Photometry Radiometry Flashcards
Radiometry:
Power produced by source of EM radiation (Objective)
Photometry:
Effect that the radiation has on the visual system (Subjective)
Luminous power:
total amount of light that emerges in all directions from the source (unit: lumen lm)
Luminous intensity
light power produced in a given direction by a point source (unit Candela (cd)= 1 lumen/steradian)
Luminance
amt of light coming off a surface in a specific direction (Candela/m^2 or nit or apostalib) (e.g. TV)
Illuminance:
luminous power that falls on a surface. (lumens/m^2 or lux) (e.g. Projector screen)
Specular reflector:
reflects all light in one direction (e.g. mirror)
Diffuse reflector:
scatters reflected light in all directions (e.g. matte paint)
Black body:
White body:
absorbs all light
reflects all energy
Bandpass filter:
filter that passes only a certain specified spectral band of light
Narrowband filters:
A filter that passes only a narrow spectral band of light
Broadband filters:
A filter that passes only a broader spectral band of light
Long-pass filters:
filter that transmits long wavelengths of light, but not shorter wavelengths.
Interference filters:
very narrow band of light based on interference principle of light
4 criterions for luminous intensity with diff surfaces:
DIRT Distance from light source Illuminates the surface (how much light) Reflectance of the surface Tilt of the surface relative to your line of sight
100% lambertian surface:
1 lux on gives 1/π nits (0.318) off
1 lux on 1 apostilb off
1 apostilb= 1/π candelas/m^2= 1/π nits
Grey lambertian surface=
reflects 50% of light
1 lux on 0.5 apostilb off
Retinal illuminance=
trolands (Td) is proportional to object luminance and pupil area (not diameter)
Optimal light sensitivity for photopic conditions: ???
Peak luminous efficiency of photopic vision is: ???
Optimal light sensitivity for scotopic conditions: ????
Peak luminous efficiency of scotopic vision is: ????
Optimal light sensitivity for photopic conditions: 555 nm
Peak luminous efficiency of photopic vision is: 680 lu/W
Optimal light sensitivity for scotopic conditions: 507 nm
Peak luminous efficiency of scotopic vision is: 1700 lu/W
UVC:
UV cornea pain, solar keratitis
Luminous efficiency equation
Luminous efficiency= luminous eff680Watts
Inverse square law
E=I/d^2 (E=illumination, I=intensity of point source, d= distance from point source to surface)
Td
Td= (luminance of object in nits) * (pupil area in mm^2)
Area of circle=
Area of circle= πr^2
Eye is more sensitive to what color light?
Green 550 nm
What is the luminous efficiency at 400 nm? given a graph
=0 (get from graph given)* (680/W)* 10W
=0 lumens
What is the luminous efficiency at 600 nm?
= 0.62 (get from graph given)* (680/W)*10W
=4216 lumens
Luminous efficiency:
how many lumens a certain light source produces per Watt
We see better or worse with LEDs at night? what is a disadvantage of LEDs
Better
Disadvantage: 3 times more scattering at 465 nm than at 600 nm
(decreased wavelength increases rayleigh scattering) which causes discomfort glare for presbyopes and cataract pts
RGB cones respond from ________nm with peak response at ____nm.
400-700nm
peak: 555nm
Rods respond from _______nm, with peak sensitivity at _____nm.
400-600nm
peak: 507nm
Peak luminous efficacy of photopic vision is _______ at peak response of _____nm.
680 lu/W
555nm
Peak luminous efficacy of Scotopic vision is __________ at peak response of _____nm
1700 lu/W
507nm
A _____________ filter transmits all wavelengths equally, and minimizes color distortion.
Neutral density (ND)
Optical density equation
OD= log(1/T)
or
OD=log10(1/T)
TP A source of which of the following color temperatures will appear most red? A. 2000K B. 3000K C. 5000K D. 10000K
A. 2000K
TP
The color temp of an incandescent bulb is 3300K. This means that:
The bulb’s spectral distribution matches that of a blackbody radiator whose temp is 3300 K.
TP
A ND filter transmits 50% of 450nm light that is incident upon it. If 40 W of 550 nm are incident on the filter, how many watts are transmitted?
20 W
TP
Which of the following light sources has more energy concentrated in the blue region of the spectrum?
LEDs
TP
A stimulus consisting of 10W (power) of 400nm produces zero lumens of light, whereas a 10-W stimulus of 600nm produces 4216 lumens.
Radiometrically Equal and Photometrically Unequal
TP
One candela is equal to:
1 lumen/ m^2
TP
Appropriate units for luminous power, illuminance, and luminance are:
Lumens, candelas/m^2, lumens/m^2
TP
You are asked to determine if the lighting conditions in the classroom are adequate. The lighting conditions are specified in which units?
Candelas/m^2
TP
When measured at an angle of 10 degrees to its surface a matte surface has a luminance of 50 foot lamberts. What is the luminance when measured 20 degrees from the surface?
50 foot-lamberts
TP:
As a surface is moved away from a light source, the illumination of the surface:
Decreases
TP
As the object in view moves farther from the eye, the retinal illuminance:
Remains constant
