What is the standard formula for percent transmittance in spectrophotometry?

• A. %T = Transmitted / Incident x 100
• B. %T = Incident / Transmitted x 100
• C. %T = Absorbance x 100
• D. %T = 100 - Transmitted

Answer: (A)

In spectrophotometry, percent transmittance tells you what fraction of the incoming light actually passes through the sample. The standard formula is %T = (I / I0) × 100, where I is the transmitted light intensity and I0 is the incident light intensity. This gives a value from 0 to 100%, indicating how transparent the sample is. Absorbance is related but a different quantity: A = -log10(%T/100) or A = log10(I0/I). The other forms mix up the numerator and denominator or use absorbance directly, or subtract from 100, none of which define percent transmittance.