Light

When we look at a leaf, we can tell that it is green because light bounces off the leaf and into our eyes, signalling to us that the leaf is indeed green. But what exactly is light? What are the sources of light that are responsible for the creation of light? Radiation of the electromagnetic spectrum is known as light. The human eye can detect a specific frequency of this radiation (around 390-700 nm) because of its wavelength. Everything that we can see in our environment is due to the presence of light. 

EM spectrum; Visible light

Electromagnetic Radiation (EMR) is generally classified by wavelength, with radio waves being the most common. Microwaves and infrared are the most common, and the visible spectrum (which we perceive as light) is the most common. Static electric, magnetic, and near-field fields are not included in the definition of “radiation.” The behaviour of EMR is determined by the wavelength it emits. The wavelengths of higher frequencies are shorter, while the wavelengths of lower frequencies are longer. When electromagnetic radiation (EMR) interacts with single atoms and molecules, the behaviour of the EMR depends on the amount of energy carried by each quantum it contains.

Electronically excited molecules (EMR) in the visible light range are composed of quanta (called photons) with energies that are at the lower end of the range of energies capable of causing electronic excitation within molecules, which results in changes in the bonding or chemistry of the molecule. Because its photons no longer have enough individual energy to cause a lasting molecular change (a change in conformation) in the visual molecule retinal in the human retina, EMR becomes invisible to humans at the lower end of the visible light spectrum (infrared). This occurs because the photons no longer have enough individual energy to cause a lasting molecular change (a change in conformation) in the visual molecule retinal in the human retina, which triggers the sensation of vision.

Speed of light

According to scientific definitions, the speed of light in a vacuum is exactly 299 792 458 metres per second (approx. 186,282 miles per second). Given that the metre is now defined by reference to the speed of light, a fixed value for light’s travel time in SI units has been established as a result. 

Throughout history, physicists have attempted to determine the speed of light in various configurations. In the seventeenth century, Galileo attempted to measure the speed of light with a telescope. Ole Rmer, a Danish physicist, conducted an early experiment to measure the speed of light in 1676, which was the first time this had been done. Taking into account discrepancies in the apparent period of Io’s orbit, he calculated that light takes approximately 22 minutes to traverse the diameter of Earth’s orbital diameter. However, the exact size of the structure was unknown at the time.

Types of Light Sources

Even though there are many different types of light sources, each of them falls into one of the two categories listed below.

• Natural sources of light
• Artificial sources of light

Natural Light Sources:

The universe is teeming with objects that radiate light in all directions. Every other star also emits light, but due to the vast distance between them, only a small or insignificant amount of it reaches the earth.

The moon also contributes to illumination, but it is unable to generate light on its own. Our experience of the moon is primarily a result of the light that it reflects back to us from the sun.

Some living organisms are also capable of generating light in their own right. In the body, it is the result of certain chemical reactions occurring within the body. Fireflies, jellyfish, glow-worms, certain deep-sea plants, and microorganisms are examples of organisms that glow in the dark.

Other natural phenomena, such as lightning and volcanic eruptions, produce light.

Artificial Light Sources:

Light can be produced artificially in addition to coming from natural sources. Generally speaking, the different types of artificial light sources can be divided into three broad categories:

Incandescent Sources:

Light is produced when certain objects are heated to a high temperature and then allowed to cool. The process results in the production of both infrared and visible light.

For instance, a candle or an incandescent lamp.

Luminescent Sources:

A luminescent material can emit light when charged particles accelerate in the presence of an electric field. Passing current through the material is a common method of accomplishing this goal.

For instance, fluorescent tube lighting and electric bulbs are both examples of lighting.

Gas Discharge Sources:

Passing electricity through certain gases at extremely low pressure can also result in the production of light.

Conclusion

Visible light, is radiation that falls within the portion of the electromagnetic spectrum that is visible to the human eye. For the purpose of this definition, electromagnetic radiation of any wavelength, visible or not, is referred to as “light” in physics more broadly. In this sense, gamma rays, X-rays, microwaves, and radio waves are all considered to be light. One of the most important characteristics of light is its intensity. This particle’s speed in a vacuum, which is 299 792 458 metres per second (m/s), is one of nature’s fundamental constants. Visible light, like all types of electromagnetic radiation, is propagated by massless elementary particles known as photons, which represent the quanta of the electromagnetic field. Light optics, as it is known in the scientific community, is a significant research area in contemporary physics. The Sun is the most important source of natural light on the planet. Fire has always been a significant source of illumination for humans, from ancient campfires to modern kerosene lamps, and has been for thousands of years. Electric lighting has largely taken the place of firelight as a result of the development of electric lights and electrical power systems.