100% Light Return???

In trying to have the last word on the importance of the Cut in defining a diamond's appeal, many sellers promote magic numbers - like "100%" light return.

Buyers beware!

That notion is far too simplistic. I find that "light return" percentages are rather meaningless for many reasons. A mirror returns 100% of the light shined on it. Is it as beautiful as a diamond? Nope!

There are various methods used to measure so-called light return. Mostly it is done by “virtual modeling” of the diamond. These models are defined by exterior measurements of a stone which are then used to create a computer model, which in turn is subjected to light ray-tracing analysis (AGS and GIA and DiamCalc).

Others simply use only “face-up” lighting, pixel-counting methods and/or undefined numeric scales (Brilliant Scope and Isee2). But we already know that "100% light return" is definitely not the Holy Grail of diamond beauty - even if it were possible to achieve.

Ironically, the pictures that are offered as "proof" of 100% light return are a case in point. You should ask yourself why there are various shades of red/pink and black/grey and even white in these types of photos (Fire Scope and Ideal Scope).

Don't they actually highlight different and/or varying degrees of "light intensity"? How drastically will they change when the diamond is tilted to one side or the other - as is the reality in everyday usage?

The look of a diamond changes dramatically whenever the position of the diamond, the light and/or the observer is changed. It should be easy to understand that viewing a diamond exactly perpendicular to its table is only a rarefied or "special" case. What do you suppose happens to the picture whenever you view a diamond from any other angle?

One thing everyone knows for sure, every gem diamond is a 3-Dimensional and dynamic work of art. No one can capture diamond beauty in a single photo. Any photo is a mere snapshot of the full-motion picture of potential diamond beauty.

Perfection has always been a moving target. To be sure, lots of research has been done during the 300+ year development of the modern round brilliant. Cutters have always striven to do their best. Gemologists and other scientists have resolved to understand the complex math and physics.

And, of course, consumers have always voted for their preferences with their pocketbooks.

Suffice it to say there is no international standard defining appropriate light return. But yes, in a well cut diamond the majority of high intensity light that enters the diamond should return back to the viewer.

A diamond designed to return even 100% of low level light wouldn't be very desirable.

In general, the major trade labs have recognized that “light return” is a misnomer and the use of it alone is misleading in analyzing the overall “light performance” of high quality diamonds.

It has been shown that a small amount of "leakage" is not only unavoidable: it actually creates positive contrast effects that are quite visually pleasing.