What makes a diamond a diamond is light. Light is everything. It’s the source of a diamond’s beauty. Without light, there are no reflections. No sparkle. No brilliance.

Office Lighting & Day Light

When light leaves the sun, it zooms towards the earth at 186,000 miles per second. When it hits the diamond in front of you, it slows down to 77,000 miles per second. That speed difference is something you can see. Light in diamonds bends, reflects, refracts, and breaks apart into rainbows of color. Light is what gives us diamond’s brilliance, scintillation, and dispersion.

Of course, when I’m talking about light in diamonds, I’m talking about the cut. Each facet that a cutter polishes onto a diamond is designed to reflect light, bounce it around the diamond, and up to your eyes.

Even one facet out of alignment can result in light that doesn’t perform the way it should. That’s why simply calculating a diamond’s proportions and angles isn’t enough. There are a wide variety of proportions that result in a beautiful diamond. But no set of numbers guarantees beauty.

And all light isn’t the same. Because light is so essential to understanding the optics and the beauty of diamonds, the type of light matters.

This is the most overlooked part of understanding the quality of diamonds. But you have the perfect instrument to analyze the impact of light on diamond quality: your eyes.

Look and Look Again

Diamond facets are like mirrors: they reflect what’s around them. When you look at a diamond from far away, it reflects the room and environment around you. When you look at a diamond close up, you’re seeing a reflection of yourself. You’ll be able to see the color you are wearing reflected in the diamond’s facets.

Differences in light are even more important. In direct sunlight, all diamonds look great. They flash and sparkle and throw off rainbows. You can’t judge whether or not a diamond is well cut by looking at it in direct sunlight.

Jewelry stores have spotlights that are just as flattering as direct sunlight. You’ll fall in love with diamonds easily in this light. They will all be brilliant and sparkling. Shining a spotlight on a diamond brings out its fire, just like sunlight does.

The light in an office is efficient but generally not flattering for diamonds (or for people!). Usually, it’s diffused light that bounces off the ceiling. With diffuse or scattered lighting, a diamond’s brilliance is more visible. Light enters the diamond from multiple directions, downplaying shadows and decreasing fire.

Candlelight and warm home lighting are good for people and for diamonds. You won’t see optimum brilliance but you will get sparkle. Diamonds with larger facets like old European cuts and emerald cuts will look especially good in these lower lighting environments.

Daylight or indirect sunlight from a window, especially a north window which provides more consistent illumination all day, is the most important light for looking at diamonds. I never buy a large diamond without looking at it in daylight.

In daylight, you’ll see what a diamond really looks like. It’s bright enough to assess its brilliance and scintillation without those blingy reflections that blind you to the areas where light is leaking and not being reflected back to the eye.

A diamond that’s beautiful in daylight will also be beautiful in every other light. That’s why diamond dealers sort diamonds only in north light.

You can have two diamonds with identical GIA reports. They look the same in-office light or jewelry store light. Put those two diamonds on your hand and take them to the window and look at them in daylight. Look close up. Look from farther away. Rock them back and forth and let the light play on the facets. You’ll discover that they aren’t the same at all. The light will reveal much more than any report can.

This is especially true of fancy shape diamonds. You can’t tell what they look like at all just from the report. No two are alike. I’ve trained my eyes for years and they still surprise me.

Which diamond looks most beautiful to you is personal: you may prefer one facet pattern to another. Diamonds have different rhythms to their scintillation and different personalities. I gravitate to step cuts and you might like the crushed ice look of a radiant cut. There’s no wrong answer, it’s just a personal choice.

If you are buying a diamond for yourself, pay attention to your personal preference for the pattern of light reflecting inside the diamonds you’re considering. Think about the lighting conditions you’ll wear the diamond in and make sure you view the diamond under those conditions. For example, if you work in an office under fluorescent lighting, ask to see diamonds under fluorescent lights until you find that one diamond whose sparkle and brilliance speaks to you.

Big Differences in Small Diamonds

Because they generally don’t have grading reports or cut grades, most jewelers don’t think about how the small diamonds they set in their jewelry handle light, especially diamonds under

10 points. For many years, people marketed that their jewelry was set with full cut round brilliant melee instead of single cut diamond melee, which has only 16 facets.


To me, that’s crazy because I’ve seen many single-cut diamonds that are beautiful and the world is full of small diamonds that are not cut well at all. I always advise my clients never to sacrifice on cut of their melee diamonds. It makes a huge difference in the beauty of a diamond piece and it doesn’t add much cost.


Your eyes will easily detect the difference: the well-cut melee will be brighter, more brilliant, and will actually look larger, even compared to less well-cut melee with higher color and clarity.


When that piece of jewelry with well-cut diamonds is worn in daylight, in-office light, in candlelight, in sunlight, and even in moonlight, it will be more beautiful, with its diamonds dancing in the light.


Understanding diamonds and light will make you a better diamond buyer. At K. Rosengart, we’re proud to offer you large and small diamonds with excellent light performance. We look at all our diamonds to ensure they are ready for the spotlight.