Colour Rendering Index
If you have spent hours selecting paint colours, fabrics and carpets then the CRI of the lights you install must be high or you have probably wasted your time.
A CRI of 50 will give you the colour rendering of a sodium street lamp. Ideally you need a CRI of 90 or better. Most LED's have a CRI of 80 which is adequate but will not give exact natural colour.
The tradeoff is that high CRI of 90+ means less light output, so these lights use more power to compensate and are more expensive.