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Topic: Spectral power distributions

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	NationMaster - Encyclopedia: Spectral power distribution
		The spectral power distribution (SPD) of a light source is a measurement of the energy output at points (usually 31) along the visible spectrum.
		In applied mathematics and physics, the spectral density, power spectral density, or energy spectral density is a general concept applied to a signal which may have physical dimensions such as power per Hz, or energy per Hz, or none at all.
		First, the SPD of an equal energy spectrum is, indeed, "full" across the entire visible spectrum and, second, an equal energy spectrum is neutral with regard to any prejudicial associations, positive or negative, with "natural" light sources.
	www.nationmaster.com /encyclopedia/Spectral-power-distribution (364 words)

	Spectral density - Definition, explanation
		The units of spectral power density are commonly expressed in watts per hertz (W/Hz) or watts per nanometer (W/nm) (for a measurement versus wavelength instead of frequency).
		The spectral centroid of a signal is the midpoint of its spectral density function, i.e.
		The power spectral density of a light source is a measure of the power carried by each frequency or "color" in a light source.
	www.calsky.com /lexikon/en/txt/s/sp/spectral_density.php (607 words)

	Speech Enhancement
		Hence, in the case of stationary noise, it suffices to subtract the mean noise power to obtain a least squares estimate of the power spectrum.
		Power spectral subtraction is a minimum mean square estimator with little or no assumptions about the prior distributions for power spectral values of speech and noise.
		Within the framework of spectral magnitude estimation two major improvements are: (i) modeling of realistic a priori statistical distributions of speech and noise spectral magnitude coefficients [EM84], (ii) minimizing the estimation error in a domain which is perceptually more relevant than the power spectral domain (e.g., log magnitude domain) [PB84,EM85,VC89].
	cslu.cse.ogi.edu /HLTsurvey/ch10node5.html (1257 words)

	Spectral density - Wikipedia, the free encyclopedia
		In applied mathematics and physics, the spectral density, power spectral density, or energy spectral density is a general concept applied to a signal which may have physical dimensions such as power per Hz, or energy per Hz, or none at all.
		The units of power spectral density are commonly expressed in watts per hertz (W/Hz) or watts per nanometer (W/nm) (for a measurement versus wavelength instead of frequency).
		The spectral density of f(t) and the autocorrelation of f(t) form a Fourier transform pair (for PSD versus ESD, different definitions of autocorrelation function are used).
	en.wikipedia.org /wiki/Spectral_power_distributions (1039 words)

	Light-emitting diode white light source - Patent 5851063
		The spectral distributions of actual LED's show that the core of the lineshape is well-approximated by a Gaussian, but the "wings" tend to be more intense than a Gaussian; in addition, there tends to be some asymmetry in the actual spectral distribution with more intensity on the longer wavelength side of the peak.
		The spectral linewidth of the LED is not an independent parameter.
		The efficacy is the photometric analog of the radiometric efficiency; i.e., the efficiency is the ratio of the visible power produced to the input electrical power, whereas the efficacy is the ratio of the integral of the visible power per unit wavelength weighted by the photopic eye response to the input electrical power.
	www.freepatentsonline.com /5851063.html (2201 words)

	Color Glossary
		The differences in spectral sensitivity among the photopigments found in the different types of human photoreceptors are due to differences in their opsins.
		Spectral power distribution (of a light) At each wavelength in the visible spectrum, the power of the light at that wavelength as a proportion of its total power over the visible spectrum.
		Spectral reflectance (of a surface) At each wavelength in the visible spectrum, the proportion of incident light the surface reflects at that wavelength.
	www.uic.edu /%7Ehilbert/Glossary.html (5536 words)

	How can full-spectrum light sources be compared? \| Full-Spectrum Light Sources \| Lighting Answers \| NLPIP
		Moreover, a daylight SPD is not particularly smooth and uniform depending upon atmospheric composition, particularly the amount of water vapor.
		First, the SPD of an equal energy spectrum is, indeed, "full" across the entire visible spectrum and, second, an equal energy spectrum is neutral with regard to any prejudicial associations, positive or negative, with "natural" light sources.
		The cumulative SPD for an equal energy spectrum is shown (blue) with the cumulative SPD of the example light source (green).
	www.lrc.rpi.edu /programs/NLPIP/lightingAnswers/fullSpectrum/comparisons.asp (1218 words)

	Synthesized lighting device - Patent 4963798
		For discussions relating to this invention, the median wavelength of the visual spectral distribution is hereby defined as the wavelength which divides the total radiant energy emitted from the synthesizer during a typical one second period of operation that is within the bandwidth between 380 and 740 nanometers in half.
		Also as the power is increased the intensity of the diode illumination increases approximately proportionally and this characteristic combined with their stable color reduces color changes in the synthesized light.
		As the power is reduced, the incandescent lamp 27 prevents the light emitting diode lamps 21, 22 from turning off by reducing its resistance and shifting a larger percentage of the total power consumed by the series circuit to the light emitting diode lamps 21, 22.
	www.freepatentsonline.com /4963798.html (4344 words)

	Color Glossary
		The differences in spectral sensitivity among the photopigments found in the different types of human photoreceptors are due to differences in their opsins.
		Spectral power distribution (of a light) At each wavelength in the visible spectrum, the power of the light at that wavelength as a proportion of its total power over the visible spectrum.
		Spectral reflectance (of a surface) At each wavelength in the visible spectrum, the proportion of incident light the surface reflects at that wavelength.
	tigger.uic.edu /~hilbert/Glossary.html (5536 words)

	Proposed Reference Solar Spectral Power Distributions for Miami and Phoenix From Three Years of Measurements \| Atlas - ...
		Scanning spectral radiometers were installed at exposure laboratories in Miami and Phoenix at a 45° angle from horizontal facing south throughout 1997, 1998 and 1999.
		Due to spectral scans being taken on a local standard time schedule rather than a solar time schedule, the data are properly denoted as "near solar noon".
		These SPDs are properly denoted as hemispherical solar spectral power distributions for a 45° south facing surface near solar noon in Miami and Phoenix.
	www.atlas-mts.com /en/client_education/weathering_library/proposed_reference_solar_spectral_power_distributions_for_miami_and_phoenix_from_three_years_of_measurements/index.shtml (1931 words)

	Spartanburg SC \| GoUpstate.com \| Spartanburg Herald-Journal
		Metamerism is the situation where two color samples with different spectral power distributions appear to be the same color when viewed side by side.
		A spectral power distribution describes the proportion of total light emitted, transmitted or reflected by a color sample at every visible wavelength; it precisely defines the light from any physical stimulus.
		In all cases, the proportion of long-wavelength-sensitive cones to medium-wavelength-sensitive cones in the retina, the profile of light sensitivity in each type of cone, and the amount of yellowing in the lens and macular pigment of the eye, differs from one person to the next.
	www.goupstate.com /apps/pbcs.dll/section?category=NEWS&template=wiki&text=Metamerism_(color) (1035 words)

	A computational analysis of colour constancy (Site not responding. Last check: )
		It is a Gaussian function of the spectral distance of the surface's spectral centroid from the lambda max of the cone photoreceptor.
		The power of the Crule algorithm derives from the fact that the gamut is both characteristic of the illuminant and invariant (as a limit) with changing scene content.
		These are the spectral centroid; the spectral curvature, which is related to spectral dispersion or bandwidth; and the value at the centroid, which is a maximum or a minimum depending on the sign of the spectral curvature.
	aardvark.ucsd.edu /color/macleod+golz.html (12834 words)

	Journal of Vision - Does human color constancy incorporate the statistical regularity of natural daylight?, by Delahunt ...
		(λ) is the spectral power distribution of the illuminant.
		Spectral measurements were made at 4-nm increments between 380 and 780 nm but interpolated with a cubic spline to the CIE-recommended wavelength sampling of 5-nm increments between 380 and 780 nm.
		The spectral power distribution of each phosphor was measured at a range of intensity levels to measure and correct for the nonlinear relation between digital input and light intensity output characteristic of CRT monitors.
	journalofvision.org /4/2/1/article.aspx (13345 words)

	Light and Color - Basic Color Theory for the Desktop - Technical Guides
		Light sources, whether actual sources or illuminants, are primarily characterized by their color temperature and spectral power distribution.
		Spectral power distribution refers to the wavelengths that make up the light emitted from a source or illuminant at a particular color temperature.
		Note how the florescent source is relatively low in terms of relative power as compared to CIE Source A (a tungsten-filament bulb) and average daylight and how it's relative power spikes sharply at certain wavelengths.
	phoenix.sce.fct.unl.pt /abacus/diversos/textos/adobe_color_theory/light.html (1330 words)

	[No title]
		The peak of the spectral distribution curve is at 9.8
		It is defined as the ratio of the radiant power emitted per area to the radiant power emitted by a flbody per area.
		) of a surface is the ratio of the radiant power absorbed to the radiant power incident on the surface.
	www.newport.com /Strahlungsgesetze/381843/1033/catalog.aspx (659 words)

	JAIC , Volume 39, Number 2, Article 4 (pp. to )
		The spectral power distribution for this type of illumination is characterized by a continuous, smooth curve throughout the visible spectrum, increasing toward the long-wavelength end.
		Consequently, this study was designed to relate the spectral power distribution of lighting to the responses of subjects viewing artworks in a simulated art gallery setting.
		The author's own studies of spectral power distributions found that, at equal illuminances (lux) and the same color temperature, the irradiance (W/m2) for a three-band source may be as much as 40% less than for an incandescent lamp.
	aic.stanford.edu /jaic/articles/jaic39-02-004_1.html (1460 words)

	An Investigation of Headlamp Glare, DOT HS 809 672, October 2003 (Site not responding. Last check: )
		This report describes research to investigate and quantify the impact of glare illuminance, glare spectral power distribution, and glare source size on peripheral detection of small targets in the field.
		Neither the spectral power distribution (halogen, high intensity discharge or blue-filtered halogen) nor glare source size (from 9 to 77 cm2 in area) affected peripheral detection, once the glare illuminance was held constant.
		Spectral power distribution also affected discomfort (even though it did not affect visual performance) with the high intensity discharge headlamps eliciting ratings of greater discomfort than the halogen and blue-filtered halogen headlamps, when the glare illuminance was held constant.
	www-nrd.nhtsa.dot.gov /departments/nrd-01/GlareSpectrum/pages/ExecSumm.html (369 words)

	oe magazine - test talk (Site not responding. Last check: )
		In the case of tristimulus colorimeters, the mismatch of the relative spectral responsivities of the individual channels to the CIE color-matching functions can be a source of error when the spectral distribution of the source under test differs from the calibration source.
		Be careful, however--these uncertainties are often for measurements of an incandescent source with a color temperature of approximately 2856 K. These sources approximate the spectral power distribution of CIE Standard Illuminant A, a common standard source used in photometry and colorimetry.
		If we measure an artifact with the same spectral distribution as the calibration source, measurement errors tend to be canceled out, and the uncertainty will be small.
	oemagazine.com /FromTheMagazine/feb02/testtalk.html (655 words)

	Labsphere
		The spectral power distribution of light emitted from a flbody is a function of its temperature only and is described by Planckâs law.
		The dark-adapted relative spectral response of the eye is called the spectral luminous efficiency function for scotopic vision, Vâ(l).The scotopic response was first adopted by CIE in 1951 and applies to the spectral region between 380 and 780nm, with a peak at 507nm.
		This quantity is used to evaluate the total power of light sources at given wavelengths, especially in UV and IR, or to determine the color of light sources.
	www.labsphere.com /glossary.aspx (4736 words)

	Energy
		The large differences in their various spectral distributions is not generally considered to be important, because photopic luminance (illuminance) is thought to be the primary attribute of the spectral distribution of the source with regards to visual performance.
		The lumen output is obtained by averaging the wavelength dependent spectral power distribution (SPD) of a lamp over the photopic visual efficiency of the eye [the V() function].
		This ratio is a property of the lamp spectral power distribution (SPD) and to the extent that this distribution is independent of lamp intensity (as is the case for most fluorescent lamps) the ratio will be a constant independent of lamp intensity.
	www.naturalux.com /Energy.htm (4924 words)

	What is Metamerism?
		Example: most people have experienced sample metamerism when putting on two socks that appeared to be fl while in the bedroom (which may have incandescent lights), but later finding that one is fl and the other is blue upon stepping into the kitchen (which may have fluorescent lights).
		The differences in the wavelength distribution between the incandescent and fluorescent lights interact with the differences in the spectral reflectance curves of the socks to make them appear the same in one light source and different in another.
		Illuminant metamerism: Illuminant metamerism is witnessed when you have a number of spectrally matched (exactly the same) samples, but when each is independently, yet simultaneously illuminated and viewed under lights whose spectral power distributions differ.
	www.wisegeek.com /what-is-metamerism.htm (689 words)

	Photo Research, Inc. - PR-705/PR-715 SpectraScan Systems
		Spectral measurements are made in near real-time as light passes through a measuring aperture, is dispersed by a diffraction grating and then imaged onto a multi-emlement detector.
		The PR-705 measures Spectral Power Distributions in the visible range from 380-780 nm and the PR-715 measures the visible/NIR range from 380-1068nm.
		Two powerful on-board microprocessors control the hardware and mathematically calculate photometric and colorimetric values for the acquired spectral data during a measurement.
	www.photoresearch.com /current/pr705.asp (721 words)

	LOGI: The modality level
		We will focus on spectral reflectance distributions, rather than spectral power distributions, because adaptively relevant objects that emit their own light are environmentally rare.
		Hence the physically constant property of most objects is the spectral reflectance distribution, which combines with the spectral power distribution of light impinging on the object to give rise to the spectral power distribution received by the human eye.
		The spectral reflectance distribution is defined over the wavelengths from 400nm to 700nm (the visible range), and since wavelength is a continuum, the spectral reflectance distribution can theoretically require an unlimited number of quantities to specify.
	www.singinst.org /LOGI/levels/modality.html (4402 words)

	Color temperature - Wikipedia, the free encyclopedia
		This index is useful in determining the suitability of illuminating spaces occupied by humans, since there are adverse health effects of over-illumination by artificial lights or by mismatch of natural light sources.
		The spectral power distributions provided by many manufacturers may have been produced using 10 nanometre increments or more on their spectroradiometer.
		The result is what would seem to be a smoother (fuller spectrum) power distribution than the lamp actually has.
	en.wikipedia.org /wiki/Color_temperature (2133 words)

	Color theory, colorspaces
		Initially, this is the same situation as depicted in the previous section (#3), except that we make it a point to choose pure spectral colors whose amplitude=1 points lie roughly on the red, green, and blue parts of the spectral locus.
		In terms of Thomas Young's matching experiment, the knob for one primary is set to its maximum at each of these points, and the other two knobs are set to zero.
		However, the gamut will always fall within the convex hull ("shrink-wrap") of the spectral locus, because that represents all the (normalized) responses possible in our visual system, and therefore the full range of colors we humans can see.
	graphics.stanford.edu /courses/cs248-04/color/color1.html (448 words)

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