When we talk about Ultraviolet light, we need to know some basics.
What is the Electromagnetic spectrum?
Radiations coming from the sun to the earth’s surface in form of energy. These radiations transmitted in waves or particles at different wavelengths. This range is known as the electromagnetic spectrum. These radiations are:
- Radio waves
- Visible light
- Gamma rays
What is ultraviolet (UV) light?
UV is a form of electromagnetic radiation. See the electromagnetic spectrum, UV range is between visible light and X-rays.
- The wavelength range of UV: 10 to 400 nm
- The frequency range of UV: 8 × 1014to 3 × 1016 Hz
- Invisible for human eyes
- Can damage living tissue
Categorization of UV light.
The UV light can be divided into the following three bands based on the band:
- UV-A: 315 to 400 nm
- UV-B: 280 to 315 nm
- UV-C: 100 to 280 nm
As per the statement of NTP, only 10 percent of sunlight is UV, and only about 3.33% of this 10% UV light reaches the ground.
The UV light from the sun to the earth’s surface is 95 % UVA, 5% UVB, and no measurable UVC.
The reason behind no UVC from the sun to earth’s surface is ozone, molecular oxygen, and water vapor in the upper atmosphere, they absorb the shortest UV wavelengths
Vacuum or extreme UV: Radiations with wavelengths from 10 nm to 180 nm. These wavelengths are blocked by air, and they only propagate in a vacuum.
Theories and Calculation
Quantum theory: The rate of the energy of one joule (J) per second is optical power (W). Optical power is a function of both the number of photons and the wavelength. Each photon carries energy can be described by Planck’s equation:
Q = hc/λ
Where Q is the photon energy (joules),
h is Planck’s constant = 6.623 x 10-34 J s, and
λ is the wavelength of radiation (m)
c is the speed of light = 2.998 x 108 m s-1
Question: Find the type of radiation of a UV photon with energy as 6.9 × 10-19 Joule?
Solution: As per Planck’s equation the photon’s energy is proportional to its wavelength:
Q = hc/λ
Put the value in the above equation:
6.9 × 10-19 = (6.623 × 10-34 × 2.998 x 108) / λ
λ = 2.88 × 10-7 m = 288 × 10-9 m = 288 nm
λ = 288 nm (this wavelength falls under the region of UVB
How to measure the intensity of light?
For visible light:
1 Lux = 1 lumens/m2
For example, a light source with 100 lumens is spread over 1 m2, which means the illuminance is 100 lux
A high-rated Android smartphone can also measure the illuminance of light in lux directly. Look at this screenshot of a mobile App.
For UV light:
It is not simple to determine the light intensity besides of point source. The irradiation can measure only at the point where the target is located. UV radiometer can be used to measure the irradiation. UVB or UVA light sources irradiation intensity can be measured by the LS125 multi-probe UV lamp intensity meter. Read full article
What are the applications of UV light?
It has immense medical, analytical, and industrial applications. Some area of UV light applications is as below:
- Electronics industry
- Instrumentation and control
- Analytical chemistry
- Biology related research
- Physics-related research
- Photovoltaic cell
- Food engineering
- Photocatalytic reaction
- Sterilization and disinfection
- Air and water purification
- Cancer treatment
- Degradation of recalcitrant