One standard light source for refractometers and polarimeters is the yellow light (D-line) from a sodium vapor lamp. Recently, there is an increasing use of interference filters on halogen lamps and LEDs to transmit the D-line.
The D-line from sodium vapor lamps is often thought of as one bright line, but it is actually emitted as two bright lines, D1 (589.6 nm) and D2 (589.0 nm). A D-line is comprised of both the D1 and D2 bright lines. From a numerical point of view, 589.3 is the midpoint of 589.0 and 589.6. As for the light intensity ratio, D2 has a stronger intensity, and the midpoint of the intensity is between 589.3 and 589.6.
For ICUMSA, the D-line wavelength is expressed as 589 nm or 589.3 nm for refractometers and 589.4400 nm for polarimeters. (The values found in the revision history and surrounding text are assumed to be in vacuum. In the air the D-line wavelength is 589.29 nm.)
According to the Japanese Industrial Standards (JIS), the D-line for refractometer and polarimeter standard light sources is 589.3 nm (for example, K0062 Test Methods for Refractive Index of Chemical Products and K0063 Test Methods for Optical Rotation of Chemical Products).
The Japanese Pharmacopeia's standard light source for both refractometers and polarimeters is D-line, but it does not reference a wavelength.
ATAGO uses 589 nm for the D-line in its catalogs and instruction manuals.
※ ICUMSA refers to observation tubes as "saccharimeter tubes." It can also be called a "cell" ("measurement cell"), regardless of industry.
※ α589.4400 nm refers to an angle of rotation with a wavelength of 589.4400 nm in a vacuum.
※ A 1 nm difference in wavelength in 26 g/100 mL liquid sucrose with a wavelength of between 587.0000 nm and 589.4400 nm causes an approximate change in angle of rotation of 0.126°.
※ Changes in angle of rotation due to a change in wavelength vary greatly depending on the substance that is being measured. The degree of change for each wavelength also varies greatly, so care must be taken when measuring. JIS can be a good reference.
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