SC2 is a dome model with a ring of light that peaks at 45° elevation. It is dark overhead and at the horizon.
In more detail
Of our three dome models, it is the closest to the light on a stone on a hand. The definition follows Robert W. Strickland's GemRay user guide; the implementation is our own.
How we measure it
In the Brightness & Tilt Analysis, W = 2 sin e cos e for elevation e. W is 0 inside the head shadow and below the horizon.
Related terms
- Dome model: A dome model is an idealized light source: a dome over the stone that weights light by its elevation. Our Brightness & Tilt Analysis uses three dome models: ISO, COS and SC2.
- ISO lighting: ISO is a dome model that lights the stone evenly from every direction above the horizon. It asks only how much light comes back, not from where.
- COS lighting: COS is a dome model in which light is brightest overhead and fades to zero at the horizon. Each direction is weighted by the sine of its elevation.
- Brightness & Tilt Analysis: The Brightness & Tilt Analysis is a free Digital Gemology tool. It measures how much dome light a cut returns face-up, and how this changes with tilt.