What is the colour of light
In the last post we talked about the properties of light, today we are going to look at “What is the colour of light?” No pun intended, ok maybe a little bit. You are probably wondering why we are spending so much time on this stuff? The reason is that in order to take great pictures you need to understand clearly why you are not getting the results you had hoped for.
Yes, all the technical information that we have covered and will be covering in greater detail is important. But the human element, how we handle our equipment, how we align things compositionally, and finally how we see a scene is the most important,
The electromagnetic spectrum
Light is energy that travels through space at a rate of 186,000 miles per second and comes in a packet called a photon. Each of these photons travels in a wave that is seen as a different colour depending on the length of the wave it is travelling on.
We all know that the light coming from the sun is a rainbow of colour, but we see it as white. Within this ray of light, there are many types of light in the forms of various wavelengths. From the illustration above you can see a variety of them. We can only see what is called the visible light spectrum. Red has the longest wavelength and each colour gets shorter from there: orange, yellow, green, blue, to one of the shortest violet.
What happens when the light gets absorbed or refracted?
A good example would be, “Why is the sky blue?”
The atmosphere is full of various water and gas molecules. These molecules cause the incoming sunlight to be scattered or redirected. We have talked about the length of the wave and now know that blue has the shortest length and the others are longer with red being the longest. This means that blue is easier to scatter than the red so the blue is scattered all over the place and the other colours get through to the surface and we get to see the sky as blue.
At the other end of the spectrum, why is water blue? Water absorbs warm colours which are long wavelength light and scatters the cooler colours (short wavelength light). Red light is absorbed strongly, and the blue light has the deepest penetration depth. That’s why we get blue water.
The opposite occurs early in the morning and at sunset. The shorter red wavelengths hit our eyes because they are not scattered while we don’t see the blue wavelengths because they are scattered. What we see are beautiful warm orange/red sunrises and sunsets.
How do we see colour?
White light consists of blue-violet, green, and red, when these are all mixed together they produce white light. These are known as the primary colours. True enough, when an artist works with pigments and mixes these together they are far from white. But we are working with transmitted, reflected, dispersed, refracted, and absorbed and when the primary colours are used in this way they mix together to make white light. In our investigation of light, it is the absorption of colour that we are concerned with. It is the absorption of light that make the colour. Objects will absorb, transmit, or reflect light falling upon them. We cannot see the light that is absorbed, only that which is reflected.
This brings us to the next concept in light, that which is called Colour Temperature
We need to understand that the colour of light is not consistent because of the dispersion of the wavelengths at a different time of the day or the light source that you are using to take pictures with. As we saw with blue skies and sunsets the amount of the various wavelength being scattered caused the colour we see. Similarly, light sources have a variety of wavelengths in their chemical makeup that changes how a camera will record the colours. The eye does not see how a camera sees. In our brain, we have recorded what colours should look like and when we process the scene we will see it as we think we should see it. For example, a white shirt in bright sunlight will be white, but under tungsten light it is orange, and under fluorescent light it is green. All the while the brain tells us that it white and we see it as white.
The need for an accurate means of measuring the colour of the light was realized by the English scientist, Lord Kelvin. When you put an iron poker into a fire it first turns a dull red and then glows to a brilliant red and finally turns white. Lord Kelvin produced this effect and standardized it and then identified the colours by the temperature of the metal at that instant. The temperature is described as Kelvin degrees.
This is the point where you can say to yourself, no wonder when I take pictures inside the colours are wonky. Or on the opposite extreme, when you see a fantastic sunset and you take a picture of it the colours are not as vivid as you “see” it.
Your camera has a variety of settings that control or allow various colour balancing. Several of the common symbols for these options are seen below:
“AWB”, or auto white balance is the standard go to. It automatically tells the computer to reproduce the colours to make it look like the picture was taken at high noon – 5500 k. So, the nice glow of the fireplace on the kids’ faces or that vivid sunset is lost with the AWB.
“Custom”, allows you to set your own white point. The best way to do that is to use a “Gray card”. A grey card is a photographic card that is covered with a neutral grey set at 18% on the gray scale. A grey scale is a scale that goes from white through various stages of grey all the way to solid black. White has a value of 255, while black has a value of 0, and the greys have a value in the middle.
All light meters are set up to take a recording of the light as if it were looking at a 16% grey patch. We will discuss reading light in another post. Because if you think of it logically, when you are taking a picture of snow and the light meter is thinking that it is looking at 16% grey, your picture will look muddy, or at least grey, lol.
Why do they use a grey card? Because when you use a grey card it is easier to see slight colour, tonal, and contrast shifts.
Back to our grey card. Take a picture of the grey card in the sunshine between 11:00 am and 1:00 pm and save it on your camera. Make sure that the card is evenly lit. Use the automatic setting. Fill the screen with the grey card.
For Canon users:
- Find the “custom” setting in your colour balance menu and it will ask you to choose an image.
- Choose the image you just took of your grey card and choose “Ok”.
For Nikon users, the custom setting is actually called “Pre” for Pre-set Manual White Balance setting.
- Set your camera to the automatic exposure mode
- Fill the viewfinder with your grey card
- Select white balance, press ok
- Select PRE, press the Multi Selector right,
- Select Measure, press OK
- Select Yes and press OK
for other camera makes and models look in your instruction manual.
Although it takes a bit more thinking, using Kelvin is much easier the more you use it. Not to forget that you will get the results that you are aiming for. Basically, memorize the “Colour of Light” chart above and set your Kelvin setting to the temperature of the light you are working with. If you are photographing with candles you would be around 2000K, outside in the sunshine 5500K, in the shade approximately 7000K. Those are rough parameters. Another way to think about it would be; if you want cooler colours to go higher up the scale 7000K – 9000K, if you like warmer pictures 2500K – 4000K. As mentioned back in one of our earlier posts – you are in control of your image. Make sure that what you see is what you will get or create.
This setting is the one you would use when taking pictures in your home when you have tungsten bulbs in your lamps. Tungsten bulbs are the old fashioned normal light bulb that is a yellowish/orange colour.
Fluorescent lights have an ugly green, cool colour. You would use this setting to get rid of that shade.
This may sound silly but daylight means you are using pure sunlight and are away from shady, or areas that would get a colour cast reflected from grassy area or buildings.
Naturally we are talking about an overcast, cloudy day that offers a cool colour. This will warm up the image for you.
Each flash unit has a colour temperature of its own, but usually they are considered “cool” colours. So this setting will warm it up for you.
We come to the last option, shade. Shady areas often are cooler and have tinges of green or the colour of the object that is creating the shade. Once again we see a warming effect.
AWB Kelvin 5,000 Kelvin 2,000
indoors it would look good indoors it would look good
blue removed yellow removed
Tungsten setting Fluorescent Daylight
yellow/orange removed red/green removed
Cloudy setting Flash Shade – some blue removed
We hope this will help you get the images that you imagined and deserve.
Good shooting and pure colours!
Bob and Chuck
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