what is the relationship between percent transmittance and absorption

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what is the relationship between percent transmittance and absorption?

what is the relationship between percent transmittance and the color of solution?

Those terms have most meaning to me in terms of ultraviolet and visible light. Hopefully that is the meaning that you need.


Percent transmitance is the percent of light that goes through a sample.


So if the intensity of light getting to the sample is I0, and the intensity of light that makes it through is I, transmitance is the ratio I0/I expressed as a percent. If half of the light is absorbed and half is transmitted transmitance is 50%.


Absorbance is the logarithm of I/I0. If half of the light is absorbed, then the absorbance (A) measured is log2 = 0.301.


Usually we measure absorbance with a spectrophotometer, on light of a very narrow wavelength range. We may say we measure absorbance at 254 nanometers (254 nm) or at 280 nm.


Solutions and solvents may absorb more or less at various wavelength of ultraviolet (UV) light, but look transparent and colorless to us because we do not see ultraviolet light. With a UV spectrophotometer, or a UV detector to record UV spectra (graphs of absorbance as a function of wavelength), and/or measure UV light absorbed at a certain wavelength, we analyze a lot of materials.


When a solution absorb some light in the visible range, what gets through is only part of the mix of visible wavelengths that makes up white light. You see a color made up of the visible wavelengths that get through. Some of the compounds I analyze absorb some blue light beyond 330 nm, along with ultraviolet light, and their solutions appear yellow. Right now I am working on a compound that absorbs a lot at around 540 nm, and the solutions look like red wine.

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