CRI (color reproduction index) is the measurement of how accurately a light source can reproduce colors. My question is: what gives a light a good CRI? What do manufacturers do to accomplish such thing?
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A good light source has a smooth continuous spectrum similar to a material that is heated to a high temperature like the sun. The reflectivity of surfaces is also distributed along the spectrum of light, with sharper peaks corresponding to more saturated, festive colors.
Our attempts at creating efficient light emitters through excitiation of gases like mercury vapor or with light diodes produce radiation in a narrow band of frequencies. For example, sodium lights along highways have a sharp orange color, which is determined by the configuration of electrons in the chemical. If an object’s color falls in the gaps between these narrow emission bands, it will appear darker. Under a sodium light blue objects appear black. LEDs are slightly better than gases, giving off a broader spectrum.
To improve the light quality, parts of a light bulb are coated with materials that get excited when hit by incoming photons and re-emit light of a lower wavelength. Good color resolving ability is obtained by mixing multiple phosphor materials in precise proportions.
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