Ways of thinking about light
From the time of the ancient Greeks, people have thought of light as a stream of tiny particles. After all, light travels in straight lines and bounces off a mirror much like a ball bouncing off a wall.

The idea of the light wave came from Christian Huygens, who proposed in the late 1600s that light acted like a wave instead of a stream of particles. In 1807, Thomas Young backed up Huygens’ theory by showing that when light passes through a very narrow opening, it can spread out and interfere with light passing through another opening. Young shined a light through a very narrow slit. But that was not all he saw. Young also perceived additional light, not as bright in areas around the bar. If light were a stream of particles, this additional light would not have been there. This experiment suggested that light spread out like a wave. In fact, a beam of light radiates outward at all times.

Albert Einstein advanced the theory of light further in 1905. Einstein considered the photoelectric effect, in which ultraviolet light hit a surface and caused electrons to be emitted from the surface. Einstein’s explanation for this was that light was made up of a stream of energy packets called photons. 

What is light?
To understand light waves, it helps to start by discussing a more familiar kind of wave – the one in the water. One key point to keep in mind about the water wave is that it is not made up of water. The wave is made up of energy travelling through the water. If a wave moves across a pool from left to right, this does not mean the water on the left side of the pool is moving to the right side of the pool. The water has actually stayed roughly where it was. It is the wave that has moved. All waves are travelling energy, and they are usually moving through some medium, such as water. Light waves are a little more complicated, and they do not need a medium to travel through. They can travel through a vacuum. A light wave consists of energy in the form of electric and magnetic fields.

Natural Light
Light from the Sun brings energy to Earth – energy that can be absorbed by plants for photosynthesis, by oceans to evaporate water and cause rain, by photocells and solar panels to create electricity, and so on. When light enters the human eye and falls on the retina, it sets off photochemical and neurological processes that result in seeing. Radio waves, television transmissions, microwaves, ultraviolet light, X-rays are all forms of electromagnetic waves just like light, but with a different wavelength. The human eye cannot perceive these wavelengths, but instruments can pick them up.

Hanukkah
Hanukkah is often included when teaching light as a topic. It is more usual for this to be done in Key Stage 1. Hanukkah, which means ‘dedication’ and is also referred to as ‘Festival of Lights’, is a Jewish festival, which begins on the Hebrew date of the 25th of Kislev and lasts eight days, through the 2nd Tevet.

Hanukkah commemorates the victor of the Maccabees (led by Judah) over the Hellenistic Syrians in a revolt that took place around 165BCE. The victory itself was considered a miracle, but Jewish legend gives an additional explanation for Hanukkah rituals. Once the Temple Mount in Jerusalem had been reclaimed the Temple had to be rededicated. According to legend, only one jar of sacramental oil was found, enough for one day. Miraculously, the oil burned for eight days, thus the eight days of Hanukkah.

The most important Hanukkah ritual is the candle lighting. Jews light candles in a special candleholder called a ‘menorah’ or a 'hanukkiah’. Each night one more candle is added. The middle candle, called the ‘shamash’, is used to light each of the other candles and it is lit every night. Therefore, on the first night of Hanukkah, two candles are lit (the shamash and the candle for the first night) and on the last, there are nine lit candles. 

Diwali
Looking at the celebration of Diwali is a common introduction to Hindu beliefs and practices at Key Stage 2. Telling the story of Rama and Sita is a useful starting point to help pupils understand why lights are an important focal point in all Diwali celebrations.

The festival of Diwali has existed from the time immemorial, ever since man became aware of the truth and untruth, darkness and light, death and immortality. Diwali is the Festival of Light. Hindus celebrate it all over the world.

The true meaning of Diwali can be expressed as being to bring light where darkness prevails, truth where untruth prevails, to bring life where death prevails, to brighten our surroundings, to illuminate our minds.

The Festival signifies the triumph of light over darkness, good over evil, justice over injustice and intelligence over ignorance. The goddess worshipped at Diwali is Mother Lakshmi or Lakshmi Mata, the goddess of light, wealth and beauty and is also associated with prosperity, luck, riches, abundance, financial well-being and generosity.

Teaching about light and dark

Understanding the theory of light and the enormous impact it has in every context is as important in the 21st century as it ever was. To support the teaching of the topic, access an exhaustive bank of project plans for each core subject, complete with teacher guidance, photographs, illustrations, information sheets and activity sheets below. Projects include rainbow poetry, coloured shadows, photosynthesis, festivals of light and the history of light and kaleidoscopes.

Download Light and Dark Project Plans:

Light and Dark Science Project Plans