An understanding of the colour, or temperature, of light is essential if you want to get the most from every subject and all situations. Not least because when you understand what’s going on you can take steps to avoid simple mistakes. It will also open up the most wonderful opportunities for capturing and emphasising colours in situations when you might otherwise be tempted to put away your camera.
In the days of film, we often had to put a ‘warm-up’ filter over our lens. These 81 series filters were tinted slightly amber in colour and took away the blue cast in a picture taken on an overcast, cloudy day. That’s because our Daylight colour film was formulated to produce correct colours – whites as pure white etc – on a sunny day with a few puffy clouds in the sky. Now, with digital, there’s not need for filters, all we need do is adjust our White Balance (WB) setting. It’s great, we even have the luxury of Auto White Balance (AWB). This acts like a sliding scale, correcting a little too much blue or a too much yellow in the light either side of ‘daylight’. AWB is not the answer to everything, but it’s good.
The colour (temperature) of light is measured on the Kelvin Scale, and our Daylight colour film was formulated to produce correct colours at around 5,500K (Kelvin). The same principle applies to our digital cameras. When the sky clouds over the temperature of the light actually goes up the Kelvin Scale. Maybe to around 7,000K. In deep shade on a sunny day the light can be very blue indeed – very high colour temperature. Perhaps about 8-9,000K.
Don’t panic! You don’t need to remember these numbers, but they do give you an idea of what’s going on. When you know what’s happening, you can use these different colours of light to create the most beautiful effects – and you can often change things by taking control of your WB settings on the camera. Understanding colour temperature opens up the most wonderful opportunities to manipulate things in the camera when you actually take the picture.
You’ll notice that what we naturally think of as ‘cold’, blue light is, in photographic terms, actually high temperature light on the Kelvin Scale. What people normally think of as ‘warm’ golden light (the yellow light from tungsten light bulbs, candles etc.), is in fact low temperature light. A tungsten light bulb is around 2,500K.
Unless you adjust your WB setting to Tungsten – that’s usually indicated by the little icon of a light bulb, or take a Custom WB setting, pictures taken in the light of ordinary light bulbs will have a yellow colour cast.
These massive differences in colour temperature can be used to great effect, particularly at twilight after the sun has set. There will not be a lot of light in these condition – it’s going dark – but what there is will be very blue (high temperature) indeed. As it is going dark, people will be switching on the lights in their houses (those light bulbs giving yellow light). This is a great opportunity to ‘mix’ these different light colour. You can produce pictures with deep blue outlines of the buildings with strong yellow light coming though windows. It’s called Mixed Light and can be highly effective. Advertising photographers use this trick all the time to make a subject such as a hotel look warm and inviting from the outside.
The rich golden light on this wall is actually caused by the midnight sun in Iceland. This is very low temperature yellow light. To maximise this colour, try setting your WB to the ‘cloudy’ icon. This will emphasise the golden effect even more
The low temperature yellow glow of the gas lights – yes this gentleman still had gas lights – has not been entirely corrected with WB set on AWB. This has injected extra atmosphere to the picture – and notice how blue the light is outside the window
Different colour temperatures are very noticeable here. The wall on which the melon sits is actually the same colour (from the same pot of paint) as that on the house in the background. The foreground wall is lit by soft, direct sunlight and has a natural white colour. The house in the background is in shadow and lit only by indirect reflected light from a blue sky – that is very blue high temperature light