Radiance, Brightness, Sparkle
noun
If 輝く is "to shine" or "to glitter" think about the noun version of this. This would be radiance. Radiance can come in the form of shining and glittering.
かがやき
The reading comes from 輝く.
私はそのダイヤモンドの輝きに目がくらんでしまいました。
I was disoriented by the radiance of the diamond.