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Properties of Light

Light is a type of energy that travels as a wave-particle. The wavelength of light is the distances between peaks in the waves as light travels. Wavelengths are measured in nanometers (nm) and different wavelengths of light represent differing colors. White light is a mixture of the visible light spectrum. Light of long wavelengths (infra-red) and very short wavelengths (ultra violet) are invisible to humans but can be observed by other organisms. As wavelength decreases, the energy of the light is increased.

Diffraction of light through a prism exposes the components wavelengths of light.

Spectrophotometry

Spectrophotometers (spectro-image/color ; photo-light ; meter-measure) are used for chemical analysis of solutions based on properties of absorption or transmission.

Schematic of a spectrophotometer. The monochromator is a prism that splits the light. A single wave-length of light is focused through the aperture to pass through the solution in the cuvette.

Transmittance refers to the amount of light that passes through the solution.

T=\frac{I}{I_0}

Transmittance of a light source through a cuvette. The intensity of light, I0, decreases as it passes through the solution. The light detected by the sensor, I, reflects the transmittance of the solution.

If light is being absorbed by chemicals in the solution, this results in a lower transmission. Absorbance is therefore inversely related to transmittance as expressed by the equation:

A=-\log_{10}T

Follow the virtual demonstration at  https://www.ncbionetwork.org/iet/spectrophotometer/ for a more in-depth explanation of spectrophotometry.

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