Colour Rendering for Museum-Quality Art

Understanding colour rendering in the context of the magical paintings by Joaquín Sorolla, 19th century Spanish ‘painter of light’

Manoj Phatak, Founder & CEO of ArtRatio

Manoj Phatak, Founder & CEO of ArtRatio

Joaquín Sorolla – The Painter of Light

The Spanish painter Joaquín Sorolla y Bastida, born in Valencia in February 1863, was a master of capturing the poetry of sunlight on white sails, white dresses, white walls and above all, on water.

Mixing pure white pigment of yellow or vermillion with violet and blue, Sorolla produced the illusion in his works that sunlight truly sparkles, earning him the nickname ‘The Painter of Light’.

So to understand Sorolla is to understand the importance of rendering all the colours present in daylight.

But what exactly is colour rendering?

Well, ‘colour’ is simply the subjective appearance of a range of wavelengths of light as detected by the eye.

The term ‘to render’ means ‘to accurately reproduce’.

So, ‘Colour Rendering’ is the ability of a light source to reproduce all the colours present on an object, in comparison to a reference, which is daylight.

The ‘Colour Rendering Index’ (CRI), measured from 0 to 100, indicates how accurately these colours are portrayed.

Daylight, which has a CRI of 100, is defined as the maximum. Most LEDs nowadays have a CRI between 80 and 95.

Colour rendering applies both to ‘active’ sources of light (e.g. LEDs, tungsten filament bulbs) as well as ‘passive’ sources of light (e.g. windows, plastic films, filters, etc).

Colour Rendering Indices

The International Commission on Illumination (CIE), based in Austria, is responsible for the test procedures that determine the CRI of a light source.

The ‘General CRI’ indicates how 8 colour samples differ in appearance when individually subjected to the test light source, as compared to when the samples are subjected to daylight.

The “average” difference is recorded as a value “Ra”, but this 8-sample swatch does not include saturated red or blue. This has brought the ‘Ra’ definition some criticism from the lighting industry.

Some lighting manufacturers do now publish an “R9” score that includes a 9th sample, which is saturated red. By the way, the accurate rendering of saturated red is important for medical diagnoses. You can find out more at this link.

There is in fact an ‘Extended CRI’ (called ‘Re’) which includes 14 samples (including saturated red and blue) in its test swatch, and using this would lead to a more accurate assessment of colour rendering.

Unfortunately, not all lighting manufacturers publish this data, and not all customers know to ask for it.

Why is colour rendering important for the display of artworks?

If you place a red apple under green light, the green light will be entirely absorbed by the apple, and there will be no ‘red component’ to reflect back to your eyes.

The apple will now look black.

If you are not convinced, watch this video.

So you can imagine what happens when you use a light source that has only been tested by the General CRI, thus lacking tests of whether saturated reds or blues are accurately reproduced.

That’s right, the object will simply appear to lack some of the colours it contained when it was authored.

When you add to that an insufficient light intensity, the human eye will not receive enough light to allow for photopic vision either, further leaving colours and details hard to distinguish.

Smartglass for Artworks

You may be surprised to hear that the smart glass we use in our display vitrines has a CRI of 95, and the glass itself adds no further colouration, something you can see for yourself at this link.

If you want to know more about how smart glass can be used to display artworks with sufficient light quality and light quantity to allow photopic vision, whilst conserving the materials, check out our smart glass display products contained in the menu above.

References

  • The Sorolla Museum, “The Art of Light” URL
  • 3 Important Tips for Properly Lighting Your Artwork, URL
  • How to Light Your Art, URL
  • Illuminating Art: Choosing the Right Lighting, URL
  • Top tips to light up your fine art collection, URL
  • Let it Shine—Expert Tips for Lighting Art in Your Home, URL

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