Everything the Artist Needs to Know About Lighting in the Studio - Colour Spectrum (Part 2 of 5)

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Colour temperature is important in determining how a work will appear at different times of day, or in different lights.  However accurate colour reproduction under artificial light is equally affected by the colour spectrum of the light produced.

 The colour spectrum of a light source has a significant effect on how accurately colours are reproduced.  Look at a rainbow, created by the sun, and you will see the colours spread uniformly from red to violet.  However, if we split the light from some artificial light sources into their spectrum (e.g. through a prism), there may be gaps in the spectrum produced.  These gaps will have a significant bearing on colour reproduction – if there is a gap in the yellow region, then yellows will not be reproduced well  when viewing under that light, while colours which reflect yellow light (e.g. orange) will be out of balance with other colours.  The consequence is poor colour rendition, as different colours in your artwork will be out of balance with each other.

 This is a different problem to colour casts such as from low colour temperature light sources.  Here, most of the colours will be balanced in intensity when the art work is viewed, but colours towards the red-orange end of the spectrum may be enhanced in comparison to bright noon daylight.  This is entirely different to when a light source’s spectrum causes greens to appear as black, for instance, but reds, oranges, blues and violets reproduced faithfully.  Therein lies the difference between colour temperature and colour spectrum issues.

A good (extreme) example of gaps in the spectrum are the orange sodium vapour lamps often seen in street lighting – highly efficient, but with significant gaps in the visible light spectrum.

Some compact fluorescents can suffer from incomplete spectrum problems, as some focus more on achieving a particular brightness and colour temperature than colour reproduction.  There is no easy way to know which compact fluorescents (sometimes known as energy saver lamps) are better or worse, though some are marketed as “full spectrum” lamps.  In this case the phosphors (the white stuff coating the inside of the tube) are chosen on the basis of achieving a full and complete colour spectrum.  Fluorescent tubes (that’s the long tubes as opposed to the moden compact types with a bayonet or Edison screw fitting) do not always suffer this problem as they have long been used in applications requiring good colour reproduction, and have had significant time spent on improving phosphors - see the next article entitled ‘Types of lighting’.

 As well as gaps in the colour spectrum of a light source, there may also be uneven weighting of colours within the spectrum with certain lighting sources.  Photographers know that many older type fluorescents (using old (non-modern) phosphors), and mercury vapour lamps,  produce a strong green cast as well as having incomplete or un-natural spectrums . In contrast the old incandescent lamps produce a full spectrum but more light in the orange-yellow range than the blue violet (unless you buy a daylight corrected incandescent – see below).  Most modern low voltage halogen and xenon lamps also provide a full spectrum coverage, and are also good for accurate colour recondition.  The only problem with these non-fluorescent options is limited choice of colour temperature, which is problematic if you wish to simulate sunlight/daylight at mid-day. 

In summary colour spectrum affects the accuracy of colour reproduction (as we see things under the light source), and is an important consideration when choosing lighting.  However, colour temperature is equally important for determining how a piece of artwork will appear in daylight, or under actual lighting conditions after installation.  Very much you need to consider both colour temperature and spectrum if you intend to work or review artwork under artificial light.

Interesting Links

full spectrum energy savers- http://www.viva-lite.co.nz/

Daylight corrected incandescent bulbs - http://www.lampspecialists.co.nz/productPDFs/5041h.pdf

Fluorescent tube data http://www.lightaudit.com/data/phillipsfluorescent/master_tel5_high_efficiency.pdf