The Electromagnetic Spectrum
There is far more light around us than we can see. We usually think of light as the colours of the rainbow, but visible light is actually only a tiny section of a much larger thing called the electromagnetic spectrum.
The spectrum is essentially the full range of electromagnetic radiation, arranged according to wavelength and energy. And once we discovered and understood the implication of it, out came the creativity and ingenuity of humans, creating innovations that utilised the waves of the spectrum.
A Spectrum Of Energy
At the long wavelength, low energy end of the spectrum are radio waves. Then come microwaves, infrared, visible light, ultraviolet, X-rays and finally gamma rays at the short wavelength, high energy end.
There aren't clear boundaries between all of these. They gradually change from one wavelength to another, rather like the colours of a rainbow blend into each other. Visible light is simply the small section that our eyes are capable of detecting.
How Did We Discover It?
The story begins with our understanding of light and colour.
In the seventeenth century, Isaac Newton conducted an experiment where he split light using a prism, into the rainbow of colours. From this he created his theories on colour and the colour wheel which is used by artists today.
Later scientists discovered that there were other forms of radiation beyond this rainbow of colours that made up visible light. We just couldn't 'see' them with our eyes but it doesn't mean that it isn't there.
In 1800, William Herschel discovered infrared radiation when he measured the temperature beyond the red end of the visible spectrum. A year later, Johann Wilhelm Ritter discovered ultraviolet radiation beyond the violet end. X-rays were discovered by Wilhelm Röntgen in 1895. Radio waves were experimentally demonstrated by Heinrich Hertz in the late nineteenth century.
What appeared to be separate phenomena were gradually revealed to be different parts of the same electromagnetic spectrum.
Why Does It Matter?
Understanding the spectrum completely changed what humans could do.
Radio waves gave us wireless communication. Microwaves became important for communication, radar and heating. Infrared can be used for thermal imaging and remote controls. Visible light allows cameras, screens and optical instruments to work. Ultraviolet is used for things such as sterilisation. X-rays allow us to look inside the human body without cutting it open. Gamma radiation has applications in medicine and scientific research.
It also allowed us to understand other species and how they interact with their environments. Some species are capable of detecting infrared or ultraviolet energy and that helps them to navigate their environments, find food and protect themselves from predators.
The electromagnetic spectrum therefore isn't just an interesting scientific diagram. Modern society depends on our ability to understand and manipulate different parts of it.
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