Accurate colour is important to all photographic artists and critical in achieving the perfect print. From exposing or capturing the image through to printing and installation, minor adjustments of colour can create different emotional and psychological responses. With this in mind – how important is colour temperature in viewing a work of art, and should artists consider this when approving colour tests?
Let’s talk about Kelvin…
Degrees Kelvin (K) is a value for expressing the colour of light. The relationship of colour temperature to colour perception is not obvious due to the remarkable ability of human vision to compensate for wide variations in the spectral distribution of light sources. Tungsten (or incandescent) light gives off a warm, yellow-orange hue (2700K-3300K). Fluorescent cool white light gives off a cyan-green hue (3500K-4000K), daylight fluorescent is the closest to ‘white’ daylight (5000K) with a blue hue and warm white fluorescent has a magenta-orange hue (2700K-3000K). Depending on the time of day, daylight may appear to be different colours. Daylight is 5500K-6500K. Since ‘white’ light covers a broad range of color temperatures, how is our perception of a work of art affected by the choice of illumination? Is there an ideal white light, i.e. is there a preferred colour temperature for viewing works of art and should the artist take this into consideration when printing?
Considering you do not always have control over the type of lighting your photographs will be viewed in, it is difficult to know what colour temperature to print to. A gallery may have tungsten, fluorescent, or a mixture with daylight. You may also want to exhibit the work more than once under different lighting conditions. The general trend in the past has been to print your work to daylight (5000K) as it is ideal in terms of excellent colour rendering. However, museums and collectors will generally exhibit work under tungsten as it is the least damaging to photographs whilst rendering accurate colour, and it is more commonly found in the home.
The ability of light sources to render colour accurately is crucial in museums. The standard measure for this is the colour-rendering index (CRI). Conventionally a CRI of 100 represents daylight. The best source of light in this respect is Tungsten Halogen with a CRI of 99. We are already aware that tungsten halogen is quite different than daylight, so far as it is much stronger in the red-yellow end of the spectrum. However, it does share with daylight a continuous spectrum, which is a key factor in human response to light. The only other light sources in the range of CRI 90-100 are some fluorescent lamps. These do not have continuous spectra (Lux and Kelvin are not continuous). However, they do get reasonably close to the response of the eye. At present Tungsten Halogen is the first choice for lighting museums, with high colour rendering fluorescent second.
Let’s talk about Lux…
Lux is a measurement of the light intensity falling on a surface. A problem with natural light is that all visible light is not equal. The amount of fading of an artwork caused by a 50 lux of UV filtered daylight is not equal to the amount of damage cause by a 50 lux of filtered UV fluorescent light, and neither is equal to damage caused by 50 lux of UV filtered incandescent light. The more violet and blue the source contains the more damage occurs, since these are the highest energy visible light wavelengths. The higher the colour temperature, the more violet and blue is present. Incandescent has the least. Fluorescent has more then incandescent, but it depends on the colour temperature of the lamp. Daylight has the most, and will cause the most damage even if lux levels are equal.
It is interesting to also note that due to the interaction of the rods and cones in the human eye, the colour of different light temperatures will appear different depending on their intensity. Basically the higher the Kelvin value, the higher the lux needs to be, to appear white to the human eye. It is the amount of light which triggers a larger visual influence of the cones for higher illumination and rods (blue sensitivity) for lower illumination. ie. Daylight and fluorescent needs to have a greater lux then tungsten to appear white.
This reinforces that tungsten is the best choice of light to exhibit and view work under as it has accurate colour rendition, consistent output and the lowest amount of damaging UV rays in the lowest output.
* 150 lux (or less) is considered o be appropriate for viewing (exhibiting) photographs
* Incandescent (tungsten) is the most archival lighting to view artwork.
The Colour Factory has checked the colour temperature and lux of its lighting, and have the option for you to view your tests and prints under (UV filtered) white daylight fluorescent 5000K, 220 lux and will shortly be offering museum standard tungsten halogen at 2700K, 150 lux.