Radiometry and Photometry Lecture Flashcards
How are wavelengths and Hz related
Short wavelength= smaller number = higher Hz
Longer wavelength= higher number = lower Hz
Difference between UV A, B and C
A: 320-400 nm. gets through the atmosphere most easily.
B: 280 to 320 nm. Light isn’t passed through the atmosphere easily
C: 200-280 nm. Light that is most absorbed by the ozone layer, but most dangerous to us.
How can infrared light be used to help with optometry
Special glasses made to help measure pupil size of those with really dark irises.
Are all species visually sensitive to the same wavelengths?
No. Ex: bees barely detect red. Hummingbirds detect more color than us.
Photons act in waves to create an
Interference pattern rather than a banding, which is what would be expected.
Hue is determined by
Wavelength
UV A, B, and C and eyes
UV C is mainly absorbed by a normal, healthy cornea. Too much exposure leads to UV keratitis or keratoconjunctivitis. Very painful.
UV A and B absorption over the years is cause of cataracts.
UV exposure can also lead to basal cell carcinoma of eyelid skin.
When exposed to sunlight, how does this affect the circadian rhythm?
When retinal ganglion cells containing melanopsin are stimulated by sunlight, it sends info to the suprachiasmatic nucleus in the hypothalamus. Involved in setting circadian rhythm.
Short wavelength light is potentially more damaging than longer wavelengths, but we need exposure to short to help regulate circadian rhythms and functions associated such as brain activity, hormone activity and cell regenerate.
Normal light conditions- No malanopsin response
Bright light or sunshine- Melanopsin becomes active
Radiometry is measured in ___ and photometry is measured in___
Radiometry- watts
Photometry- Lumens
Two radiometrically equivalent stimuli can be photometrically different
Why aren’t incandescent bulbs efficient light sources?
80% efficient bulb? Then the bulb mitts 80% of its wattage as radiant flex.
Incandescent bulbs are not efficient light sources because of this 8-% radiant flux, 75% of it is infrared.
Relation between lumen and watt
A lumen is equivalent to a watt, it just considers wavelength dependent eye sensitivity and adjusts for it.
Abney’s Law of Additivity
States that the total luminance of a light comprised of a mixture of wavelengths is equal to the sum of the luminance of all wavelengths in that mixture. AKA lumens are additive.
Characteristics of incandescent bulbs and what are they typically made of?
Light is generated through heat. There is a voltage differential across the filament that raises the temp and produces light.
Typically made of halogen compounds.
Why is it important to keep lighting conditions the same in the exam room?
So patients are tested in the same environment day to day and year to year.
Think about how it would affect VAs.
3 methods to measure wavelength sensitivity
- Brightness matching
- Comparing the standard 555 nm wavelengths against another. Comparison wavelength is adjusted until the observer notes equal brightness from both stimuli. Highly variable. - Heterochromic flicker photometry
- Standard wavelength is alternated with a comparison wavelength. Creates flicker which means that the magnitudes of the two stimuli’s luminance are not equal. Observer adjusts until the flicker stops. Reliable and follows Abney’s law of additivity. - Minimally distinct border
Standard wavelength with fixed radiance is next to a comparison wavelength with adjustable radiance. The comparison is adjusted until the visibility of a border is barely there. Also reliable, follows Abney’s law of additivity.
