Light only becomes coloured when part of the spectrum is missing. As can be seen from the Outdoors at Night exercise, the colour of man-made light can vary too. In a similar way to the atmosphere blocking shorter wavelengths at sunset, causing an red/orange light, different artificial light sources can emit only a limited range of the spectrum and appear coloured.
An obvious demonstration of this is when we walk into a building lit with LED lamps from the outdoors on a bright day. Direct sunlight contains a full spectrum and so is ‘white’ or colourless. Lighting that emits only colours from the shorter-wavelength end of the spectrum will give a cooler, clinical feel.
Another example of colour differences is when driving a car at night with traditional filament headlights as our eyes adapt to the colour of the lights of the car we are driving and we see this colour as white. Other cars with the same lights also appear white. More modern halogen lamps appear will blue. Now switch to a car with HID lights and traditional lights will look yellow for the same reasons.
Our cameras will attempt to correct this either automatically (AWB – Auto White Balance) or by using a pre-set corrections (tungsten, fluorescent etc.) similar to those used to correct outdoor lighting conditions (daylight, cloud, shade etc.).
To demonstrate this, I shot the following pictures of a room lit firstly with a tungsten filament lamp and them with an LED spotlight. According to the IKEA website, the LED has a colour temperature of 2700K, meaning that it is a warm light (for an LED) and close to that of a traditional filament lamp (we are familiar with this lighting in a residential setting; it feels warm and homely). This chart shows where these lamps sit in the full colour spectrum.
Through the curtain, evening daylight is visible. It was a cloudy evening and so the light was evenly diffused and fairly flat. Because natural lighting is so much brighter than artificial light,I had to wait as late as possible (before the street lights came on) to balance the light level with that of the interior. All exposures were more than 1.5s.
Tungsten light source
Warm-white LED light source
As in the previous exercises, these pictures demonstrate that the white balance settings can correct for different light sources and will produce acceptable results even when the light sources are mixed as they are here. The photographer can use the various setting to reproduce the part of the scene that they need a faithful reproduction of. Or, as in this example, they can use the setting creatively to give a feeling of warmth.