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A different theory for color vision B.Demo: Low Pressure Sodium Lamp 1.Color is totally mental!a.It’s a construction of our psychologyLow pressure sodium lamp emits only one wavelength of light2.a.Everything looks like the sepia filter! b.We turned off all other light and only allowed the yellow light to come through c.Only yellow items appeared yellow because the light reflected into our eye is yellow d.All other objects were some shade of gray C.Color and Light 1.Color signals help us classify and identify objects 2.Color facilitates perceptual organization of elements into objects Color vision may provide an evolutionary advantage in foraging for a.food 3.Electromagnetic Spectrum Visible light wavelengths between 400-700 nanometersa.Infrared spectrum in range of 1,000-100,000 nanometers (felt as heat)b.c.Ultraviolet below 200 nanometers (sunburns us) 4.How do we perceive color? a.Actually, there are no colors out there in the world. Color is not a physical property but a psychophysical property. Color perception is due to our sensory b.interpretation of information in the electromagnetic spectrum –we interpret different wavelengths as different colors c.“There is no red in a 700nm light, just as there is no pain in the hooves of a kicking horse.”—Steven Shevell (2003) d.White light contains all the colors we see e.Rainbows –raindrops split the white light (like a prism) and we see colors 5.Visible Spectrum a.Ultraviolet Vision i.Bees can see in ultraviolet, this is how they see calla lilies contrast: ii.The pistol of the flower is highlighted because that’s the important part for the bee (much sharper target) find more resources at oneclass.comfind more resources at oneclass.com
(Ultraviolet; Infrared ) b.Infrared Vision i.Snakes and vipers can detect infrared light (heat) 6.Light Interacts with Matter a.Chromatic colors or hues –objects that preferentially reflect some wavelengths (selective reflectance) i.Reflectance–the light that bounces off an object into our eye b.Achromatic colors–contain no hues; white, black, gray tones (based on brightness) Whitec.–reflects all wavelengths of light d.Gray- reflects some of all wavelengths e.Black–absence of light being reflected off an object; absorbs all wavelengths of light f.Cyan–reflect blue and green (S, M), absorbs red (L) g.Yellow–absorbs red and green (L, M); absorbs blue (S) h.Magenta–reflects blue and red (S, L); absorbs green (M) 7.Reflectance a.Spectral Reflectance Curves–objects in the real world reflect light across the spectrum in different amounts (not usually single wavelengths)b.When white light shines on a colored object, some photons absorbed, and others reflected by the object’s surfacei.Color is so complicated and complex ii.This graph shows the various wavelengths that can be absorbed and reflectedD.Color Mixing: Lights vs Paints 1.Additive Color Mixture: a.Mixing lights of different wavelengths b.All wavelengths are available for the observer to see Adding wavelengths of light togetherc.d.