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Two diamonds look dark in sunlight, one looks great!

Why Do Some Diamonds Look Dark In Sunlight? This comes about because the better the Light Performance of a diamond the darker it will appear in direct sunlight. In next week’s blog we will discuss Strong Blue Fluorescence effects in diamonds and dispel some mistaken concepts.

Light performance

Essentially the better a diamonds Cut Quality, the darker it will appear in direct sunlight. Strange? Read on and discover why. One of the most common reasons why a diamond appears to be darker under direct sunlight is due to the diamond’s light performance which is related to the Cut Quality of the diamond.

There is this common misconception amongst consumers that a GIA (Gemological Institute of America) approved Triple Excellent Cut Quality Brilliant Round Cut diamond is good enough when the proportions, polish and symmetry all being excellent according to GIA should mean that the diamond is a high-light performing diamond. Consumers also tend to assume that investing in a high colour and clarity diamond would make the diamond appear whiter, brighter and more brilliant. However, the brightness of a diamond has little to do with the diamond’s colour or clarity grade.

Diamond Cut is king!

When talking about the brightness of a diamond, it’s best to measure a diamond’s light performance based on its cut. It is unfortunate that GIA does not grade the light performance of a diamond. Meaning that a diamond with an excellent cut grade can still be a very poor light performer. GIA only grades the proportions, polish and symmetry with a broad range qualifying as the best or ‘Triple Excellent’. Fully 76% of round brilliant cut diamonds are given the top grade by GIA. Less than 7% receive the bottom 3 of the 5 grades Good, Fair and Poor!

IMAGE I illustrates 5 different cut styles under direct sunlight. As you can see the Ideal Round Cut Diamond on the right appears to be the darkest amongst the 3 diamond rings.  The darker a diamond appears to be under direct sunlight, the better and brighter the cut will be.

diamonds look dark in sunlight

IMAGE II: Centre Stone-Left- Cushion Cut; Centre Stone-Middle- Marquise Cut; Centre Stone-Right- Ideal Round Cut Diamonds under Shade Lighting.

The best lighting to view the brightness or brilliance of a diamond is under a cloudy or diffuse light setting as seen in the image II above or Garry Holloway’s video of a 5.14 Carat D Colour VVS2 Clarity Brilliant Round Cut diamond. IMAGE II illustrates the same diamond rings as shown in IMAGE I under a Shaded lighting environment. As you can see the Ideal Round Cut diamond now looks to be the brightest.

Spot lighting in shopping centres

Under LED/ Direct Spot Lighting which is typically found in shopping centres is where you get to see the brilliance, fire and scintillation of the diamond. High-light performing diamonds such as the Brilliant Round Cut diamond used in Holloway’s video are cut to have large bold flashes where the arrows flare up very intensely. This is what makes the diamond eye-catching.

What do these terms mean?

Scintillation is how the light emerging from the diamond plays and flashes and gives the diamond its sparkle.

Fire of the stone is how the facets refract and disperse the light into the colours of the rainbow. As you move the diamond through the light, you see flashes of blues and reds within the diamond.


This is why we always emphasise so strongly on the cut and why is it so important to check the light performance of the diamond using an Ideal-Scope. The GIA certificate does not grade the light performance of the diamond or review its light leakages, therefore, using an Ideal-Scope would help you gauge the brilliance (the proportion of light which is reflected back to your eye) of the diamond.

There are a lot of poor light performing diamonds that are being sold to uninformed consumers every day. In fact, the majority of diamonds that are in retail stores and sold online are those that you wouldn’t buy once you’ve assessed it with an Ideal-scope. So if you’re planning to buy a diamond from your local jewellery store, it’s a good idea to invest in an Ideal-Scope. When shopping online you can ask for an Ideal-Scope photo.  What you’re looking for in a well-cut diamond are dark symmetrical arrows with the rest of the diamond being bright red or pink.

diamonds look dark in sunlightdiamonds look dark in sunlight
Yellow Cushion Cut Diamond Under Direct SunlightYellow Cushion Cut Diamond Under Shade Lighting

Table III: Fancy colour shaped diamond under Shade Lighting and Direct Sunlight.

Yellow Diamonds

Consider the fancy yellow coloured cushion cut diamond in Table III. It is the brightest under direct sunlight and the dullest in shaded daylight. This ‘crushed ice’ style of diamond cut does not show much brilliance at all but is exceptional at ‘trapping’ light inside a diamond, therefore, enhancing its colour. If this diamond had been cut into an ideal round cut it would be very pale yellow and less attractive.


Another reason why your diamond may not appear as bright as it should be is due to inclusions that can cause your diamond to have a dull milky appearance. Inclusion is a broad term used to describe flaws existing on the inside of a diamond.

If the entire diamond has thousands of microscopic inclusions it can cause your diamond to appear milky, this can happen on VS to SI Clarity grades. This is made worse if the diamond has fluorescence (see next week’s blog).  Retailers often classify these diamonds as ‘eye-clean’ as these inclusions aren’t visible to the naked eye. These inclusions are not even evident even when looked at using a 10x magnifying loupe. They usually require magnification of 100X or more to see the individual inclusions. In sunlight those inclusions stop the light travelling through and emerging from the diamond.


The two reason why some diamonds appear darker in sunlight is due to High Light Performance. The better the cut the darker a diamond will appear under direct sunlight. If you view the diamond outdoors then it is advised to shade the direct sunlight with your body. This is when you see the combined brilliance and fiery coloured sparkles most diamond lovers like to see. There are a lot of poor light performing diamonds that are being sold to uninformed consumers every day. So we advise you to purchase the Beginner Idealscope Kit when shopping for diamonds. Read next week’s blog to discover why the Ideal Cut Round Diamond appears blue. The cause is no the level of fluorescence of the diamond in strong Ultra Violet sunlight.