Infrared spectroscopy is the spectroscopy that deals with the infrared region of the electromagnetic spectrum, that is light with a longer wavelength and lower frequency than visible light. It covers a range of techniques, mostly based on absorption spectroscopy.
Experimental film by Infrared spectroscopy each sample graph in a third example. Example 3 have the % Transmittance at 0.1%,example 6 have the % Transmittance at 0.1%,And unknown sample the % Transmittance at 10%.So,samples with low %T will be able to prevent a lot of light ,because less light to pass through are samples 3,6. %T of the unknown sample lower,it easier to light pass.