A:Key aspects of high-quality light are the color appearance of the light itself, which is described by its color coordinates but is often condensed (with significant loss of information) to correlated color temperature (CCT), and how the light affects the color appearance of objects, which is referred to as color fidelity. Color fidelity can be quantified using the color rendering index (CRI), or with one of several other recently developed metrics. LED light sources have demonstrated that they can achieve a wide range of color qualities, depending on the demands of the lighting application. However, to achieve high levels of color quality, there are typically cost and efficiency tradeoffs. In general, a minimum CRI of 80 is recommended for interior lighting, and LED products can readily achieve this performance. CRI of 90 or higher indicates excellent color fidelity; LEDs can also meet this threshold. CRI is far from a perfect metric and is especially poor at predicting the fidelity of saturated reds, for which the supplemental value R9 is often used. New metrics, such as the fidelity index (Rf) and the gamut index (Rg), which are described in IES TM-30-15, can provide a more comprehensive evaluation of color rendering.