Seasons
January 28, 2020
Time
January 29, 2020
  • Light is an electromagnetic radiation. A particular frequency of this radiation (around 390-700 nm) is visible to the human eye.
  • Light is a form of energy and like all energies, it is produced from a source.
  • In physics, these are called Light sources.


Types of light sources:

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Natural Light Sources:

The universe is filled with objects that emit light. Some of the light from these sources reach the earth. The following things in nature have the ability to emit light:

Natural Light Sources Description
SeasonsThe Sun
1. The Sun is the major source of light for the earth.
2. The sun is a massive ball of fire, at the centre of which nuclear fusion produces massive energy.
3. This energy comes out as heat and light.
SeasonsStar
1. Every star produces light.
2. Only a small or no amount of it reaches the earth because of the huge distance.
SeasonsThe Moon
1. The moon provides light as well but it cannot produce light on its own.
2. The light that we get from the moon is the light reflected by it from the sun.
SeasonsLiving Organisms
1. Some living organisms have the ability to produce light too. It is called bioluminescence.
2. It is the effect of certain chemical reactions within the organism.
3. Fireflies, jellyfish, glow worm, certain deep-sea plants and microorganisms can be cited as examples.
SeasonsVolcanic Eruptions
1. Certain other natural phenomena such as lightning and volcanic eruptions also emit light.


Artificial Light Sources:

Apart from the natural sources, light can be produced artificially too.

Artificial Light Sources Description
SeasonsIncandescent Sources
1. When certain objects are heated to a high temperature, they begin to emit light.
2. Both infrared and visible light is produced in the process.
3. Example- Candle, incandescent lamp.
SeasonsLuminescent Sources
1. Light can be produced by accelerating charges in a luminescent material.
2. One common way of doing it is by passing current through the material.
3. Example- Fluorescent tube light, electric bulb
SeasonsGas Discharge Sources
1. Passing electricity through certain gases at a very low pressure can produce light too.
2. Example – Neon lamp, Sodium lamp.


Light Pollution:

Unwanted extra light from artificial sources is referred to as light pollution. Light pollution exists in four different forms:

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1. Glare: This is when a light that is too bright often causes glare, or a visual discomfort, when looking at the light.

2. Skyglow: This is when too many external artificial lights cause the night sky to glow. You can see this when looking down at a well-lit city. The sky above the city is brightened.

3. Light trespass: This is when a big, bright light shining on one area usually intrudes and shines on unwanted areas.

4. Clutter: This is when you have too many lights bunched up together or when the lights are grouped in confusing ways, and it can make you dizzy or confused looking at them.


Effects of Light Pollution:

While many people choose to dismiss light pollution as being the price of modern life, it has serious effects on everything around it.

  • Animals – Lights can attract or repel animals and insects. This can place entire species in danger, or attract unwanted species into human areas.
  • People – The wrong kind of light, or too much light has been proven to have an impact on your health and quality of life.
  • The Earth – The Earth’s ecosystem is dependent on cycles of natural light. This disrupts growth and decay cycles that our food, air and water supply is dependent on.


Interesting Facts:

  • A ray of light travels very fast. The speed of light in space is approximately 300 million metres per second.
  • A mirror has a very smooth surface. When a mirror reflects a ray of light the angle of incidence is always equal to the angle of reflection
  • Some objects appear coloured. They reflect certain colours of white light and absorb the other colours. The light reflected to the eye is the colour you see.
  • A shadow happens when an object blocks the sun’s rays. Shadows are longer in the winter because of the angle of the sun.
  • Some animals are nocturnal. They are awake at night. These animals usually can see very well in the dark. Our eyes aren’t designed to see well at night.
  • Black or dark objects absorb light and heat. White or light objects reflect it. During the summer, you’ll stay cooler if you wear light clothing.
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