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Compute scotopic illuminance (V'(lambda) weighting).

Source: R/converters.R
scotopic_lux.Rd

Drop-in replacement for irradiance2lux using the CIE 1951 scotopic luminous efficiency function V'(lambda). The scotopic luminous efficacy K_m' = 1700 lm/W replaces the photopic K_m = 683 lm/W.

Usage

scotopic_lux(irradiance, ...)

# Default S3 method
scotopic_lux(irradiance, ...)

# S3 method for class 'numeric'
scotopic_lux(
  irradiance,
  lambda,
  photonic = FALSE,
  molar_unit = "photons",
  total = TRUE,
  binwidth = NULL,
  integration = c("rectangle", "trapezoid"),
  verbose = FALSE,
  ...
)

# S3 method for class 'lux_spectrum'
scotopic_lux(
  irradiance,
  total = TRUE,
  integration = c("rectangle", "trapezoid"),
  verbose = FALSE,
  ...
)

Arguments

irradiance

Spectral irradiance (W/m^2/nm or photons/m^2/s/nm) at each wavelength bin, or a lux_spectrum object whose quantity is "irradiance". Photonic lux_spectrum inputs are converted to energy units before photometric integration; radiance and reflectance spectra are rejected.

...

Ignored.

lambda

Wavelength in nm (not needed for lux_spectrum).

photonic

Logical; if TRUE, irradiance is in photon or molar units. Default FALSE.

molar_unit

Molar unit string when photonic = TRUE (e.g. "umol"). Default "photons".

total

Logical; sum per-bin values into a scalar. Default TRUE.

binwidth

Wavelength bin width in nm. Inferred from a regular multi-bin wavelength grid when NULL; required for a single bin under rectangular integration. Must be NULL for trapezoidal integration.

integration

Integration method passed to irradiance2lux: "rectangle" (default) or "trapezoid".

verbose

Logical; emit diagnostic messages. Default FALSE.

Value

A scalar scotopic lux value (when total = TRUE) or numeric vector.

Details

Scotopic illuminance uses the CIE 1951 scotopic luminous efficiency function \(V'(\lambda)\), which peaks at 507 nm. The maximum scotopic luminous efficacy is \(K_m' = 1700\) lm W\(^{-1}\): $$E_v' = 1700 \int_{380}^{780} E(\lambda)\,V'(\lambda)\,d\lambda$$ Computed internally by calling irradiance2lux with LEF = CIE_scotopic and applying the efficacy ratio \(1700/683\).

Note

The scotopic/photopic crossover occurs near 10 lx. Below that threshold — twilight, moonlight, deep water — scotopic readings better reflect perceived brightness.

Examples

data(Naples)
scotopic_lux(Naples$depth_10m, Naples$wv,
             photonic = TRUE, molar_unit = "umol")
#> [1] 40379.36