Light Performance is an immensely important factor in achieving good light reflective properties in a diamond. A stone having good light performance will always appear bright, reflecting light from preferred spheres or angles of light.
Light Performance - Angular Spectrum Evaluation Tool (ASET)
In 2005, AGS Laboratories introduced a tool called Angular Spectrum Evaluation Tool (ASET). This tool allows the viewer to visually perceive how efficiently, or inefficiently, a diamond is handling light. ASET provides a quick and easy way to demonstrate a diamond’s interaction with light by showing light return image patterns with greater details and identifying the angles [angular spectrum] from which the diamond is gathering light. This is done by producing a color coded image of the diamond using the colors red, green, blue, and black or white. Each color represents and measures light eminating from different spheres around the diamond that are then reflected back by it.
RED: Red light strikes the diamond from 45° through 75° to the table. It measures high angles and high intensity light return and captures the brightest light that makes the diamond most brilliant.
GREEN: Green light is a less bright light which reflects off from indirect angles. It strikes the diamond from the horizon (0°) to 45°. It measures lower angles and lower intensity light return.
BLUE: Blue light represents "obstruction" and contrast. It is the pattern of light and dark areas that the viewing eye finds pleasing. It is caused by light that could have entered the diamond but which is obstructed by the viewer’s head hence the reason it's also called "head shadow". It should be distributed in a balanced and symmetrical pattern. Some blue around the crown of a diamond can add contrast but too much blue under the table of a diamond can cause the diamond to appear dark and lifeless.
WHITE or BLACK: White or black light (depending upon the lighting environment used) represents light leakage. It is areas within the diamond where light is literally lost. There should be very little of this in the pattern image.
What ASET Can Tell You
- Light performance (optical efficiency)
- Physical symmetry
- Optical symmetry
- The cutter’s expertise
Each image is a unique thumbprint, but the main objective of an ASET image is to reveal a well cut diamond. How well a diamond is cut will translate in its ability to sparkle. What one wants to see in a diamond using the ASET image device are symmetrical patterns with lots of red, some blue, and some green. One does not want to see much white or black (leakage) in any specific area. In general, more red than green should be visible in the ASET image of a diamond especially in the center or under the table area of a diamond. An exception to this rule occurs with Round Brilliant Diamonds that may have a table reflection area in the very center that might appear red, green or a combination of both which is acceptable.
A diamond’s light performance has traditionally been described in relations to brilliance (brightness), fire (dispersion) and scintillation (sparkle). Brilliance or (brightness) refers to the total amount of light returning from the diamond, fire (dispersion) is the degree to which light is broken into spectral colors, and scintillation (sparkle) is a dynamic effect associated with movement of light. Recently, other descriptors have been added to enhance the consumer’s understanding of a diamonds visual properties and interaction with light they include: contrast and pattern which describe the arrangement of light and dark areas resulting from reflections and leakage which describes areas that do not reflect light back to the viewer. ASET images encompass all these descriptors and are reliable. We strongly believe in ASET analysis, as it is a direct measure and visual representation of the actual light performance of a diamond.