Gemstone Colors and Lighting

The perceived color of a gemstone depends in part on the light under which you view it. A ruby appears red, for example, because it aborbs all frequencies of light except for red. But all illumination does not have the same spectrum or color temperature, so a ruby will appear more or less red depending on the quality of lighting.

Color Temperature ScaleThis is a lesson that gem dealers know very well. When you are buying and selling valuable gemstones, mistakes in appraising color can be very expensive. Some dealers try to mitigate their risk by selling their stones only under optimum lighting conditions, while buying under less ideal lighting. While this 'buy under bad light, sell under good' might make sense for some, we prefer a consistent lighting environment that allow us to evaluate many different gems under the same balanced lighting.

Different qualities of illumination can be measured on a color temperature scale measured in degrees Kelvin. The scale indicates the hue of a particular type of light, with warmer colors such as orange-red at the lower end of the scale (1000K) and cooler colors such as blue-violet at the upper end (10000K).

Some lighting is rich in yellow and orange wavelengths, such as incandescent bulbs and sunlight at sunrise or sunset. Other light is rich in blue wavelengths, such as north skylight from a deep blue sky. Rubies will appear a more saturated red under warm light with a low color temperature, while blue sapphire will appear a more saturated blue under cool light with a high color temperature.

These differences can be quite dramatic, and even subtle differences are very noticeable to people who buy and sell gemstones for a living. In our office in Bangkok the natural light can be highly variable, with bright sunny days in the winter and overcast days in the summer. Light from the south windows of our office is quite different from the north light on the opposite side. 

Burma Ruby 2.61 cts Blue Sapphire Madagascar 2.42 cts
 Blue Sapphire

The most balanced light is white light or daylight in the middle of the day, with a color temperature of around 5000K to 5500K. This light is fairly neutral insofar as it is not particularily flattering to either red or blue gemstones. We mainly use lamps with daylight flurorescent bulbs with a temperature rating of 5000K. This give us a consistent and neutral lighting environment for evaluating gems. We use the same lighting for taking all the gemstone photos you see on our website.

See our selection of Fine Natural Gemstones