A vector of names useful for extracting subsets of angular
response data from the diffusers.lst object.
Usage
all_diffusers
cosine_diffusers
dome_diffusers
entrance_optics
sensor_optics
ic_optics
ideal_opticsFormat
An object of class character of length 18.
An object of class character of length 16.
An object of class character of length 2.
An object of class character of length 3.
An object of class character of length 9.
An object of class character of length 3.
An object of class character of length 3.
Details
Irradiance measurements require diffusers or sensors with a response
proportional to the cosine of the angle of light incidence, i.e., varying
between a maximum and zero over 180 degrees in 3D. In practice no real
diffusers achieve this over 180 degrees, and only the best ones approach
the expected response over an angle of 160 to 170 degrees. Such entrance
optics are described as cosine corrected and data for them can be extracted
from diffusers.lst using cosine_diffusers. The response
expected is given by the projected light exposed area under a collimated
beam:
\(A_\mathrm{p} = A_\mathrm{max} \times \cos(z)\)
where \(z\) is the angle of incidence relative to the normal to the plane
of the entrance optics or diffuser. For a horizontal sensor, \(z\) is the
zenith angle of the sun.
Hemispherical scalar irradiance (or hemispherical fluence rate) requires an
entrance optic with a response that varies with the angle of incidence
between a maximum and its half over 180 degrees in 3D. Such sensors or
diffusers are seldom available off-the-shelf. Data for them can be
extracted from diffusers.lst using dome_diffusers. The
response expected is given by the projected light exposed area under
collimated light:
\(A_\mathrm{p} = A_\mathrm{max} \times 0.5 \times (1 + \cos(z))\)
where \(z\) is the angle of incidence relative to the normal to the plane
of the entrance optics or diffuser.
Scalar irradiance (or fluence rate) measurements require a diffuser with response invariant over 360 degrees in 3D. Real sensors of this geometry have a blind spot as a fibre or a detector have to be attached to them. The response expected is given by the projected light exposed area under collimated light: \(A_\mathrm{p} = A_\mathrm{max} \times 1\) for all angles of incidence.
The angular response of ready-to-deploy broadband sensors can be extracted
from diffusers.lst by sensor_diffusers. With a few exceptions
these sensors are designed to measure irradiance.
The angular response of entrance optics suitable for use with spectrometers
can be extracted from diffusers.lst by entrance_optics.
The angular response of bare sensors sold as electronic components
including integrated circuits and photodiodes can be extracted from
diffusers.lst by ic_optics. In some cases they approximate
a cosine response except at high \(z\) angles. In other cases they have
a much narrower angle of view.
The angular response expected based on physical quantity definitions can be
extracted from diffusers.lst by ideal_optics. They have been
computed using the equations shown above.
Responses are expressed relative to that for the maximum projected as fractions of one.
See also
Data in diffusers.lst and function
angular_response().
Examples
all_diffusers
#> [1] "ams_TSL254R" "ams_TSL257" "analytik_jena_cosine"
#> [4] "bentham_D7" "bentham_D7_dome" "ideal_cosine"
#> [7] "ideal_dome" "ideal_sphere" "licor_R"
#> [10] "ocean_optics_4mm" "schreder_J1002" "Scintec"
#> [13] "sglux_TOCON" "sglux_uv_cosine" "sglux_uvi_cosine"
#> [16] "Solarlight_501" "vishay_VEML6075" "vital_BW20"