What is Light? – Part 1


When we first learn about light, we see very simply the world is either light or dark. There is day and night and there are little switches on walls that turn indoor light on or off. Soon, we learn that the Sun is the source of all natural light and things quickly become more complicated. Light from the Sun travels to our planet after a speedy trip of 149 million km. Light travels at an average speed of 300,000 km per second. We can detect the light originating from the Sun in approximately 8 minutes. In other words, it takes a little over 8 minutes for light energy from the sun to travel to us.


The Sun is an enormous fireball shooting energy in all directions. When light travels between two places (from the Sun to the Earth or from a flashlight to the wall in a dark room), light energy makes a journey from the light source to a receiving object in the form of waves (light waves or electromagnetic waves). These are similar to waves traveling in the ocean but millions of times smaller in a vibrating pattern: electromagnetic energy.

The Problem

Colour is one of the hardest concepts of understanding light.
Sunlight isn’t light of just one colour — it’s what’s called white light or a spectrum of light that is made up of many different colours. Evidence of this is seen in a Rainbow. Rainbows are colourful curves of light that appear in the sky when droplets of water split sunlight into different component colors by refracting (bending) sunlight by differing amounts. Components of light are bent into different wavelengths producing different colours. Light that we observe from the sun often appears ‘white’ or colourless but it is made up of several colours in the colour spectrum.

Sample Problem

What is light? What is this light energy, visible light or spectrum that is detected by our eyes?


Light Spectrum Experiment


4 small flashlights
durable plastic wrap
coloured paint or nail polish (red, green, blue)
flat white surface to shine light (must be in a space or room that can be darkened)


1. Shine light onto the flat white surface in a darkened room. Observe. Record.

2. Paint 3 plastic wraps 3 different colours. Surface area must be enough to cover the glass light of the flashlights. Tape the coloured plastic covers onto the glass surfaces of the 3 flashlights with the 3 different colours. You should have one red coloured flashlight, one green coloured flashlight and one blue coloured flashlight.

3. Shine each coloured light onto the flat white surface in a darkened room. Observe. Record.

4. Now, combine the 3 coloured lights onto the same spot on the flat white surface. Observe. What colour is observed with all 3 lights shining on the same spot? Record.

Optional question:

5. Is combining 3 light sources together the same as mixing 3 paints together? This is an extended question for a future experiment.

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