1st Class Light Sources2

7/24/2019 1st Class Light Sources2

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PHOTOMETRY LIGHT AND RADIATION SOURCES

The sun is the most important and most familiar source

of light and radiation. The total radiant power of the sunis said9 to be 3.9x 1023 Kw.

While most of this energy is radiated into space, the

irradiance at the earth’s outer atmosphere is between

132 and 140 mWcm-2 .



This irradiance is attenuated by the atmosphere by a

factor of 0.7 to 0.8 on a clear day. As a round figure, 100

mWcm-2 has been proposed as the magnitude of “one

solar constant” and termed One sun.



THE EFFICACY OF LIGHT AND RADIATION

There are two ways of defining the efficacy of

a light source.

If a monochromatic source is considered it

would be compared with a source of

wavelenght 555 nm of 673 lm/W.

If, on the other hand, a white light source



It would be compared with an equal-energy

hypothetical source concentrated within the

visible spectrum with maximum efficacy of

about 187 lm/watt

The maximum luminous efficacy of white light

depends on the wavelength interval

considered visible.



LUMINOUS EFFICIENCY

The luminous efficiency of this source must be

187/673 = 27.8% máx.

In this case the amounts 187 and 673 lm/W

means both are radiated



The efficacy of the fluorescent lamps or sources

does not include the energy disipated in the

electronics.

It depends of the color





One light source with a luminous efficacy of

115 lm/W

Compared with a maximum value for sources of

continuous spectre of 187 lm/W

It will be 115/187 = 61.5 % efficiency.





The Illuminance of natural sources

The daylight is composed by the sun light plus

the skylight, both increase as the sun rise in the

sky.

The maximum Illuminance due to skylight is16,000 lx

The maximum Illuminance due to sunlight is

102,000 lx.

The maximum Illuminance due to both are

118,000 lx



BLACK BODY RADIATION

The blackbody radiation is a hipotetical

source of radiant energy which is used as a

standard in order to compare other sources.

The blackbody is a radiator who radiation depends only of the temperature, it radiates

more energy to some temperature that

anybody at the same temperature.

It absorbes all the incidente optical radiation

without radiates any.



COLOR TEMPERATURE

The color temperature of a source of light isthe temperature (kelvins) of a blacbody that

would radiate light of the same chromaticity.

e s r u on empera ure o a g source

is the temperature of a blackbody thet would

radiate light of the same spectral energy

distribution



The term color temperature is often used

when the context implies the distributiontemperature, a light source non thermal can

have a temperature different of his color

.

Examples: A fluorescent source and a thermal

source masked with a filter, can be matched

the color temperature but the fisical

temperature are different



The white mantle of a gas or gasoline lamp

was probably the first incandescent lamp, butthey are rarely used now because the electric

lamp is more efficient, easier to control, safier,

and provides more light for less money

easily switched. It is remarkably constant and

repeatable in performance if not operated at

too high a temperature.

The fused point is about 3650 K and it can be

operated at high temperature in vacuum and

in an inert gas.



The white mantle of a gas or gasoline lamp

was probably the first incandescent lamp, butthey are rarely used now because the electric

lamp is more efficient, easier to control, safier,

and provides more light for less money

easily switched. It is remarkably constant and

repeatable in performance if not operated at

too high a temperature.

The fused point is about 3650 K and it can be

operated at high temperature in vacuum and

in an inert gas.



This process produces energy as heat and

light , the latter being 5% of the total energy

consumed . Usually have a double coiled

in an atmosphere without oxygen : Ar , N.



1.Incandescent inert atmosphere (common)are distinguished because they emit a

pleasant, warm light.

2.No need for auxiliary equipment on andrestart , this being instantaneous.



1.On the market a variety of shapes, sizes ,wattages and colors; with and without

built-in reflector.

2.Intensity is proportional to the area of thefilament.

.temperature as power is dissipated in thecold bulb





Its operating position is universal and are

provided with screw caps or bayonet

Fallas, by thinning the filament or vibration is so

placed support wires . The base is contact and

support.

The light emission gradually decreases in the

course of its life , since the filament is partially

evaporated , thereby reducing its sectionincreases resistance and also produces a

blackening of the bulb



3) A halogen lamp, also known as a tungsten

halogen, quartz-halogen or quartz iodine lamp,

is an incandescent lamp that has a small amount

of ahalogen such as iodine or bromine added.

The combination of the halogen gas and

the tungsten filament produces a halogen

cycle chemical reaction which redeposits

evaporated tungsten back onto the filament,

increasing its life and maintaining the clarity of the







Gas discharge lamps are a family of

artificial light sources (or lamps). These

lamps produce light by

sending electricity through a ionized gas.Most of these lamps use a noble gas, or a

combination of noble gases, but they often

contain other materials, such

as mercury, sodium or metalhalides.





The gases in these lamps are ionized in

operation. This means that there arefree electrons.

When a electric current is sent through the

gas, e ec rons co e w a oms o e

gas and the metals. This will mean that

some reach a higher energy state. When

they fall back into the lower energy state,

they will emit the energy in the form







Ultraviolet (UV) light is an electromagneticradiation with awavelength from 400 nm to

100 nm, shorter than that of visiblelight but longer than X-rays.

Though usually invisible, under some

conditions children and young adults cansee ultraviolet down to wavelengths ofabout 310 nm, and people with

aphakia (missing lens) can also see someUV wavelengths.

Near-UV is visible to some insects

and birds.





An LED lamp is a light-emitting diode (LED)

product that is assembled intoa lamp (or light bulb) for use in lighting

fixtures.

amps ave a espan an e ec r ca

efficiency that is several times better

than incandescent lamps, and significantly

better than most fluorescent lamps, with

some chips able to emit more than 100







LEDs emit light in a very narrow band of

wavelengths, emitting light of a colorcharacteristic of the energy bandgap of

the semiconductor material used to make the

.

either mixing light from red, green, and blue

LEDs, or using a phosphor to convert some of

the light to other colors.



One method (RGB or trichromatic white LEDs)

uses multiple LED chips, each emitting adifferent wavelength, in close proximity to

generate white light. This allows the intensity of

color.



The second method uses LEDs in conjunction

with a phosphor. The CRI (color renderingindex) value can range from less than 70 to

over 90, and color temperatures in the range of

7000 K are available





A laser is a device that emits light through a

process of optical amplification based onthe stimulated emission of electromagnetic

radiation

A laser differs from other sources of light in that it

emits light coherently . Spatial coherence allows

a laser to be focused to a tight spot, enabling

applications such as laser

cutting and lithography.





Spatial coherence also allows a laser beam to

stay narrow over great distances (collimation),enabling applications such as laser pointers.

Lasers can also have high temporal coherence,

narrow spectrum, i.e., they can emit a single

color of light.

Temporal coherence can be used to

produce pulses of light as short as a







A laser diode, or LD, is an electrically

pumped semiconductor laser in which the activelaser medium is formed by a p-n junction of

asemiconductor diode similar to that found in

- .



The laser diode is the most common type of laser

produced with a wide range of uses thatinclude fiber optic communications, barcode

readers, laser pointers, CD/DVD/Blu-ray

, ,

scanning and increasingly directional lighting

sources.









Gaussian beam is a beam of

monochromatic electromagnetic

radiation whose transverse magnetic

and electric field amplitude profiles are given

by the

Gaussian function this also im lies a

Gaussian intensity (irradiance) profile.

This fundamental (or TEM00 )

, transverse gaussian mode describes the

intended output of most (but not all) lasers



The mathematical expression for the electric field

amplitude is a solution to the paraxial Helmholtz

equation. Assuming polarization in the x direction and

propagation in the +z direction, the electric field

in phasor (complex) notation is given by:

where



f(x) = ae(x-b)2

E (r,z) =E0 {W0/W(z)} exp [-r 2/W2(z)][exp (-

i(kz+k[r 2/2R(z)] -(z))

.



Beam width or waist, Ancho del haz o tamaño del

punto

El haz Gausiano de ancho w (z ) esta dado como función de la

distancia axial z . La cintura o ancho mínimo del haz es w :



Gaussian beam width w (z ) as a function of the axial

distance z . w 0: beam waist; b: depth of focus; z R:Rayleigh range; Θ: total angular spread

For a Gaussian beam propagating in free space, the

spot size w (z ) will be at a minimum value w 0 at one

place along the beam axis, known as the beam waist .

For a beam of wavelength λ at a distance z along the

beam from the beam waist, the variation of the spot size

is given by



where the origin of the z-axis is defined, without

loss of generality, to coincide with the beam

waist, and where

is called the Rayleigh range.

Rayleigh range and confocal parameter a s ance rom e wa s equa o e ay e g

range z R, the width w of the beam is

The distance between these two points is calledthe confocal parameter or depth of focus of the

beam:

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1st Class Light Sources2