There are many components to light and we humans can only observe a very narrow band of it with our naked eyes. We call this very narrow band the “visible light spectrum” for that very reason. You may be familiar with some of the other wavelengths of light listed below like X-rays and FM or AM radio, however, today we’re starting by looking only at visible light and infra-red rays.
https://qph.fs.quoracdn.net/main-qimg-45d477f26e512244e9adfb0cf4f08040.webp
You can experience light from many different sources. Spend the next 5min brainstorming in class where you might find sources of visible light energy.
Infrared Light
Now infrared light sounds like a new thing, however, it’s something that you experience everyday and you would be rather cold without it. We humans can actually feel infrared light as heat. You are constantly emitting infrared light from you’re body and into your surroundings. When you put on a jacket, you can trap the light in for a bit, but the infrared light will eventually “leak out”, depending on the thickness of the jacket and how cold it is outside.
Over time the environment will settle to equilibrium where all things in a room are at the same temperature, UNLESS, there is a way for the energy to be removed (which there usually always is… think leaky windows and open doors).
http://www.thermohuman.com/new-book-infrared-thermography-detection-injury-sports-medicine/
The image above shows how Infrared light is emmited from humans.
The more RED something is, the hotter it is and the more Infrared light it is producing.
The more BLUE something is, the cooler it is and less Infrared light is being emitted.
The pants being worn, traps in the heat, making the legs warm and without a shirt, heat is lost.
Activity: Think about how your room cools down over night, what are some things that you can do to keep the warmth in? Alternatively, during summer, how do you remove the excess Infrared light?
Visible Light
Visible light can be broken up into 3 main colours that we can see with our eyes. They are Red, Green and Blue (RGB). Right now as you look at this monitor, you are experiencing black text on a “white” background. However, what is really happening is the black is missing light and the “white” is only made of RGB.
If you look at the following colours on your screen with a drop of water on it you may just catch a glimpse of them for yourself
White
Red
Green
Blue
How and why does RBG matter?
RGB allows modern technology to produce MOST of the visible spectrum without wasting too much power on all the colours of light in-between. The Sun does not have the same “energy” problem. It instead produces HUGE amounts of Visible and Infrared Light (and several other types of light) as a side effect of burning. We use this light for many things, including Solar Panels where we can catch +20% of the light and turn it into Electricity to (rather ironically) make Visible and Infrared Light somewhere else where the sun is not shining.
Practical
Using your lux meters which are designed to measure the brightness or intensity of visible light, you will need to try and develop a method to try and see who has the brightest phone in the classroom and who has the darkest. You will need to include the following headings in your book:
Aim – what are we trying to achieve?
Independent variable – what are we going to change?
Dependent variable – what are we going to measure?
Control Variable – things that you will need to have in place to make sure that it is a fair test
Method – how will you make this work? You can use any of the equipment under the benches and your light meter. (If you need a white phone image scroll up)
Results – you might need a table and a graph to show your results
Conclusion – which phone had the brightest display? how much brighter was it?
EXTRA – If you finish this practical early, what happens when you move the sensor closer and further back near the phone? Draw up and extra graph to see if there is a linear relationship with distance and brightness.
Extension
Want to learn how light might be used to diagnose diseases on a computer the size of a 20c coin one day?
Watch the attached video and see why light matters
https://youtu.be/j7heZpuvu4U
Or, solve a crime with Infrared light using this video
Mr Danic 