# Best way to calculate UV-Vis absorption onset?

## Homework Statement

Hello,
I have a bunch of UV-Vis spectra to analyze and I am having a hard time choosing what the "onset" of each spectrum is, which I will use to calculate the optical band gap of each spectrum.

## The Attempt at a Solution

I read somewhere that plotting wavelength vs. (wavelength*Absorbance)^2 and then fitting through the linear portion of the graph, where the intercept corresponds to the onset.
By calculating the first derivative and checking the zero point after the last saddle point could also yield the onset? thanks

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## Homework Statement

Hello,
I have a bunch of UV-Vis spectra to analyze and I am having a hard time choosing what the "onset" of each spectrum is, which I will use to calculate the optical band gap of each spectrum.

## The Attempt at a Solution

I read somewhere that plotting wavelength vs. (wavelength*Absorbance)^2 and then fitting through the linear portion of the graph, where the intercept corresponds to the onset.
By calculating the first derivative and checking the zero point after the last saddle point could also yield the onset? thanks
Tauc plots are typically used.