This LED Ring Light offers added illumination for examining stones and jewelry with amicroscope. It attaches easily to the head with 3 locking thumbscrews. There are 4 quadrantsof light that can each be turned on separately or in unison. When all 4 quadrants are onthere is a 7 stage variable light regulation from dim to bright with the ultimate brightnessbeing 6400 Kelvin. The inner diameter of the ring light is 60mm.