Lecture
Radiation
State visible range of light
State range of light human eyes respond too and
define UV radiation and IR radiation
More than 80% of info is through light
Use optimum resources at economic prices.
Need electrical power system
Need AC in nature
Light is that radiant Energy
that provides visual sensation for eyes
It is akin to radiant hears but with different wavelengths and freuquencies
visible light spans 180nm
Nanometres
to 500 nm
Human eye
So you can see 700nm red
Can see violet colour 200nm
red to violet 700 - 380 nm
Relative Energy
Visible spectrum 380 nm 800nm
500 - 600 nanometres is in the green yellow region.
Ultra violet is light below 300 nm
300 metres per micro second.
Ultra Violet
ultra Violet - Visual spectrum - Infra Red
Infra red lamps can be used to hear rooms.
can be used for drying heating, and lightening photos.
UV is used for germicidal applications.
Relative luminosity
Ability of eye to respond
400nm is quite low repsonse form human eye
The MAX response of human eye is to green yellow zone.
Artificial sources
Incandescent lamps are some of the foremost uses of artificial light,.
Gas discharge lights. Discontinuous lights. They radiate light at specific frequencies.
Spectral energy
relative energy, luminosity Nanometres
The sun is more our less through the spectrum.
The blue sky peaks art 440
The eye responds most to 550 nanometres. This means the blue sky peaks at 440 nm but the eye is less bale to respond so the energy is of no use.
Incandescent bodies give out radiation that is maintained at higher temperatures.
Yet you do not want evaporation of filament material.
Physical processes that enable us to have artificial sources
Incandescence. Thermo luminescene depends on radiation temperature
Incandescent lamp
Gas Lamps
Candles
Oil
Luminous output is standardized at candelas.
Continuous spectrum
All modern way is to get similar continuous spectrum
at economic and optimum resources.
Term to remember
electro luminescence produces line spectrum
this is a chemical or electrical action on gas vapour that leads
to light radiation
this produces Colour depends on material employed.
line spectrum not continuous spectrum.
fluorescence lamps is most used source of light next to incandescent
There is photoluminescence.
Radiation is absorbed at one wavelength then radiates another wavelength.
If a material can absorb at one wavelength and radiate another,
then this is fluorescence it absorbs at one wavelength and
radiates in visual spectrum, absorbs UV radiation.
zinc , uranium,
Phosphorescene Energy absorbed at one wavelength then radiates later.
use paints that contain calcium.
Radiation after exposure to light.
Phosphorescene Does not require original source of light once exposed to light it slowly radiates.
fluorescence is right away.
Good lighting uses combination of luminescence and fluorescence.
intensity depends on kind of gas used.
Central is that radiation temperatures an important issue.
Black body is one that
is not transparent does not reflect
but absorbs all energy
Energy radiated is proportional to temperature high temperature higher output,
Sun temp at 550nm.
90 lumens per watt.
for most sources lumens per watt of energy consumed.
for 4000k the spectral max 100nm.
higher temperature high is relative max energy.
6500 - 7000 k 43 % if visible energy
occurrence of max at different levels is called displacement.
Grey Body
Energy radiated at each wavelength is less than that is in the case of black body.
So it reflects a certain % of energy at each wavelength.
Carbon filament lamp is a grey body.
selective raidators they radiate less total energy compared to a black body but does radiate more energy at certain wavelengths.
colour temperature is temperature at which black body must be heated to match colour.
Blue sky 25,000 k
Florescent lamp is 4500 k
500 w day light 5000k
extreme blue sky can be matched 1 daylights fluorescent lamp.
500 watt daylight lamp does not match bright sunlight.
light is radiant energy that provides visual energy.
incandescence - Continuous spectrum Lower efficiency
Luminescence -
fluorescence -
Phosphorescence -
Power loss is inversely proportional to operating voltage.
Luminescence is light that usually occurs at low temperatures, and is thus a form of cold body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions, or stress on a crystal. This distinguishes luminescence from incandescence, which is light generated by high temperatures. Historically, radioactivity was thought of as a form of "radioluminescence", although it is today considered to be separate since it involves more than electromagnetic radiation.
he following are types of luminescence
- Bioluminescence, by a living organism
- Chemoluminescence, resulting of a chemical reaction
- Electrochemiluminescence, by an electrochemical reaction
- Crystalloluminescence, produced during crystallization
- Electroluminescence, in response to an electric current passed through it
- Cathodoluminescence, where beam of electrons impacts on a luminescent material such as a phosphor
- Mechanoluminescence, resulting from any mechanical action on a solid
- Triboluminescence, generated when bonds in a material are broken when that material is scratched, crushed, or rubbed
- Fractoluminescence, generated when bonds in certain crystals are broken by fractures
- Piezoluminescence, produced by the action of pressure on certain solids
- Photoluminescence, absorption of photons causing re-radiation of photons
- Phosphorescence, delayed re-radiation
- Fluorescence, where the emitted photons are of lower energy than those absorbed
- Radioluminescence, produced in a material by the bombardment of ionizing radiation
- Sonoluminescence, from imploding bubbles in a liquid when excited by sound
- Thermoluminescence, when absorbed light is re-emitted on heating.
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