Gems & Lighting

The colour impression made by a gemstone is dependent on a remarkable number of influencing factors. There is the nature of the light source, the colours of the surroundings and background, and then of course the ethnic disposition of the man or woman who wears the stone. In addition to that, the eye of the beholder with its own individual colour perception and age, as well as its own particular traditional aesthetic sensibilities plays a part, too.

By Manfred Eickhorst, article first published at the ICA website www.gemstone.org.

So it is that this colour impression made on the gemstone lover will vary again and again at different times of the day and in different seasons, and this too lends a certain charm in our perception of it.

Comparison with Nature’s other coloured “gems” helps us to understand these interactions; for example the flowers in our garden, whose colour in the morning may appear to us quite different to their colour in the afternoon or evening. They are a delight to our eyes with the variety of their colour in the natural daylight, but also when used as decoration in artificial light.

In the flower shop, when they are arranged and presented to us, we are often astounded by the dramatic beauty of their colours, as we would be by an actor spotlighted on stage. No one would consider lighting that stage as you would an office. What makes an impression on the observer is good, accentuated light that brings out the best in its subject.

This applies to the world of gemstones in a similar way. We don’t really come to appreciate their beauty until they are captured, like those actors on stage, in a beam of carefully set light, such as LEDs, quartz halogens or full spectrum fluorescents. This in fact is the secret of the fascination held for diamonds. It’s extremely high refraction means that it lights up even when there is only very little incident light, though it must be said that the perception of its body colour is more difficult, and affected by its cut and especially its size.

Coloured stones, on the other hand, have lower refraction, but as they are typically larger than diamonds, their colour presence leads to a more intense impression. Having said that, the cut, i.e. the surfaces by which the incident light is reflected and refracted, is of decisive importance. It opens our eyes to the colour universe of the gemstones. The cut is a window to the variety of those colours, which run across the whole spectrum of the rainbow; colours which, in their origin, lay hidden within the rough unpolished stone.

The impression made by a coloured gemstone and its sensation to the observer is influenced by a number of unique color attributes: hue, lightness (tone/value) and saturation of the colour (chroma/intensity), as well as dichroism and dispersion. 

Together with the influencing factors already referred to, these determine how we actually perceive the gems and their colours. On account of these many variables, gemstones have the ability to surprise us in different guises again and again.

Professionals who work in the world of gemstones, such as the members of the ICA, are by no means immune to this variability either. It is they who accompany the gem material on their long journey, from the moment they leave the mine, and get polished; up to the moment they become parts of jewellery. It is their highly unique abilities which ensure that the true value of gemstones is brought out and, when all is said and done, that the wearer can derive pure enjoyment from them. In view of the diversity already described and the rarity of the stones, this is thoroughly challenging work. Experience and integrity, and a background which in many cases goes back over several generations, mean that the world of coloured gems is quite different to that of diamonds or pearls. 

Thus the right kind of light and the optimum cut supports each stone in its natural beauty, to the delight of the person who wears it and the ones who are admiring it.

About the author:
Manfred Eickhorst received his MSc from the Technical College of Applied Physics Hamburg. He has developed, designed and engineered specific lighting and instruments for gems, jewellery, and gemmology. His expertise regarding light and optics is demanded worldwide. The articles he publishes are well known contributions as professional references for the gemmological community.

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DIALITE Classic - Daylight lamp for diamond grading with optional UV light

DIALITE X - Pendant lights