How to Calculate the Percent Transmittance

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How to Calculate the Percent Transmittance
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The per cent transmittance reflects the amount of light that passes through a sample. Absorbance is the quantity of light that the sample absorbs. Higher absorbance corresponds to lower transmittance. You can easily measure absorbance on any spectrophotometer instrument. Absorbance and the per cent transmittance are related by the following equation: Absorbance = -log (per cent transmittance/100).

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  1. 1

    Measure or find out the absorbance value for your sample. For example, the absorbance is 0.532.

  2. 2

    Multiply the absorbance by -1 to calculate the negative value. In this example, the negative absorbance is 0.532 x (-1) = -0.532.

  3. 3

    Raise 10 to the power of the negative absorbance. In this example, 10^(-0.532) = 0.2938.

  4. 4

    Multiply the value from Step 3 by 100 to calculate the per cent transmittance. In this example, the per cent transmittance is 0.2938 x 100 = 29.38 per cent.

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