The colour of light

Now that you are up to speed with the quantity of light you need in a photograph it is time to get to grips with the colour of light. In this lesson, we learn about the colour of light and how it interacts with your camera's white balance. But let's be clear, we're not aiming for textbook accuracy; we're chasing beauty. The hues and tones in your photographs are your canvas and with a newfound understanding, you'll be well on your way to mastering your art. While terms like 'colour temperature' will make guest appearances, there's no need to memorise any numbers. Your eyes will be your guide, as you learn to intuitively set the mood and ambience in your shots.

That dress

Do you remember the dress that broke the internet back in 2015? It is a good example of how our perception of colour can vary from that of a camera sensor. It took over two years for scientists to establish why some people saw the dress as blue and black, while others as gold and white. People’s perception of colour is also informed by their perception of the lighting in the scene. The image of the dress, taken on a cellphone, contained a lot of uncertainty in terms of lighting conditions.

Colour temperature

Understanding the colour temperature of different light sources is desirable but not essential. However, with modern cameras, it's hard to avoid the Kelvin scale and it's what we use when setting white balance manually.

Our eyes can automatically white balance because our brain calls upon the lighting clues around us to help us determine the colour of objects. Cameras have no such AI so we need to tell our cameras exactly how we want our colours to look. Take a look at this video demonstrating the use of the Kelvin white balance control.

The Kelvin scale

Don't get too hung up on the numbers. It's worth using your eyes to set the colour mood rather than relying on the numbers. I've included the list below for completeness.

Here's a list of common light sources and their typical colour temperatures measured in Kelvin:

1. Candle Flame: Around 1,800K - It gives off a warm, orange glow, ideal for creating a cosy and intimate atmosphere.
2. Tungsten Bulbs (Incandescent): Approximately 2,700K to 3,200K - These bulbs emit a warm, yellowish light plus a lot of heat. They used to be used in household lamps.
3. Halogen Lights: Roughly 3,000K to 4,000K - These offer a more neutral, white light, a bit crisper than regular tungsten bulbs and are used in retail displays and low voltage downlighters but are being phased out to be replaced with far more efficient "warm white" LEDs.
4. Sunrise/Sunset: Typically around 3,000K to 4,500K - This light is warmer and softer, with orange and pink hues.
5. Fluorescent Lights: Generally 4,000K to 5,000K - They provide a cooler, bluish light, often used in offices and commercial spaces. There is usually a green spike in their spectral output that is not noticeable by the eye but can look awful on camera.
6. Daylight (Overcast): Around 6,000K to 6,500K - Offers a balanced, neutral daylight appearance.
7. Direct Sunlight at Noon: Approximately 5,500K to 6,500K - This is considered the standard for “white” light in photography.
8. Electronic Flash: Typically around 5,500K to 6,500K - Similar to daylight, providing a balanced white light.
9. Clear Blue Sky: Can range from 10,000K to 15,000K - Offers a very cool, bluish light.

The colour temperature curve

All the points on the black line in the diagram below are seen as white. A white piece of paper looks like a white piece of paper under orange light and blue light and at all of the points in between that appear exactly on the curve. If your light source produces light just above the line then it will exhibit a green tint and if below the line it will have a magenta tint. That is why colour editing programs use both white balance and tint sliders to represent the colour of the illuminant.

Tint

Some continuous lights have a tint adjustment as well as a colour temperature control. This tint adjustment is so that you can match legacy light sources like mercury vapour and fluorescent lighting. However, double and triple glazing gives us colour shift problems too when we are mixing light sources.

Take a look at this video where I show you the colour of light through glass.

Primary and Secondary Colors of Light

The primary colours of light are Red, Green, and Blue (RGB). When these colours are mixed together in various ways, they create different colours. This process is known as additive colour mixing.

When two primary colours of light are combined, they create a secondary colour. The secondary colours are Cyan (green + blue), Magenta (blue + red), and Yellow (red + green).