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Optical Cut Analysis - Lightscope

Some content on this page are contributed by Good Old Gold, with thanks.

We desire well cut diamonds because of their desirable light return. So, wouldn't the best way to judge the cut quality be to observe it reacts to light?

Unfortunately, the lighting in most jewellery stores are unnaturally bright spotlights. Some people cover the diamonds with their hands or look at them under at table, but that does not work because we are trying to determine the diamond's reaction to various light sources. So, we cannot judge its beauty in the absence of light.

In addition, as a layman, it is very difficult to judge the cut quality just by looking at the diamond alone. That is where a LightScope would come in useful because light return and light leakage are quite obvious under the lightscope, even to a layman.

What is a Lightscope?

A LightScope is a simple device for viewing the light return of a diamond.

ImagescopeDifferent makers of LightScopes call their devices by different names. IdealScopes, FiresSopes and ImageScopes are all essentially the same thing. Of course, some are made better than others, but they perform the same function.

For the purpose of photography, the quality of the lightscope is very important since it has to work well with the digital camera and macro lenses, etc. However, for laymen, a simple IdealScope will suffice.

How does it work?

LightScopeThe facets of a diamond function either as a reflective mirror, or a leaky window. Therefore, we have to differentiate the two.

If we are able to tell if the origin of light is from the top or the bottom of the diamond, we will then be able to know if the facets are working as mirrors or windows.

To do that, we place a red cup with a viewing hole over the diamond. Then we place a white light source at the bottom of the diamond.

Whites: So, when we view the diamond, and see white, it means that the light is from the bottom of the diamond. This indicates that the particular facet showing white is not reflecting much light from the top. It is an indication of blatant leakage.

Blacks: If we see black or dark grey, this means that the source of light is directly from the top. Since we have a viewing hole on the red cup. Light coming directly from this hole appears black because it is the reflection from your eye.

Reds: If we see red, or dark pink, this means that the light is coming from the top, but at an angle. Light that has reflected off the surface of the red cup and onto the diamond will look red. Facets showing red or dark pink are reflecting a lot of light.

The lightscope depends on the reflection off the red cup to work. That is why the technology is sometimes called 'reflector technology'.

What do we wish to see?

If you have read the earlier section on Brightness and Contrast, you would have learned that a diamond's contrast is created by having a good combination of light coming from different angles. Since the lightscope shows light coming directly from the top as black, at an angle as red and from the bottom as white, we can evaluate the diamond quite easily.

Star and Hotspots

We want to see a good combination of dark reds and blacks. This means that the the diamond is reflecting a lot of light from light sources facing the diamond, and is therefore more brilliant.

Typically, a more brilliant diamond will also have more fire.

Having a good balance of blacks and reds contribute to scintillation because the light reflected would keep changing angles as we move the diamond. Remember, blacks are light reflected directly from the top, while reds are reflected at an angle. That is why Hearts and Arrows diamonds are amongst the most beautiful since the black arrows are usually very distinct and evenly spaced out.

Having more black 'hotspots' (I have pointed some hotspots out with yellow arrows) also contribute to scintillation.

You will learn more about what causes these stars and hotspots, and how you can pick out a diamond with the pattern you prefer later, in the section on Key Minor Facets.

Leakage Contrast

Since leakage can improve contrast, we want to evaluate this as well. We want to see a good representation of whites at the edge of the diamond in the distinct edge leakage pattern as pointed out by the green arrows. This will vary the light return at the edge of the diamond to improve the contrast brilliance and hence the beauty of the diamond.

However, we must be careful not to contrast edge leakage that provides contrast, to blatant leakage caused by girdle digging. Too much leakage will only lower the brightness of the diamond.

If you do not see enough edge leakage, then the diamond is said to have 'edge-to-edge brightness'. This is caused by girdle painting. Whether you like edge-to-edge brightness is a matter of taste.

We will discuss both girdle painting and digging in greater detail later.


Since January 2006, AGS has been using reflector technology to evaluate the cut grades of their diamonds. It is called the Angular Spectrum Evaluation Tool (or ASET for short). This is not surprising, because we can derive a wealth of information from these tools. One of the key objectives of evaluating a diamond's proportions is to assess its light return. As such, reflector technology makes sense since it does exactly that.

We will evaluate the AGS ASET in greater detail later when we discuss how they determine their cut grades, but you can skip ahead if you cannot wait.

Lightscope Photography

Internet vendors rely heavily on lightscope images to sell their diamonds because the customer cannot view the diamonds for themselves before buying. But be warned, that not all lightscope images are alike. The position of the red cup on top, as well the intensity of the white light from the bottom have a great impact on how the final image looks. For example, if the light source is too strong, the image will appear washed out and unclear. If the light source is too weak, you will not be able to tell the pink areas from the dark reds.

To illustrate this poitn, we present 2 lightscope images of the same diamond taken under different equipment setups:



Next, Let us take a look at a few more Lightscope images to learn what we can tell from looking at them.


Next: Gallery of Lightscope Images...