Colour enhancing or colour intensification based on TM30

Having explained elsewhere how SORAA has developed the Vivid range of light sources with very high colour fidelity, I would now like to explain another class of so-called "colour-enhancing" or colour-enhancing light sources in more detail. Today I will give some general explanations of this concept, and in a follow-up post I will look at how exactly the SORAA products provide this enhanced experience.

Firstly, let's take another look at an image I've already shown elsewhere here on the danholt Licht BLOG:
An illustration of the Rf-Rg diagram.

As we now know, Rf describes the colour fidelity - in other words, whether the colours match the natural colours. Rg, on the other hand, describes whether the colours are on average too little saturated (low gamut) or too much saturated (high gamut). And of course there is a trade-off between Rf and Rg: if we choose a light source that oversaturates a certain colour (and thus increases Rg), the corresponding colour distortion also leads to a reduction in Rf.

As this may all sound a little theoretical, let's illustrate it:

In the figure above, we compare three light sources. The middle light source has a very high Rf value (>90) and therefore causes only slight colour distortions: Accordingly, the TM-30 colour field shows very short arrows. As a reminder - these arrows show how and where colours are distorted.

The source on the right makes green and red colours more saturated - as can be seen both in the image and on the TM-30 colour patch, whose arrows point outwards towards more saturation - their gamut index Rg increases, but their fidelity index Rf decreases due to the colour distortion. The source on the left, on the other hand, desaturates greens and reds and has low values for Rf and Rg.

Now look at the images and ask yourself which one do you prefer? If you put this type of question side by side in a scientific study, many participants would rank the source on the left lowest and the source on the right highest. In other words, the "preferred" source is not the one with the highest Rf value, but the one with the highest Rg value. Hence the use of the word enhancing for sources with an Rg value above 100.

When should we use such colour enhancing light sources? This is an interesting question to which there is no simple answer.
First of all, we need to realise that just because something is preferred in a comparison experiment does not always make it better. Let me give an analogy here: If you serve two otherwise identical dishes, one of which contains more salt than the other, most people will favour the saltier dish. However, we certainly don't conclude from this that more salt in our food is always better!

On the contrary, we like to season our dishes carefully - and the same applies to colours. In some cases, colour fidelity is most desirable - for example, when we want to sell a product and present it as it appears under natural sunlight. Think of food, clothing or make-up, for example...
In other cases, colour enhancement may be appropriate - think, for example, of a restaurant where the colours of the food should appear deep and rich, or a lounge bar with warm light that makes people's skin appear more tanned... In short, the answer depends very much on the application - and also on the artistic taste of the lighting user.

I should mention at this point that the concept of colour enhancement and colour gamut metrics is not new and predates the work on the TM-30 by decades. However, as we will see, the exact derivation from TM-30 is particularly instructive for practical applications.

Now that we understand the basics of colour enhancement, the next question arises:
How can we design a good colour-enhancing or enhancing source in practice? We will deal with this in another article...

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