Radiometry/Photometry Flashcards
What are the wavelength ranges for UVA , UVB, UVC? What absorbs each? What is a result of absorption of UVA and UVB?
UVA: 320-400 nm. Absorbed by lens
UVB: 280-320 nm. Absorbed by lens
UVC: 200-280 nm. Absorbed by ozone layer and cornea.
Absorption of UVA and UVB leads to progression of cortical cataracts.
Wavelengths for near, mid, and far Infrared radiation
Near: 800-2500 nm
Mid: 2500- 50,000 nm
Far: 50,000 - 10^6 nm
What size of wavelengths are more dangerous? Shorter wavelengths or longer? Why?
Shorter wavelengths (higher frequency) are more dangerous due to their higher energy.
If a wave has a higher amplitude, it will be _______ than a wave that has a lower amplitude.
Brighter
Wavelength and frequency are ___________ proportional.
Inversely proportional
Formula for frequency of light
v = c / λ
v = frequency of light c = speed of light (3 x 10 m/s) λ= wavelength of light
As the wavelength gets longer, the frequency gets _______.
Smaller
Energy equation
E = hv
E = energy per photon h = Planck’s constant (6.626 x 10 J -sec) v = frequency
OR
E = hc / λ
E = energy per photon h = Planck’s constant (6.626 x 10 J -sec) c = speed of light (3 x 10 m/s) λ = wavelength
As the wavelength gets longer, the energy per photon is ______.
lower
A type of retinal ganglion cell (ipRGC) contains a photopigment called _________. What does it do when it is stimulated?
Melanopsin. When stimulated by sunlight, the cell sends information to the suprachiasmatic nucleus (hypothalamus), which is involved in setting the body’s circadian rhythms.
What is the bandwidth of blue light?
446-477 nm
What does radiometry have to do with?
Has to do with measurements of electromagnetic radiation, regardless of the eye’s ability to detect it. (Watts)
What does spectrometry have to do with?
Has to do with measurements of electromagnetic radiation that has an effect on the visual system. (Lumens)
Definition of luminous power and its units.
Total light power produced by a source.
Common units: Lumens in joules per second OR watts
Radiometric equivalent: radiant power
Luminous intensity definition and units
Light power produced in a solid angle produced by a point source.
Units: Lumens/steradian or candelas
Radiometric equivalent: radiant intensity in watts/steradian.
Luminance definition and units
Luminous intensity per unit projected area of an extended source.
Units: candelas/ m^2 or foot lamberts
Radiometric equivalent: radiance in watts/steradian/square meter
Illuminance definition and units
Luminous power falling on a surface.
Units: Lumens/m^2 or lumens/ft^2\
Radiometric equivalent: Irradiance in watts/ m^2
A _____ is a unit of radiant power. Its units are measured in ___________.
Watt; joule/second.
It can be a direct measure of output.
A _____ is a unit for luminous power (light output) or a small (“point”) source.
Lumen
Abney’s Law of Additivity
Abney’s Law states that the TOTAL LUMINANCE of a light comprised of a MIXTURE of wavelengths is equal to the SUM of the luminances of all wavelengths in the mixture.
“Lumens are additive”
Incandescent vs Luminescent lightbulbs
Incandescent lightbulbs: generate light through heat. Voltage differential causes filament to get hot, producing heat and light.
Luminescent lightbulbs: generate light through excitation of argon gas. The gas releases UV rays which are absorbed by a phosphor lining which re-emits light in the visible range.
On a black body radiator, what are the x and y xis of spectral distribution of radiation graph.
X: Wavelength (nm)
Y: Spectral emittance (percent of emission)
What relative emission (in K) is recommended for color testing?
6770 K
For brightness matching test, when the two colors appear the same brightness, what is the person adjusting? Why is brightness matching difficult?
The person is adjusting the radiance or luminance to match the brightness of the fixed color. It is difficult for patient because of the color differences between the two stimuli.
How do you find luminous efficiency?
of lumens = watts x 680 lumens/watt (photopic) x luminous efficiency
Solve for luminous efficiency
Luminous efficiency = # of lumens / watts x 680 lumens/watt (photopic)
What is luminous efficiency?
the ratio of the total LUMINOUS power to the total RADIANT power of a source.
Under scotopic conditions, what is the most sensitive wavelength and what is its lumens per watt
507 nm; 1700 lumens
Describe luminous efficacy graph
It shows the absolute sensitivity of the visual system to electro- magnetic radiation is different under photopic vs. scotopic conditions. For anything under 555, the eye is more sensitive to it under photopic conditions.
