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Convert Y-Axis unit details

The convert Y-Axis command recalculates the intensity values of IR, NIR, RAMAN or UV/VIS spectra and corresponding 3D data and converts the values into one of the following units:

  • Absorbance units

  • Transmittance units

  • %Transmittance units

  • Kubelka Munk

  • Reflectance units
    Popular unit with NIR spectra.

  • Energy

  • Counts

Spectra with raw intensity units (e.g. energy or counts) may also be converted to transmittance or absorbance if a corresponding reference spectrum is available. The convert Y-Axis command offers an option to load a reference spectrum if the source spectrum is in a suitable format. Please review the section convert Y-axis unit in the chapter commands for further information.

By subsequent application of the command, the units will be toggled.


Absorption is a process in which incident radiated energy is retained without reflection or transmission on passing through a medium.

Absorbance values can be easily converted into transmittance, percent transmittance or reflectance values using the following equations:

Absorbance / transmittance conversion

Absorbance / reflectance conversion

Absorbance / % transmittance conversion



Absorbance value


Transmittance value


Percent transmittance value


Reflectance value


The ratio of transmitted energy to the amount of incident energy is called transmittance. Transmittance was formerly called transmission. Transmittance values can be easily derived from the formulas given above.

Percent transmittance

For some applications in optics it might be useful to see transmittance values as percent transmittance values. All intensities will be scaled to fit an interval between 0 and 100 percent transmittance.

Kubelka Munk

Mostly used with diffuse reflectance spectra. Kubelka-Munk units are calculated from the Kubelka-Munk equation.


The ratio of reflected energy to the amount of incident energy is called reflectance.