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In this exhibit you learn about how the colours we see depend on the light conditions.
In order to see colour we need light. Specifically, we need light the same colour as the colour we're trying to see.
Natural sunlight and most indoor light bulbs produce white light. White light is made up of all the different colours of the rainbow, so under white light we can see all the colours.
Under coloured lights, however, objects appear to be the same colour as the light, or may appear black.
This is because objects absorb most of the light, and reflect back the colour they are. So a yellow object under white light will absorb most of the colours of light, and reflect back the yellow light, so we can see yellow.
Because yellow light is a mixture of red and green light, yellow will also reflect red and green light. This means that a yellow object will appear red under red light, and green under green light. Yellow does not contain blue, so it will appear black under blue light.
White objects reflect all light, so will appear to be the colour of the light on them. Black objects, conversely, absorb all the light, and do not reflect any, so always appear black.
Most white light also contains infra-red, which we cannot see. Infra-red is heat energy. Black objects absorb the infra-red, so get warmer when exposed to it, but white objects reflect infra-red so do not warm up. Because of this, many people wear white or pale coloured clothes in hot weather, and houses in warm places are often painted white.
You might be wondering why, if white reflects heat and black absorbs it, most people who come from hot places have dark skin, and most people from colder places (like Scotland) have pale skin. That's because sunlight also contains ultra-violet, which can burn the skin and cause cancer. Dark skin contains melanin, which protects against ultra-violet when there's lots of strong sunlight. But we need some ultra-violet to make vitamin D, which is essential for healthy bones. Pale skin helps people to get enough ultra-violet to make vitamin D when there isn't much sunlight.
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Questions
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| 1 |
In order to see colour, we need ________. |
| 2 |
What colours of light will be absorbed or reflected by a yellow object? |
| 3 |
What colour would a yellow object appear under blue light? |
| 4 |
What colour could your paint your house to keep it cool in hot places? |
| 5 |
Why is it helpful for people in Scotland to have pale skin? |
| 6 |
What other SCI-FUN exhibit looks at how colours appear under different lights? How does our brain see things under different coloured lights? |
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Activities
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| 1 |
Try looking at things through coloured filters, such as coloured glass, plastic, liquid or cellophane, or put a coloured filter over a torch. How do the colours you see differ from the normal colours? |
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Separate white light into a rainbow. Fill a glass with water and place it on the edge of a table or sideboard. Put white paper on the floor beside the table or sideboard. Put masking tape over the end of a torch so that light can only come out a tiny slit (less than 3mm wide). Turn off the lights and shine the torch onto the water at an angle. Move the torch around until you get a rainbow on the paper. |
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