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Lighten up!

Welcome to the second in our blog series introducing the science behind some of the new interactives to be revealed when the Tūhura Otago Community Trust Science Centre opens in December. Here, Science Communicator Catriona Gower sheds some light on light!

An absence of light means everything appears completely dark, effectively black, yet light is not simply white. Nor is it grey! So what is it?

Let’s start at the beginning, and the source of all our energy: the sun. The sun floods us with light and heat (forms of energy) that all life on Earth depends on. The sun produces this energy with a whole range (or spectrum) of wavelengths. Some are so incredibly small that they are measured in picometres (pm), where one picometre is just one thousand of a nanometre (nm), which is itself a millionth of a millimetre (mm). Others are so long that they are measured in kilometres; that’s quite a range! 


Lighten up tuhura

Source: AP Chemistry: Electromagnetic Radiation  


The longer the wavelength, the less energy it has. Very long wavelengths include radio waves and microwaves, neither of which we can see.

At the other end of the spectrum, the shortest waves have phenomenal levels of energy, making them really dangerous to living things. This wavelength is also known as gamma radiation.

Not quite as small, but still harmful to us because they have so much energy, are x-rays and ultra violet (UV) waves. These are measured in nanometres (remember, 1 nm is 1 millionth of a millimetre – so, still very short wavelengths!) In the summer, we protect ourselves from UV to reduce our chances of developing skin cancer.  We can’t see any of these wavelengths either!  So what do we see?

Together, all the wavelengths of energy that radiate from the sun are called Electromagnetic Radiation (EMR). The visible light we see is a tiny part of this EMR spectrum. Humans can only perceive wavelengths from about 400 nm to 700 nm. In a rainbow, the many colours we see are the whole merging spectrum of wavelengths between 400 nm and 700 nm. Our eyes see each as a different colour. At 400nm it looks blue, 550nm it is green and 700nm it is red. 

I have only picked these three wavelengths as these are three that match up to three types of cells in the retinas of our eyes. These colour-perceiving cells are called ‘cone cells’. Selectively, one set of cone cells is sensitive to blue wavelengths, another to green and another to red. By blending relative amounts of these three colours, our brain cells are able to distinguish a million or more hues of colour, and to make (perceive) pure white light! Some animals, including butterflies, have four or more different types of cone cells and can perceive those wavelengths invisible to us. Most often they are able to see UV. 

So what happens when some colour wavelengths are missing? Red and green without blue produce yellow! Remove only red wavelengths from the mix and you have cyan (turquoise). You may recognise some of these colour combinations from around your house – did you connect up some RGB leads to give you colour images? Or did you buy new inks for your printer in cyan, magenta and yellow? It can be fun experimenting with lights of just one or two colours together.

In Te Ao Māori all exists together; the past, the future, the present, and every part of this world as it is. Apply this view to EMR: white light, and all that it allows us to see, is only possible through a combination of red, blue and green wavelengths. We cannot see all of EMR, but all the wavelengths exist, affecting our world, and other living things may be enjoying those wavelengths we are oblivious to.

Come along to Tūhura when it opens in December and see the light!