Physical Optics Final: Photometry

What do both photometry and radiometry measure?

electromagnetic radiation

What is radiometry?

measurement of radiant energy in terms of absolute power

What is photometry?

measurement of light in terms of its perceived brightness to the human eye

What does radiometry care about?

the source

What is energy in photometry?

luminous energy (talbots)

What is energy in radiometry?

radiant energy (Joules)

What is power/flux is photometry?

luminous flux (lumens)

What is power/flux is radiometry?

radiant flux (joules/sec=watt)

What part of the electromagnetic spectrum is referred to as light?

visible part

What is photopic vision?

daylight vision

What is the relative luminous efficiency curve (Vλ)?

relative luminous efficiency across EM spectrum with daytime/photopic vision

What is the range of relative luminous efficiency (Vλ)?

Vλ=0-1

When is Vλ=1?

@555nm (max sensitivity)

When is Vλ almost 0 (<0.001)

@380nm + 760nm (min sensitivity)

Absolute luminous efficiency curve ranges from? (Kλ) ?

0-683 lumens/watt

what is maximum absolute luminous efficiency (Kmax)? Where is this at?

683 lumens/watt

@555nm

What is intensity for a point source in photometry?

luminous intensity (I) in lumens/steradians aka candela

What is a candela?

lumens/steradians

What is intensity for a point source in radiometry?

radiant intensity (Ie) in watts/steradian

How do you solve for luminous intensity of a point source?

1. energy per quantum

2. radiant flux

3. radiant intensity

4. luminous intensity

What is intensity (per area) for an extended source in photometry?

luminance (L) in candela/area

What is intensity (per area) for an extended source in radiometry?

radiance in watt/steradian/area

How do you solve for luminance of an extended source?

1. energy per quantum

2. radiant flux

3. radiant intensity

4. luminous intensity

5. luminance

What is flux onto a receiving surface in radiometry?

irradiance (watts/area)

What is flux onto a receiving surface in photometry?

Illuminance (E) in lumen/area

When is illuminance (E)=I/d^2?

for a point source with no tilted receiving surface

for a circular extended source whose receiving surface is on axis of source

How do you calculate illuminance/irradiance for point source?

1. energy per quantum

2. radiant flux

3. radiant intensity

4. luminous intensity

5. illuminance/irradiance

How do you calculate illuminance/irradiance for an extended source?

1. energy per quantum

2. radiant flux

3. radiant intensity

4. luminous intensity

5. illuminance/irradiance

What is s in Eret=L x s?

pupil area (πr^2)

when does retinal illuminance increase?

when pupil size/area increases

What is the units of retinal illumination?

trolands

What is L in retinal illuminance equation? (Eret= L x s)

L= luminance of target

What is the set up for Maxwellian view?

light source directed into center of pupil, with no light on iris

What are the two major characteristics of Maxwellian view?

1. bypass pupil: pupil fluctuations do not influence retinal illumination

2. generates very high levels of light on retina

What does Stiles-Crawford 1 say?

light rays traveling through the periphery of the pupil are less effective in stimulating vision than rays passing centrally thru pupil

What is Stiles-crawford 1 effect dependent on?

wavelength

When is stiles-crawford 1 effect the largest? smallest?

largest at 400 nm

smallest at ~560nm

What is the Stiles-Crawford II effect?

monochromatic rays passing through periphery of pupil would have the appearance of its natural wavelength + amount shown on Y axis when passes through the center of the pupil

What λ does Stiles Crawford II have no color change points?

~500nm + ~555nm

What is incandescence?

production of light through thermal excitation (heat) of a liquid, solid, or gas

What is luminescence?

production of light in any other way that incandescence

What does spectrum distribution of incandescence light depend on?

temperature and substance

What is Kirchoff's Law?

Absorbance = Emissivity

What is emissivity?

% of emitted radiation

What does the Stefan-Boltzmann Law tell us?

total output of blackbody at a certain temperature

What relationship does Wien's displacement law describe?

relationship between temperature and color

What happens to incandescent light as it burns hotter according to Wiens law? (2 things)

it becomes bluer

and

it becomes more efficient

What is the distribution temperature?

absolute temp of a blackbody whose relative spectral distribution is the same in the visible region as the light source

What is color temperature?

absolute temp @ which a blackbody must be operated in to have the same chromaticity of the object in question

What does distribution temp and color temp apply to?

incandescent light

What is the efficiency of a typical incandescent bulb?

10-25 lumens/watt

What is the most efficient incandescent source What is its efficiency?

the sun

85 lumens/watt (not very efficient)

When will you get maximum efficiency of an incandescence source? What would that be?

if all energy is given off at 555nm

683 lumens/watt

is incandescent light efficient?

no

What is electrical discharge?

electrical conduction through a gas in an applied electrical field

What is higher efficiency, incandescent light or luminescence light?

luminescence

What is the efficiency of a low pressure mercury light?

35-65 lumens/watt

If a light is inefficient what does that mean?

a lot of energy is being released as UV/infrared, instead of visible spectrum

What kind of spectrum does a low pressure mercury light emit?

line spectrum

What is an example of a fluorescent source?

low pressure mercury lamp + phosphor

What is the efficiency of low pressure mercury lamp + phosphor (fluorescent source)?

80 lumens/watt

more efficient

Why is low pressure mercury lamp + phosphor (fluorescent source) more efficient?

they absorb UV light to create more visual light

What kind of spectrum does low pressure mercury lamp + phosphor emit (fluorescent source)?

wide spectrum

What is the efficiency of a high pressure mercury lamp?

100 lumens/watt

What is high pressure mercury lamps good for?

color

What is the most efficient light? What is its efficiency?

low pressure sodium light (140lumens/watt)

What is the disadvantage to low pressure sodium light?

not good for color, emits almost pure monochromatic light (589nm)

What is the efficiency of high pressure sodium light?

120 lumens/watt

What spectrum does high pressure sodium light emit?

wide containing most colors

What is phosphorescence?

similar to fluorescence but there is a time delay between absorption and emission

What must be true to get a fluorescence?

wavelength of emitted radiation must always be longer than the wavelength of incident radiation

What does the emitted spectrum of fluorescent source depend on?

type of phosphor coating NOT the wavelength of incident light

What is the time delay of phosphorescence due to?

metastable state where atom stays for a considerable time before dropping to lower state

What does the time delay allow phosphorescent source to do?

continue to radiate light after source is removed

What is stimulated emission of radiation used for?

to amplify a light beam (makes laser)

What is the second photon like in stimulated emission of radiation?

second photon is identical to original photon

What is true in a laser?

stimulated emission > photon absorption

What do you need to get stimulated emission/laser? how do you get this?

need atoms in excited state

via pumping medium with energy

Why is light released from stimulated emission highly monochromatic?

photons released are identical

What three things are necessary for the production of __________ light?

1. population inversion

2. spontaneous emission

3. stimulated emission

What is population inversion?

More electrons in the excited state(s) that the ground state

What are the 3 advantages of a laser?

1. collimated (parallel) beam

2. high intensity when focused

3. very monochromatic with long coherence length

What is a photodetector/photoelectric?

changes electrical properties of metals due to photoelectric effect

What is inner photoelectric effect (photovoltaic)?

electrons move from low energy to high energy

converts light into electrical energy

What photoelectric effect is used to make solar cells?

inner photoelectric effect

What is the outer photoelectric effect (LED)?

electron moves from high to low energy state

creates light using electrical energy

What light do LEDS (light emitting diode) emit?

monochromatic light

How do LEDs produce white light?

1. combining 3 different wavelengths

2. through fluorescence

What are the advantages to LEDs?

instantaneous on/off

long life

increased efficiency

low temp

What kind of wavelengths pass through interference filter and what light does it produce?

multiple wavelengths pass through

produces nearly monochromatic light

What does destructive interference of interference filter create?

no reflection and strong transmission

What does constructive interference of interference filter create?

strong reflection and no transmission

What does the total of reflected, absorbed, and transmitted light of a filter equal to?

200%

What is transmittance?

transmitted light/incident light

What does it mean that neutral density filters are non-selective?

transmission is same for all wavelengths

What things are neutral density filters?

carbon in glass

polaroids

episcotister

What is an episcotister?

sectored disc

What is an episcotister used for clincally?

RAPD

Pulfrich effect

What type of filters are color temp changing filters?

selective

What does mired mean?

micro reciprocal degree