Light, in GIA fancy-colour diamond grading nomenclature, is one of the saturation grades within the fancy-colour scale for yellow and brown diamonds. The full scale, from lowest to highest saturation, runs Faint, Very Light, Light, Fancy Light, Fancy, Fancy Intense, Fancy Vivid and Fancy Deep, with the Fancy Dark grade applied separately to dark brown stones. A Light Yellow or Light Brown diamond falls below the Fancy Light threshold and is consequently outside the formal Fancy Colour bracket.

The distinction matters commercially. A Light Yellow diamond is graded on the same colour scale as a colourless white diamond beyond the Z grade, and is priced accordingly: typically as a coloured stone of lesser intensity, well below the per-carat values that begin at Fancy Light and rise through the higher grades. A retailer marketing a Light Yellow or Light Brown stone as a Fancy Yellow or Fancy Brown is misrepresenting the GIA grade and the price tier.

Light grades are most often encountered in cape-series yellow stones, in which case the colour reflects natural nitrogen impurities at low concentrations, and in light brown stones from a range of sources. Treated stones can also fall in the Light range when the treatment imparts only a modest colour shift; identification of treatment is independent of the grade itself and should be checked against laboratory documentation.