Absorbance (optical density) from transmittance.

The negative logarithm of transmittance. Natural-log absorbance (base = "e") is used by vision scientists and oceanographers; base-10 absorbance (base = "10") is "optical density" (OD), used by chemists and filter makers. They differ by a constant: \(OD = A\log_{10}e \approx 0.4343\,A\) (Johnsen 2012, ch. 4).

Usage

absorbance(transmittance, base = c("e", "10"))

Arguments

transmittance

Transmittance (0-1]. Vectorised.

base

"e" (natural-log absorbance, default) or "10" (optical density).

Value

Absorbance / optical density (dimensionless, \(\geq 0\)).

References

Johnsen S (2012) The Optics of Life. Princeton University Press, ch. 4.

See also

transmittance

Examples

absorbance(0.01, base = "10")   # OD = 2 (1% transmitted)
#> [1] 2
absorbance(exp(-1.5))           # natural-log absorbance = 1.5
#> [1] 1.5