hz, which corresponds to a standard air wavelength of 555.016 nm rather than 555 nm, which is the peak of the luminosity curve. The value of
is 0.999997 at 555.016 nm, so that a value of 683/0.999997=683.002 is the multiplicative constant.[1]
The number 683 is connected to the definition of the candela (cd), the unit of the luminosity function, adopted in 1946 for the measurement of light intensity.
Improvements to the standard
The CIE 1931 color-matching functions, which include the CIE 1924 photopic
luminosity function as the y function, have long been acknowledged to underestimate the contribution of the blue end of the spectrum to perceived luminance. There have been numerous attempts to improve the standard function, to make it more representative of human vision[5]. Judd in 1951, improved by Vos in 1978, resulted in a function known as CIE 
. More recently, Sharpe, Stockman, Jagla & Jägle (2005) developed a function consistent with the Stockman & Sharpe cone fundamentals.[6] These curves are plotted in the figure above.
Scotopic luminosity
For very low levels of intensity (scotopic vision), the sensitivity of the eye is mediated by rods, not cones, and shifts toward the violet, peaking around 507 nm for young eyes; the sensitivity is equivalent to 1699[2] or 1700[3] lm/W at this peak.The standard scotopic luminosity function or
was adopted by the CIE in 1951, based on measurements by Wald (1945) and by Crawford (1949).[7]
See also
References
1. ^ Wyszecki, Günter and Stiles, W.S. (2000). Color Science - Concepts and Methods, Quantitative Data and Formulae, 2nd edition, Wiley-Interscience. ISBN 0-471-39918-3.
2. ^ Kohei Narisada and Duco Schreuder (2004). Light Pollution Handbook. Springer. ISBN 140202665X.
3. ^ Casimer DeCusatis (1998). Handbook of Applied Photometry. Springer. ISBN 1563964163.
2. ^ Kohei Narisada and Duco Schreuder (2004). Light Pollution Handbook. Springer. ISBN 140202665X.
3. ^ Casimer DeCusatis (1998). Handbook of Applied Photometry. Springer. ISBN 1563964163.
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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International Commission on Illumination (usually known as the CIE for its French-language name Commission internationale de l'éclairage) is the international authority on light, illumination, color, and color spaces.
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CIE 1931 XYZ color space (also known as CIE 1931 color space), created by the International Commission on Illumination (CIE) in 1931.
The human eye has receptors (called cone cells) for short (S), middle (M), and long (L) wavelengths.
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The human eye has receptors (called cone cells) for short (S), middle (M), and long (L) wavelengths.
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Photopic vision is the vision of the eye under well-lit conditions. In humans and many animals, photopic vision allows color perception, mediated by cone cells.
Photopic vision is the scientific term for human color vision under normal lighting conditions during the day.
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Photopic vision is the scientific term for human color vision under normal lighting conditions during the day.
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Scotopic vision is the monochromatic vision of the eye in dim light. Since cone cells are nonfunctional in low light, scotopic vision is produced exclusively through rod cells so therefore there is no colour perception.
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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
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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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In statistical signal processing and physics, the spectral density, power spectral density, or energy spectral density is a positive real function of a frequency variable associated with a stationary stochastic process, or a deterministic function of time, which has
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WATT
City of license Cadillac, Michigan
Broadcast area [1]
Branding NewsTalk 1240
First air date 1945
Frequency 1240 kHz
Format News-Talk-Sports
Power 1,000 watts
Class C
Owner MacDonald Garber Broadcasting
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City of license Cadillac, Michigan
Broadcast area [1]
Branding NewsTalk 1240
First air date 1945
Frequency 1240 kHz
Format News-Talk-Sports
Power 1,000 watts
Class C
Owner MacDonald Garber Broadcasting
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1 nanometre =
SI units
010−9 m 010−3 μm
US customary / Imperial units
010−9 ft 010−9 in
A nanometre (American spelling: nanometer, symbol nmSI units
010−9 m 010−3 μm
US customary / Imperial units
010−9 ft 010−9 in
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The luminous coefficient is a coefficient that measures the integrated fraction of the radiant power that contributes to its luminous properties as evaluated by means of the standard luminosity function.
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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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Scotopic vision is the monochromatic vision of the eye in dim light. Since cone cells are nonfunctional in low light, scotopic vision is produced exclusively through rod cells so therefore there is no colour perception.
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As the name of a color, violet (named after the flower violet) is used in two senses: first, referring to the color of light at the short-wavelength end of the visible spectrum, approximately 380–420 nm when indigo is recognized, or more commonly 380–450 nm[1]
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Color vision is the capacity of an organism or machine to distinguish objects based on the wavelengths (or frequencies) of the light they reflect or emit. The nervous system derives color by comparing the responses to light from the several types of cone photoreceptors in the eye.
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