Distribute integrated lux across a reference spectral shape.

lux is a single scalar; a spectrum has many degrees of freedom. This function takes a reference shape and rescales it so its photopic integral equals lx. The shape assumption must be supplied by the caller.

Usage

lux2irradiance(
  lx,
  spectrum,
  lambda = NULL,
  LEF = CIE1931,
  binwidth = NULL,
  integration = c("rectangle", "trapezoid")
)

Arguments

lx: Target illuminance in lux.
spectrum: Reference spectral shape. Either a data frame with columns lambda and irradiance, or a bare numeric vector (in which case lambda must be supplied separately).
lambda: Wavelength grid in nm. Required when spectrum is a bare vector; ignored when spectrum is a data frame.
LEF: Luminous efficiency function. Defaults to CIE1931.
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".

Value

Numeric vector of rescaled spectral irradiance (same length as the wavelength grid).

Examples

spec <- data.frame(lambda = CIE1931$lambda, irradiance = CIE1931$W)
irr  <- lux2irradiance(5000, spec)