Light and Light

Have you ever noticed an artwork change appearance under different lighting, perhaps a print, a painting or even yourself?   There’s light, and then there’s light., and poor lighting can fall short of a pleasing rendition.  Here’s a little explanation that might help demonstrate why, along with some measurements I took the the other day.  I love it when art and science come together, it’s the engineer in me.

Have you ever thought of music in terms of layers?  Perhaps the violins are rising on one layer while the brass deepens on the other.  In a way, music can be perceived as separate layers of sound made up of individual frequencies.  Light also consists of frequencies, but we perceive colour very differently to sound.  The colours we see are actually a simplified mix of all these frequencies, our eyes and brains simplify this rich mixture of individual frequencies into a single colours, each with a unique hue, lightness and intensity.  If we mix two colours together, we end up with a new colour, we don’t see two colours at the same time.  If we mix two sounds, we hear them together.

The colours perceived in an artwork depend on the way it’s illuminated.  Most of us probably know that white light is made up of all colours, well that’s mostly true, but it’s also possible for light to appear white when it’s missing some colours.  To bring out everything in an artwork, a good light source needs to include a wide range of  colour across the visible spectrum, ideally that spread will be similar to natural daylight.  The acoustic equivalent would be something like the ‘white noise’ which can be heard in between radio stations.  White noise is simply a jumbled mixture of frequencies happening at the same time.

The diagrams below show how different light sources are comprised of different colour mixes, the measurements were taken from various light sources around my home.  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 this particular LED looked quite blue.  Artwork viewed under ‘peaky’ light can become flat and lifeless.

light spectrum from 6 different sources

Daylight is often used as a reference in specifications, here I’ve measured the midday sun outside my studio which is similar to the a standardised light source called D50, as you may expect.

The Normlight fluorescent tube is a well corrected print viewing light which simulates daylight, like all fluorescent tubes its colour comes from glowing phosphors which make it a little ‘spikey’ but it’s still much better than a cheap household fluorescent tube.

The Bowens strobe (studio flash) is surprisingly close to daylight, and the household LED from my dining room is pretty typical for household lighting.

Lights are normally labelled with a colour temperature (CCT) representing how cool or warm they appear, but just as important when it comes to viewing artwork is the CRI value, which represents the quality of the light.  Light sources with a high CRI will render the colours of real life objects best, because they themselves, are made from a smooth mix of colour.  CRI numbers above 90 are pretty good, or for colour critical applications even higher values are better, such as 95 or 98.

So by measuring the CRI of the light sources around my home, I can get an idea of  they way they render artwork.  None of the artificial lights are as good as pure daylight, apart from the strobe.  The cheap LED was particularly bad, and it’s poor colour rendition is obvious, the household LED and fluorescent lights aren’t perfect, but are reasonable for every day viewing.  The Normlights or high CRI equivalents are useful when making prints in colour calibrated workflows, or for artists wanting to paint after dark when the daylight has gone, since regular household lighting or cheap fluorescent tubes can shift the colours a little.

  • 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.

John Hardiman