Photometry (conceptual)

what is the difference between photometry & radiometry?

photo - includes human sensitivity

radio doesn't

a relative luminous efficiency (Vλ) ranges from Vλ = ____ to Vλ = ____

0-1

relative luminous efficiency (Vλ)

Vλ = 1 when λ=____

555nm

(max luminous)

relative luminous efficiency (Vλ)

Vλ = 0 when λ = ____

380nm or 760nm

(min luminous)

the maximum absolute luminous efficiency (Kλ) for humans is...

683 lumens/watts

wavelength of 555 nm corresponds to Vλ = _____ and Kλ = ____

Vλ = 1

Kλ = 683 lumens/watt

radiant energy is measured in... (what units?)

joules

luminous energy is measured in... (what units?)

talbots

radiant flux is measured in... (what units?)

Watts

or Joules/sec

luminous flux is measured in... (what units?)

lumens

def of power/flux

energy flow

(energy per second)

def of intensity

flux produced at a certain angle

radiant intensity is measured in... (what units?)

watts/steradians

luminous intensity is measured in... (what units?)

lumens/steradians

or candelas

difference between intensity & intensity per area

intensity is used for point sources

intensity per area is used for extended sources

radiant intensity per area is measured in... (what units?)

watts/area

or steradians/area

luminous intensity per area is measured in... (what units?)

lumen/area

or sterandians/area

or candelas/area

what are the basic 5 steps that can be used to solve problems with primary light sources?

1. solve for Eλ

2. solve radiant flux

3. solve for Ieλ

4. solve for Iλ

5. solve for luminance or illuminance

irradiance is measured in... (what units?)

watts/area

illuminance is measured in... (what units?)

lumen/area

what is the difference between primary & secondary light sources?

primary - the source of light produces its own light

secondary - the source of light is a reflection off of a surface

circular light sources are __(point/extended)__ sources

extended

secondary (or "reflected") light sources are considered __(point/extended)___ sources

extended

the sin^2 law is only used for _____ light sources

circular

def of retinal illumination

amount of light falling on retinal

what units in Eret in? (retinal illumination)

trolands

advantages of Maxwellian view

bypass pupil, high levels of light on retina

Eret NOT affected by pupil size

what is Stiles-Crawford Effect type 1?

BRIGHTNESS difference between central & peripheral retina

center - brighter

peripheral - dimmer

** wavelength-dependent

what is Stiles-Crawford Effect type 2?

COLOR difference between central & peripheral retina

periphery shifts to shorter wavelengths (more blue)

what is the difference between incandescence & luminescence light sources?

incandescence - light from thermal excitation of solid, liquid, gas

luminescence - light of electric discharge from the gas

Planck's Law (for incandescent light sources)

describes output spectrum

will change with temperature & substance type

* works for black bodies *

Kirchoff's Law (for incandescent light sources)

emissivity = absorbance

Stefan-Boltzmann Law (for incandescent light sources)

* works for black bodies *

that's all I know

Wien's displacement (for incandescent light sources)

hotter source = BLUER light (shorter wavelength) & more efficient

the output from an incandescence light source can be described using ___ temperature & ____ temperature

distribution temperature & color temperature

efficiency of a typical incandescent bulb

10-25 lumens/watt

max efficiency of an incandescent light source

683 lumens/watt

efficiency of the sun (an incandescent source)

85 lumens/watt

efficiency of a low pressure mercury lamp

35-65 lumens/watt

WITH FLUORESCENCE: 80 lumens/watt

t or f: the spectrum from a low pressure mercry lamp is continuous

false

which has a better efficiency: incandescent or luminescence light sources?

luminescence

efficiency of a high pressure mercury lamp

100 lumens/watt

t or f: mercury lamps emit a wide spectrum

true

efficiency of a low pressure sodium lamp

140 lumens/watt

t or f: low pressure sodium lamps emit a wide spectrum

false, they release monochromatic light

efficiency of a high pressure sodium lamp

120 lumen/watt

t or f: high pressure sodium lamps emit a wide spectrum

true, they emit multiple colors

the lowest energy state of a photon is called...

ground state (E0)

how do you solve for the absorbed/emitted energy of a photon?

E1 - E0 = hc/λ

to create fluorescence, the emitted λ needs to be __(longer/shorter)__ than the absorbed λ

λemit > λabsorb

what is the difference between fluorescence & phosphorescence?

phosphorescence is stable for a longer time ("time delay")

t or f: lasers emit a wide spectum

false, they emit monochromatic light

steps to create a laser beam

1. pump e- to excited state

2. e- naturally falls to metastable state

3. when e- falls to ground state, it emits a photon, which starts a cascade

t or f: lasers are an example of photoelectic effect

false, lasters use phosphorescence

def of photoelectric effect

occurs in metals

outer vs inner photoelectic effect

outer: e- kick out of metal

inner: e- move around in the metal

t or f: LEDs emit a wide spectrum

false, they emit monochromatic light even though it is white

t or f: LEDs are an example of fluorescence

true

advantages of LEDs

instant on/off

long life

high efficiency

low temperature

what is an interference filter? what kind of light leaves the filter?

filters light so that only wavelengths of the same harmonic passes through

"monochromatic" light - only one wavelength is in the visible spectum

4 ways to make a neutral density filter

thin plastic filter

carbon in glass

polaroids (Law of Malus)

episcotister (sectored disk)

color temperature changes filters are measure in ____ units

MIRED

humans can see a color change when there is a __#__ MIRED difference

5

examples of cut-off filters

UV coating, blue blockers

what are cut-off filters?

filters out light past a certain wavelength

what is a bandpass filter? what light leaves the filter?

narrow range of wavelengths can pass through

(i.e. will only permit blue light to pass)