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Light is a form of electromagnetic energy that travels through space. Light-sensitive animals, such as humans, use it to see and understand the world around them. Although the lights appear to be unique, they are actually just another form of electromagnetic energy similar to microwaves and radio waves. As it rushes through the earth, light generally travels in straight line beams and reflects and refracts in highly exact ways. Because objects have already been refracted, the majority of the light we see with our eyes is relatively low. Light beams created by lasers, on the other hand, are hyper focused and powerful enough to slice through metals.
Radiation can also be made up of photons, which are energy particles or packets. The visible portion of the electromagnetic spectrum is light. When a prism is used to supply white light from the Sun, it contains all of the visible wavelengths of energy that can be seen. Light, like all other kinds of electromagnetic radiation, can be reflected, bounced back, and refracted in a variety of ways. Vibrating particles of warm or hot things can produce visible light and infrared radiation.
Light
Light, often known as visible light, is a component of the electromagnetic spectrum that exists between radio waves and gamma rays. The fluctuations of magnetic and electric fields that transmit energy from one area to another are known as electromagnetic radiations.
The only difference between visible light and other regions of the electromagnetic spectrum is that visible light can be detected with the naked eye.
A stream of photons – massless particles travelling at the speed of light with wavelike qualities – is characterised as electromagnetic spectrum radiation. The smallest amount of energy that can be transmitted is a photon.
Between the larger wavelengths of infrared waves and the shorter wavelengths of UV rays, visible light has wavelengths ranging from 400 to 700 nm (nano-metres) or 4 ×10-7 m to 7 × 10-7 m. A frequency range of roughly 430-750 terahertz corresponds to a wavelength of 400-700 nm (THz).
Properties of light
The following are the primary properties of light:
- It has a propagation direction.
- Light comes in a variety of intensities.
- The wavelength spectrum of light has a certain frequency.
- Light can be polarised.
- In a vacuum, the speed of light is 3 ×108 m/s.
- When light travels from one medium to another, its frequency remains constant at all times.
Measurement of light
The following are the two sets of units used to measure light:
- Radiometry: It focuses light power measurements at all wavelengths.
- Photometry: It takes measurements of light using a wavelength-weighted model of human brightness perception. It’s useful for calculating the amount of illumination (lighting) intended for human use.
Units of Light
The following are the three primary types of light units:
- Candela = Measurement of Luminous Intensity
- Lumen = To calculate the Luminous Flux
- Lux = used to measure Illuminance
Candela
The SI unit of light intensity is the candela. It is the luminous output per unit solid angle emitted in a certain direction by a point light source. It’s measured in cd/m2.
Luminous intensity, on the other hand, is similar to radiant intensity. Rather than summing up the contributions of each wavelength of light in the spectrum of the sources, the standard luminosity function is used to weigh each wavelength’s contribution.
The visible spectrum frequency chosen is near green, corresponding to a wavelength of roughly 555 nm. If the human eye is adapted for bright settings, it is particularly sensitive near this precise frequency. According to the frequency response of the human eye, at other frequencies, much greater radiant intensity is required to achieve the same luminous intensity. The following is the luminous intensity for light of wavelength:
Iv (λ)=683.002 lm/W.y (λ). le (λ)
Where
Iv (λ)= Luminous intensity
y (λ)= Photopic luminosity function
le (λ)= Radiant intensity
If there are many wavelengths, the overall luminous intensity must be calculated by integrating over the spectrum of wavelengths.
Lumen
The SI unit for luminous flux is the lumen, which measures the rate at which visible light is emitted from a source. Luminous flux varies from radiant flux (power) in that radiant flux encompasses all radiated electromagnetic waves, whereas flux is measured as a luminosity function of sensitivity to various wavelengths visible to the human eye.
The lumen is defined as follows in relation to the candela:
1lm = 1cd · sr
Here,
lm= Lumen
cd = Candela
sr= Steradian
A light source that radiates one candela in all directions has a total luminous flux of four steradians, and a complete sphere has an angle of four steradians.
1 cd x 4 π sr = 4 π cd x sr = 12.57 lumens
Lux
The SI unit for illuminance and luminous emittance is the lux. It is equal to one light per square metre and measures flux per unit area. The lux is a measurement of the amount of light that passes through or impacts a surface in photometry.
When a given amount of light is dispersed over a comparatively larger area, the surface is illuminated more dimly. As a result, we can conclude that illuminance is inversely proportional to area when the luminous flux is constant. The lux is connected to the lumen in such a way that one lux equals one lumen per square metre, and is expressed as:
1 lx= 1 lm/m2 = 1 cd.sr/m2
Conclusion
The electromagnetic radiation that can be recognised by the human eye is referred to as light. Electromagnetic radiation has a wide range of wavelengths, ranging from gamma rays with wavelengths less than 110-11 m to radio waves with wavelengths measured in metres. The wavelengths visible to humans occupy a very small band within that large spectrum, ranging from around 700 nanometres (nm; billionths of a metre) for red light to roughly 400 nm for violet light.
Because light is not a physical quantity, measuring it does not appear to be practical. However, light has a variety of physical attributes such as wavelength, intensity, and speed, which can be quantified in lux, lumens, and candela. As a result, the physical properties of light can be used to approximate its measurement.
