When you walk on a sunny day, you can see your shadow. As children, we played with shadows and thought about why our shadows followed us. Isn’t it? Usually, we have seen shadows in black colour on a lighter wall or background. Have you seen coloured shadows? Do you know how coloured shadows are formed?
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What is Shadow and Why is it Black?
As per the definition of shadow, it is defined as the space where light from a light source is blocked by an opaque object. When a part of the light is blocked by the object, it results in the formation of shadow. Shadows take the shape of the object.
The shadows that we usually see are black in colour since the space blocks the light. Since the light is blocked, light cannot reach the particular area, and hence it appears dark. In reality, all shadows are not black in colour. This happens when light bounces around the obstruction of other objects. Not all shadows are black in colour, we can also see the coloured shadows at times. Let’s see what coloured shadows are and how they are formed.
Read more: Shadow formation
What are Coloured Shadows?
We know that the white colour we see is the constituent of various colours like violet, indigo, blue, green, yellow, orange, and red. We have seen the spectacular process of splitting white light into various colours through a process known as dispersion. This process is displayed using a prism. When lights of various colours strike in the same place, preferably on a surface that is white in colour, the light reflecting from that place is the sum of the lights that strike upon it. Therefore, we see different coloured shadows on the white surface with various colour combinations. This phenomenon is known as the coloured shadow.
Let us see how coloured shadows are produced using simple equipment or materials. Let us also learn the reason for the formation of coloured shadows.
How Coloured Shadows are Formed?
The retina is the main part of the eye that is responsible for focusing on the light and aiding in viewing. The retina is composed of rods and cones which help in day vision and night vision. Cones are of three types, and these cones are sensitive to red, green, and blue colours. These three colours are referred to as additive primaries of light. Using these three colours in various combinations, seven different types of colours can be produced. The seven different colours are blue, red, green, yellow, magenta, cyan, and black. Depending on the sensitivity of each cone, they pick the colours and are responsible for our colourful vision.
Green cones help to view blue, green, purple, yellow, and orange shades. Red cones aid in seeing the purple, blue, green, yellow, orange, and red shades. By using the sensitivities of the three cones of the eye, we can see a wide range of colours that are produced when colours overlap with each other. The colour sensitivity image is as shown below.
Once the light strikes the eye, each cone cell is stimulated depending upon its sensitivity. Since the wavelengths of each colour are different, each cone picks the colour according to its sensitivity. Let us understand with an experiment how to create a coloured shadow.
How to Create a Coloured Shadow?
This simple experiment will let us understand how coloured shadows are created using primary colour-producing sources (light bulbs). This experiment is to be conducted in a dark room.
Materials Needed:
- 3 light bulbs – green, red, and blue
- A white background
- A couple of objects
Method:
- Set the bulbs in such a way that the lights fall on the same area of the white screen.
- Turn on all the lights and adjust the positions of the bulbs till you get the bright and whitest light on the screen.
- Place any narrow opaque object close to the screen, and adjust the distance until you see three distinct colours (green, blue, and red) on the screen.
- Turn off one of the coloured lights and remove the object. You can clearly observe the changes in the colours. Place the object again and observe the coloured shadow change.
- Now, try to move the object closer to the screen and see how shadows overlap. Here the combination of colours can be witnessed.
- For example: try to block two colours of lights, you can then witness the shadow of the third colour.
Try These Combinations:
- If you block the green and red colour lights, you get a blue shadow.
- If you block all three lights, you get a black shadow.
- If you block one of the three lights, you obtain a shadow which is a combination of the remaining two colours.
- If you mix blue and green colours, you get cyan colour.
- If you mix blue and red colours, you get a magenta colour.
- If you mix green and red colours, you get a yellow colour.
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Frequently Asked Questions – FAQs
In a coloured shadow experiment, when you block all three (red, green, and blue) lights, which colour do you get?
If you block all three lights, you get a black shadow.
What is a shadow?
It is the space where light from a light source is blocked by an opaque object.
Which colour is obtained when you mix blue and green colours?
If you mix blue and green colours, you get cyan colour.
Name the light receptors of the eye.
Can shadows overlap?
Yes, shadows can overlap.
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