UV Light in Tanning - Sunburn is a result of too much exposure to dangerous UV light. The body’s natural defence mechanism kicks in and produces a pigment called melanin. The body sends this pigment into neighbouring cells to try and prevent damage. Tanning beds use UV lights that pass electric currents through vaporised mercury to create the sun's rays.

Electromagnetic waves work differently. All waves of the same type of frequency travel at the same speed. But their wavelength and frequency differ, depending on the type of wave. The frequency of a wave is measured in Hertz; its unit is Hz.

Light travels in waves, but unlike waves on the ocean, they are much too small for us to see with the naked eye. A polarizer is a light filter that only allows light waves that are moving in one direction to pass through, letting us indirectly observe some of the wave properties of light. This aligned light that passed through a polarizer is called polarized light.

Ultraviolet light wavelength rangechart

Lamps - Lots of substances can absorb UV light. Some naturally occurring substances like plants and fungi and some man-made substances like synthetic fluorophores will do it too - one of them being fluorescent lamps. When UV light is absorbed, electrons in the material reach a higher energy level before gradually returning to their original position. Each time they do so, they release a small amount of the energy they have absorbed as visible light.

uv-visiblerangein nm

Ans: Ultraviolet radiation is electromagnetic radiation with a spectrum that ranges from violet to a frequency we can't see. UV radiation is imperceivable to the human eye, but it can cause certain materials to fluoresce when it falls on them. Insects like bees, who can see UV radiation, can be attracted to fluorescent lights. UV radiation is a form of energy that is created in a continuous spectrum in the Sun and in a discrete spectrum in a vacuum tube. 99% of UV radiation reaches Earth’s surface in the form of UVA rays. Out of that, 99% reaches Earth’s surface in the form of UVA rays.

Ultraviolet rays are in the wavelength range from 10 to 400 nanometers (nm). They come in the frequency range of 800 terahertz (THz) to 30 petahertz (PHz). Ultraviolet radiation is usually divided into four regions.

5 uses ofultravioletrays

If you have a cell phone camera, you can place the filter in front of the camera and try this yourself. Take pictures of the same scene while rotating the filter and see if you notice a color and contrast change. Important hint: there is an angle where light is strongly polarized, called the Brewster's angle, and if you are at this angle the effect will be very easily noticeable as in the 2 photos below. This angle depends on the surface among other things, but about 53 degrees will be close.

When you look up at the sky with a polarizer, there is something even more subtle happening. Observe how deep the color of the sky is while you rotate the polarizer. You will likely notice a change in brightness and color of the sky, and you may notice that clouds are more visible at times. This is because the sunlight passes through our atmosphere and reflects off air molecules, and also becomes slightly polarized. This will vary quite a bit by time of day, mostly due to the angle of the sun. Photographers have been using polarizers like this for decades to create vivid outdoor pictures.

Now rotate your polarizer and watch some objects like cars, windows, or other shiny objects. You should notice that some of the reflections disappear. While sunlight is randomly polarized, once it reflects off a surface, it tends to become polarized because of how the light waves interact with the surface. This will depend on the type of surface and angle of reflection, and can be very complicated. However, we can still see the effects of these nearly invisible waves through the polarizer.

Some are polarized, but not all. It depends on the light source and how the optics are designed. With your polarizer filter, you can test this. If you have a laser pointer, shine the light through the polarizer and rotate it. Observe the laser spot on a piece of white paper (in a darkened room will work best). Does the brightness of the spot change when you rotate the polarizer? If it does, your laser is partially polarized. If the laser spot almost disappears, it is mostly polarized.  We can say 'partially', 'almost', and 'mostly' because perfectly polarized light is difficult to create - it requires a very good light source, very good optics, and a vacuum because even air molecules can scatter light and create polarization.

what protects humans from harmful uv-b rays

Ultraviolet lightfrequency

Photography - UV photography is a specialised type of photography that allows photographers to capture images with UV light. Most UV photography is used for medical, scientific and forensic purposes. Nature photographers may take pictures of flowers with UV photography because the human eye can’t see these details. By using UV photography, they can capture only the UV light that hits the camera sensor.

One major difference between UV and visible light is its wavelength; UV has a smaller wavelength than visible light. The electromagnetic spectrum is divided into different “bands” depending on wavelength - ultraviolet light is the shortest, while infrared light is the longest. The term “visible light” refers to the part of the spectrum that the human eye can see.

Extinction ratio probably reminds you of Jurassic Park, however, it is also an optical term and it means almost the same thing. Extinction of light measures how much light is eliminated. For example, atmospheric extinction which means the amount of light blocked by the atmosphere. In our case we are causing extinction by filtering.

UV light wavelengths are measured in nanometres, with one nanometre equal to one billionth of a metre. Ultraviolet rays are shorter wavelengths than visible light, which is why we cannot see them when seen naked-eye.

If you align the polarizers so the maximum light goes through, then slowly rotate one by 90 degrees and it will go from maximum to minimum. The ratio of the maximum to minimum is called the extinction ratio.

Ultraviolet light wavelength rangein meters

Ultraviolet light wavelength rangein nm

Ultraviolet light has many uses, including treating skin diseases like lupus and vitiligo, but photography is one of its most common uses. The same technology that produces blacklight posters, fluorescence art, sunless tanning solutions, and teeth whitening products also provides us with protection from pests like bed bugs. Here are some of UV light uses in detail:

Take two polarizers and place one on top of the other, and then rotate one of them. You’ll notice they go from light to almost completely dark. What is happening? When the two polarizers are aligned, they let light through, but when they are misaligned by 90 degrees, they will block almost all light. The first polarizer is only allowing waves in one direction to pass, and they are then blocked by the second polarizer which only let waves pass aligned to the opposite direction.

Ultraviolet (UV) light is a type of electromagnetic radiation on the electromagnetic spectrum. The frequency of UV light is higher than that of visible light. This means it has more energy, which makes its wavelength shorter. This increased energy causes chemical effects in many objects — such as skin, plastics, and even some clothing dyes.

A majority of the UV rays that humans come in contact with the sun. However, other UV light sources also exist. Black lights, mercury lamps, and tanning lights all emit at levels of UV radiation.

1. What makes filters with higher extinction ratios? Is a perfect filter possible, for example infinity:1 extinction ratio?

First let's calculate the extinction ratio. For the data collected above it would be 17,300/20 or 865:1. We can also calculate the % transmission of just a single filter, which would be 4,000/17,300 23%. Here is a table with these two calculated values:

With your PocketLab or with a light meter, you can use sunlight or a bright lamp as a light source. Both of these sources are unpolarized light. You will measure the light from the lamp directly with no filter, with one filter, with both filters, and again with both filters but rotated 90 degrees. Record these four measurements. If you're using your PocketLab, the reading will be in lux, which is the SI unit of illuminance, equal to one lumen per square meter. The graph below was generated by a PocketLab Voyager, and you can clearly see four different light levels, and the recorded values are in the table below:

When you rotated the two polarizers, did you notice that they went from light to dark continuously? We should then be able to create any lux value between our readings in the first table; 3,300 lux with two aligned filters down to 20 lux with two crossed filters.

Direct sunlight is unpolarized, meaning that the waves travel in many random directions. When sunlight passes through a polarizer, only the waves that are aligned in the direction of the polarizer filter are able to pass through. Hold up your polarizer filter to the sky. You’ll notice that a polarizer filter looks dark, and that is because it is only letting through the aligned light waves.

1. UVC rays do not reach the earth’s surface as most of them are absorbed by the atmospheric nitrogen, oxygen, and ozone, and the rest are scattered.

Ultraviolet lightexamples

Cancer Treatment - One of the benefits of UVA light is that it can be used to treat skin cancer. Psoralens, or drugs, are given to patients to react to the UVA light and slow the growth of cells on the body. Patients who use this treatment experience great benefits, such as having treatments with lamps similar to tanning beds. There is some risk of burning the skin if not careful, but proper calibration will minimise this risk.

Specification sheets for polarizer filters from an optics catalog (for example Edmund's Optics) show a range of transmission from 20% to 42%, and an extinction ratio from 19:1 to 10,000:1. Our data is within that range.

2. Most of the filters in the optics catalog are around 20%-40% transmission, and in general the more expensive filters have lower transmission. Is there a model you can draw of what may be happening to the light waves?

Chemistry - UV lights are used by scientists to examine the chemical structure of a compound. The sensitive machine, called a spectrophotometer, monitors colour changes in UV light radiation to determine how much of a certain compound is present. This process is often used in a variety of industries. For example, it can identify unwanted compounds in water by monitoring a change in colour during drinking water production.

Ans: Ultraviolet light waves are those waves that occur at the lower end of the UV spectrum, with a range of 400 to 10 nanometers. Ultraviolet waves are below the visible light spectrum, and these waves penetrate deeply into the skin and other items. The UV frequency waves range from 7.5x1014 to 3x1016 Hertz. Ultraviolet light is lower than visible light, which ranges from 750 to 400 nanometers. The sun emits UV light in the form of UVA, UVB, and UVC. Ultraviolet B rays have the power to cause sunburns, but the ozone layer absorbs most of them. Although these rays are invisible, they also can be beneficial. For example, UV lamps are useful in medical settings such as surgery rooms, where they destroy germs or microbes on surgical instruments.