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Light and Light

There’s light, and then there’s light.

When it comes to viewing prints, artwork or even each other, our lighting can fall well short of a pleasing rendition.  Here are some measurements I took the the other day which can help demonstrate why.  I love it when art and science come together, it’s the engineer in me.

Music can be perceived as separate layers of sound made up of individual tones, the tones are really the individual frequencies heard together.  Light also consists of frequencies, but we perceive colour differently to sound.  The ‘tonality’ of light is all around us but can’t be seen, that is, we can’t see the individual frequencies making up light like we hear individual sounds.  Our eyes and brains simplify this mixture into colour, each with its unique hue, lightness and intensity.  Unlike sound, if we mix two colours together, we get a new colour, rather seeing two colours at the same time.

The colours perceived in an artwork depend the way it’s illuminated.  A good light source consists of an even spread of frequencies, the acoustic equivalent would be something like ‘white noise’ which you can hear in between radio stations.  White noise is just a mixure of random frequencies without bias.

Have a look at ‘mid day sun’ below, that’s about as good as a light source gets.  It’s not biased towards particular frequencies in the spectrum (or tonalities if you’re thinking in terms of sound).  Now have a look at the spectrum of the cheap LED, the two distinct peaks show it’s bias and as a consequence it looked quite blue.  Artwork viewed under it became flat and lifeless as the colours merged together.

These measurements were taken around my home and studio.  Mid day sun is the basis for many standards, here I’ve measured the sun at 2pM outside my studio which is similar to ‘standardised’ daylight (eg D50).  The Normlight fluorescent tube is a well corrected print viewing light simulating daylight, like all fluorescent tubes its colour comes from glowing phosphors which makes it a little ‘spikey’ but it’s actually quite good when you compare to the regular fluorescent tube from my pantry.  The Bowens strobe is a camera flash tube and it’s surprisingly close to daylight.  Then there’s the household LED from my dining room which is pretty typical for household lighting.

Lights are typically designated with a colour temperature (CCT) representing whether they appear cooler (bluer) or warmer (yellower), but just as important when it comes to viewing artwork is the CRI, the evenness of the light spectrum.  The higher the CRI, the more even the light spectrum, and typically the better it will be for viewing artwork.  CRI numbers above 90 are pretty good, or for colour critical applications above about 95 or 98.

The CRI for the light sources above were:

  • Mid day sun: 99
  • Normlight: 94
  • Regular household fluorescent (from my pantry): 85
  • Bowens strobe: 99
  • Household LED (from my dining room): 83
  • Cheap LED: 69

So hopefully this little science lesson can help you see the invisible, and better understand why lights aren’t all equal.