photometric: convert illuminant spectra to photometric units

In colorSpec: Color Calculations with Emphasis on Spectral Data

convert illuminant spectra to photometric units

Description

Convert radiometric units of power or energy to photometric units, using 4 standard photometric weighting curves. Actinometric units (number of photons) are converted to radiometric units (energy of photons) on-the-fly.

Usage

## S3 method for class 'colorSpec'
photometric( x, photopic=683, scotopic=1700, multiplier=1 )

Arguments

x	a colorSpec object with type equal to 'light', and with M spectra
photopic	the conversion factor for photopic vision, in lumen/watt. The CIE standard is 683, and another common value is 683.002.
scotopic	the conversion factor for scotopic vision, in lumen/watt. The CIE standard is 1700, and another common value is 1700.06.
multiplier	an conversion factor intended for conversion of units, and applied to both photopic and scotopic vision. For example if the input unit of x is watt*sr^{-1}, and the desired output unit is candlepower, then set multiplier=1/0.981.

Details

The function computes the product of x with luminsivity.1nm. This product is an Mx4 matrix, where M is the number of spectra in x. There are 3 columns for photopic vision, and 1 column for scotopic vision. These columns are multiplied by the appropriate conversion factors and the resulting Mx4 matrix is returned.

The 5 power-based input quantities and corresponding photometric outputs are:

radiant power [watt]	--->	luminous flux [lumen]
irradiance [watt*m^{-2}]	--->	illuminance [lumen*m^{-2} = lux]
radiant exitance [watt*m^{-2}]	--->	luminous exitance [lumen*m^{-2} = lux]
radiant intensity [watt*sr^{-1}]	--->	luminous intensity [lumen*sr^{-1} = candela]
radiance [watt*sr^-1*m^{-2}]	--->	luminance [candela*m^{-2} = nit]

The 2 common energy-based input quantities and corresponding photometric outputs are:

radiant energy [joule]	--->	luminous energy [talbot = lumen-second]
radiant exposure [joule*m^{-2}]	--->	luminous exposure [talbot*m^{-2} = lux-second]

and there are 3 more obtained by integrating over time. For example "time-integrated radiance" —> "time integrated luminance". But I have not been able to find names for these 3. The talbot is the unofficial name for a lumen-second.

Value

photometric() returns an Mx4 matrix, where M is the number of spectra in x. The rownames are specnames(x), and the colnames are specnames(luminsivity.1nm).
In case of ERROR it returns NULL.

Note

To get the right output quantity and units, the user must know the input quantity and units. If the units are different than those in the above list, then set multiplier appropriately.
It is up to the user to determine whether photopic or scotopic vision (or neither) is appropriate. The intermediate mesopic vision is currently a subject of research by the CIE, and might be added to this function in the future.

References

Poynton, Charles. Digital Video and HD - Algorithms and Interfaces. Morgan Kaufmann. Second Edition. 2012. Appendix B, pp. 573-580.

See Also

quantity, type, luminsivity.1nm, radiometric

Examples

photometric( solar.irradiance )  # unit is watt*m^{-2}

#             photopic1924 scotopic1951 photopic1978 photopic2008  # units are lux
# AirMass.0      133100.41     313883.2    133843.65     140740.3
# GlobalTilt     109494.88     250051.5    110030.31     115650.0
# AirMass.1.5     97142.25     215837.1     97571.57     102513.7

colorSpec documentation built on May 29, 2024, 6 a.m.