Life is a long quiet river…
“Life is a long quiet river” is the poetic title of a 1998 French comedy (La vie est un long fleuve tranquil). Somehow that seems to fit what I do – working with cameras and fishing for light. No dramas as such. The sun comes up and goes down every day, the light meanders, and I am a spectator watching the ebbs and flows.
For most photography, exposure and the colour of light are adjusted automatically by the cameras (and cell phones) of today which do an amazing job. But in our profession we need to understand a little of what is going on.
Take electric light for example. In the early days, the warm glow produced by a hot filament was quickly preferred to the blueish light of the gas lamps. But since then, bulbs have been created to satisfy all kinds of needs: to add ambience, to set the mood, to help plants grow, to control the light for precision colour matching. We work with light, we need to understand how colour temperature affects what we see.
Measuring the different colours of light
The colour of light is measured in degrees Kelvin, a thermometric scale invented by Lord Kelvin (1824-1907), ranging (for our purposes) from 1,000K to 12,000K or so. Simply put, it means the higher the K reading is, the whiter or bluer the image will be. Similarly the lower the degrees on the K scale, the yellower or redder the light will be.
For example, the standard, incandescent tungsten bulbs everyone uses in their homes (or used to) burn with a yellow/orange light from 2,700–3,300K. It corresponds to a soft welcoming colour, flattering like sunlight in the late afternoon. The red/orange of candlelight is warmer still at around 1,700K. And the colour of the flames in a wood fire might be as hot as 1500K or hotter.
In video production, we sometimes use Halogen lights although the bulbs get burning hot and use a lot of power, and the light they produce is a warmish 3,200K. However over the last few years fluorescent tubes have been used in video because they give off very little heat, use less power and provide a soft, even light. And they are now available at two different colour temperatures from a warm 3,200K to a coolish 5,500K (N.B. only those marked with a CRI (colour Rendition Index) close to 100). As for photographers’ strobes, studio flashes are rated at 5,500K, close to the 5,600K temperature of sunlight light at midday.
Coloured gels can be used to balance the light, but it seems as if LED (Light Emitting Diodes) lights really are the future. They are inexpensive, portable and use little power. and unlike old-fashioned bulbs, they don’t have a filament to burn out since they shine through the movement of electrons in a semiconductor. And LEDS can be temperature matched and some are even temperature variable.
However, if you have really deep pockets, and don’t care how hot lights get, how much power they use or how large they are, the best way to light a studio is still with mercury vapor HMI lights, high power medium arc-length lamps made specifically for the film and entertainment industries.
The bottom line, is that even if your camera will do much of the work for you, understanding the colour of light is fundamental to film-making and photography – and there is still a place for colour temperature meters and light meters to help judge exposure.