Correct an observed refractive index to 20 °C or another reference temperature with a typical or custom correction factor, or estimate the factor.

20 °C is the usual standard (nD20). Change it if your reference is 25 °C or another value.

Positive when refractive index decreases as temperature rises.

Optional settings

Refractive Index Correction Formula

The following formula is used to calculate the corrected refractive index:

nDc = nDo + CF × (Tobs - Tstd)

Variables:

  • nDc is the corrected refractive index (corrected to the standard temperature)
  • nDo is the observed refractive index
  • CF is the refractive-index temperature correction factor (per °C). It is often positive for many liquids and corresponds approximately to -dn/dT.
  • Tobs is the observed temperature (°C)
  • Tstd is the standard/reference temperature (°C)

To calculate the corrected refractive index, add the product of the correction factor and the difference between the observed temperature and the standard temperature to the observed refractive index.

What is Refractive Index Correction?

Refractive index correction is the process of adjusting the measured refractive index of a substance to account for temperature differences from a standard reference temperature. Since the refractive index can vary with temperature, it is important to correct it to a standard temperature to compare measurements at a reference temperature. A linear correction is only an approximation over a validated range and does not establish measurement accuracy.

How to Calculate Corrected Refractive Index?

The following steps outline how to calculate the corrected refractive index:

  1. First, determine the observed refractive index (nDo).
  2. Next, determine the observed temperature (Tobs) in degrees Celsius.
  3. Next, determine the standard temperature (Tstd) in degrees Celsius.
  4. Next, determine the correction factor (CF) per degree Celsius.
  5. Use the formula nDc = nDo + CF * (Tobs - Tstd) to calculate the corrected refractive index (nDc).
  6. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Observed refractive index (nDo) = 1.3330

Observed temperature (Tobs) = 25°C

Standard temperature (Tstd) = 20°C

Illustrative correction factor (CF) = 0.00045 per °C; use a substance-specific validated coefficient. This example gives nDc = 1.3330 + 0.00045 × (25 − 20) = 1.33525