photometric: convert illuminant spectra to photometric units
Description
Convert radiometric units of power to photometric units,
using the standard photometric weighting curve.
Actinometric units (number of photons) are converted to radiometric units (power of photons) on-the-fly.
Usage
## S3 method for class 'colorSpec':
photometric( x )
Arguments
x
a colorSpec object with type equal to 'light'
Value
photometric returns an Mx1 matrix, where M is the number of spectra in x.
The rownames are specnames(x), and the colnames are 'Y'.
In case of ERROR it returns NULL.
Details
The function computes the dot product of x with the
photopic responsivity spectrum y from xyz1931.1nm.
This product is an Mx1 matrix, where M is the number of spectra in x.
It is then multiplied by the CIE-standard coefficient of 683 lumen/watt and returned.
The 5 radiometric inputs and photometric outputs are:
lll{
radiant flux 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 [$candela*m^{-2} = nit$]
}
References
Poynton, Charles.
Digital Video and HD - Algorithms and Interfaces.
Morgan Kaufmann.
Second Edition. 2012.
Appendix B, pp. 573-580.