Ultra Violet
June 8th, 2008
Question: Can you see the radiation from an object whose peak blackbody emission lies in the Ultra-Violet band?
How would you solve this?
Can you see the radiation from an object whose peak blackbody emission lies in the Ultra-Violet band? Why or Why not?
Yes, because it is still emitting some radiation in the visible band, though less than at UV
No, because you cannot see UV radiation
Yes, because it is emitting radiation equally at all wavelengths
No, because it is not emitting any visible radiation
Yes, because your eye is sensitive to UV radiationAnswer: Yes
All bodies that are "hot" (meaning: temperature not at Absolute zero) will emit some energy at ALL wavelengths.
What changes is the distribution of this energy among wavelengths (the amount of energy in each bandwidth, for example) and the wavelength of the peak.
Of course, the cooler the body, the less total energy is emitted, so the amount in the visible portion is even less, until there is simply not enough for our eyes to see (but it is still there).
Our Sun peaks in visible light (that is why we have evolved to see better at what we call the "visible" wavelengths).
Stars that are hotter than our Sun will emit far more energy than our Sun, at all wavelengths. And the peak will be at shorter wavelengths (in the ultraviolet, if the star is that hot).
So, a star that is hotter than our Sun will, in fact, emit MORE visible light than our Sun (and a LOT more in ultraviolet, which we can't see)
---
Let's imagine that we could separate the spectrum of energy into very large bands. This is done, in reality, with very narrow bandwidths but we will do it with very large bandwidths.
We will compare the energy emitted by our Sun (6000 K) and by a star with a temperature of (10,000 K)
Each column will show a number that is made up to be simple and without units (I don't want to get into things like watts per nanometres, so I'll just use crude numbers)
And to make everything easier, I will set the intensity at 1 for the Sun in visible light. (The real distribution is more complicated that this and my numbers are not precise).
Sun star band
0.8 :: 2.0 radio
0.9 :: 3.0 infrared
1.0 :: 4.0 visible
0.8 :: 5.0 ultraviolet
0.2 :: 1.0 X-ray
0.1 :: 0.3 gammaAlthough the peak of the other star is in ultraviolet (it emits more energy in ultraviolet than in visible), it still emits more visible light than our Sun.
So, if we were to put both of them at the same distance from our eyes, the other star would appear brighter than the Sun, even if its peak is not visible to our eyes.
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51 UV LED Scorpion Detector Hunter Finder Ultra Violet Blacklight Flashlight AA $9.99 |
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Hugo (DVD, 2012, Includes Digital Copy; UltraViolet) $8.75 |
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New 15 LED+UV+LASER Ultraviolet Flashlight Light Torch $0.01 |
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What is UV Light?
UV or ultraviolet light is a non-visible spectrum of light that surrounds us. Because the increased incidence in skin cancer, we know about the harmful effects of UV radiation on our skin, but we think that UV can also damage the eyes?
UV is composed of three wavelengths of light
UVA closest to visible light, range from 320 to 400 nanometers
UVB - 280 - 320 nm
UVC - 280 - 200 nm
UV could damage my eyes?
UVA and UVB can cause significant damage inside the lens of the eye and retina. It is also harmful to the cornea - The clear window on the front of the eye.
UVA is the most dangerous, especially if you are exposed to low doses over a long period. It can damage the eye, but it is absorbed by the lens. This protects the retina, but as the affects accumulate pigments are generated within the lens, and aging and cataracts develop new exhibition. When cataracts are carried out this vital filter to protect the retina left.
UVB causes sunburn and snow blindness, which is exacerbated by reflection from water and snow. The cornea absorbs its power to protect the internal structures of the eye, but which leaves the cornea vulnerable to problems. Pterygium is a patch of tissue disorder develops on the cornea as a result.
UVC is filtered by the ozone layer, but if you're in an area where the ozone layer is thin, then it may still be dangerous.
Do I need UV protection?
Yes, if one of the following apply:
You spend time on the water.
You had cataract.
You spend more time outdoors.
You like to wear dark glasses.
You're regularly exposed to UV light.
You live where the layer Ozone is thin.
What Will Protect My Eyes?
Wearing spectacles, either dark or light you give some protection against UV, but only total protection from UV filter glass or polycarbonate. Other lens materials provide varying degrees UV protection.
Standard plastic - as these lenses can yellow over time, manufacturers add a small amount of UV filter on the material. They give about 92% UV protection.
Glass - As do not absorb UV they provide no protection.
Lenses that darken in the sun - these are dark lens due to UV light, so they change their block all UV.
UV Filter - This is a glass coating that guarantees to give 100% protection against all types of UV rays.
Sunglasses are sometimes regarded as providing protection against UVA, UVB and UVC. The problem with the list of these categories is that we see the symbol UV and assume we are protected. You must ensure that the lenses filter question all types of radiation.
Do I need a UV filter sunglasses?
Our eyes respond to light live in reducing the size of the pupil. This stops light from going to the retina and lens. So, a stained glass will flood light in the eye, and without a UV filter, internal structures are fully exposed to the dangers of UV.
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