Aim: I want to find out how to mix colours made of light and how coloured light is made.
Research:
How is coloured light made?
Light itself is made up of wavelengths of light. These wavelengths are all a particular colour. The colour that we see is the result of which coloured wavelengths are reflected back to our eyes. When coloured lights are mixed together it is called additive mixing. The primary colours for additive mixing are red, blue and green. If all of these colours are shone onto a screen the colour will be white.
(nm stands for nanometre, or a billionth of a metre.)
What is white light?
White light contains all of the colours of the rainbow (red, orange, yellow, green, blue, indigo and violet). This is because it contains all wavelengths and it is described as poly-chromatic light. A specific colour can be defined by a range of tiny wavelengths in nano metres. Visible light is the small part within the electromagnetic spectrum that the human eye can detect.
Light from a source such as a laser, is described is monochromatic. This is because it only produces a single colour.
The colour of objects
Objects can often appear as different colours. This is because they absorb and reflect or transmit some colours. The wavelengths/colours we see are the colours that are reflected or transmitted. An example of this would be: A red shirt. The reason it looks red is because the dye molecules in the fabric have absorbed the wavelengths of light from the violet and blue end of the colour spectrum. Red light is the only light that is reflected from the shirt. If only blue light is shone on the shirt, the shirt will appear as black, because the blue light would be absorbed and there would b no red light to be reflected.
White objects appear as white because it reflects all colours, where as black objects appear as black because they are absorb all colours, therefore no colour is reflected.
How does the human eye detect colour?
The retina (A light sensitive piece of tissue that lines the bag of your eyeball) of our eyes contains two types of photo receptors- rods and cones. The cones detect colour, and the rods only allow us to see black, white and grey. Our cone photo receptors only work when the light is bright enough and not when it is dim. This is why things look mostly grey to us during the night time.
Mixing Colours
As I said before, the primary colours of light are red, green and blue. when you mix these colours together in all sorts of different proportions, you get all the different colours of light that are visible to the human eye. This is actually how TV, computer and phone screens work. If you were to look at your TV at home through a magnifying glass, you would find that the only three colours used to make the picture are blue, red and green. They use different colour combinations with different proportions to trick our eyes into perceiving completely different colours.
Autochrome Lumiere
The Auto chrome Lumiere is an early colour photography process. Created in 1903 by the Lumiere brothers in France and first marketed in France in 1907 and was the first principal colour photography process used before the discovery of subtractive colour film in the mid-1930's. Auto chrome was an additive "mosaic screen plate". The middle of this peculiar thing was coated on one side with a random mosaic of microscopic grains of potato starch, dyed red blue and green (an unusual but very effective piece of equipment). These acted as colour filters. The spaces between the grains were black and a black-and-white panchromatic emulsion is coated on top of the filter layer.
This is the light box that we used for our experiment:
Experiment:
For my experiment, I am going to use a light machine and filters to mix colours, and take photos of the results to see how accurate the additive mixing wheel is.
Equipment:
To do this yourself you will need:
- A light box (If you can not find one you could also use three lights and a mirror)
- Different coloured pieces of plastic to put in front of the lights
- A dark room and something white to shine the light on
What to do:
It is very easy to do this experiment. All you need to do is put your light box (or what ever you are using as an alternative) in a dark room, the front light faced towards a white wall or other white object. Then put different coloured pieces of plastic in front of the lights and move the mirrors until they all point towards the same place, then the colours will mix.
Green and Red= Yellow Correct
(It is slightly hard to tell on camera, but the colour in the middle is yellow
Blue and Green= Cyan Correct
Blue and Red= Magenta Correct
Green,
Red and
Blue=
White Correct
(again not very clear on camera, but the middle colour is a slightly tinted white)
Here is another filter which made stripes of different colours when mixed with other filters.
Explanation:
Our experiment was very successful. There was only one filter (the yellow one) that didn't work, because when you mixed it with others it still over powered the other colours. If I did it again, I would probably use a better background to shine the colours at.
So why did it work? The colour that we see is the result of which coloured wavelengths are reflected back to our eyes. When they mix together, some coloured wavelengths are absorbed and others are reflected. This is how light mixes to make other colours.
What went wrong?
We did have to find a different room, as the first one we used was too bright. In the new room we also had to point the light box at the roof so it appeared
clearer and brighter.
