Preamble: SPD helps you avoid Melatonin Suppression
Spectral Power Distribution or 'SPD' is a plot of relative power at each wavelength distributed from a light source.
The Correlated Color Temperature or 'CCT' is a single value for degrees Kelvin (K) derived from averages of many wavelengths shown with SPD of that lighting.
Lighting can emit wavelength spikes undetected with a CCT value, but can affect ipRGC of the retina. CCT is rounded to fit name categories, therefore CCT for one group may be OK, and that same CCT of another group may not.
SPD is essential for that evaluation.
This LRC link has technical pages about SPD, and explains its need for color rendering index (CRI), full-spectrum index (FSI), full-spectrum color index (FSCI), correlated color temperature (CCT) and more.
This page you're on has a melatonin suppression predicting algorithm using the ratio between ≈ 450nm wavelength level to photopic wavelength levels. That ratio is derived with aid of Dr. Rea's lab test report and is applied to his Equation 1 for the degree of melatonin suppression from exposure to a light source.
The Nocturnal Melatonin Suppression test was not to evaluate Light Emitting Diodes (LEDs), the white LEDs helped to separate the 450nm wavelength in the ipRGC spectra.
The test results are based on the wavelength levels achieved by light-filtering, and show a 2:1 suppression difference between its derived Cool White to Warm White labels.
From this test, degree and threshold of melatonin suppression may now be predictable by using the LED SPDs.