1. Production and Transmission of Light Measurement Light and color production –Pigments, interference, scattering, bioluminescence Transmission through the environment Optimal hue, contrast, shading

2. Color

3. Light intensity (analogous to sound amplitude) Radiant fluxPhotons/s IrradiancePhotons/s m 2 –Total light, including scattered and direct Radiant intensityPhotons/s sr RadiancePhotons/s sr m 2 –Only direct light emitted from a specific area –sr = steradian with 4  steradians in a sphere –Note that intensity is independent of wavelength –But wavelength is inversely related to energy

4. Light intensity variation

5. Color Spectra HueChroma Intensity

6. Color has 3 dimensions Brightness = radiance

7. Sources of color Pigments –Molecules which selectively absorb photons of some wavelengths and transmit others –Size of molecule affects wavelength absorption –Short chain molecules require high energy (short wavelengths) for excitation Structural colors –Interference –Scattering

8. Pigments Carotene absorbs blue and transmits green, yellow and red Benzene absorbs UV Porphyrins: iron = hemoglobin, magnesium = chlorophyl

9. Carotenoids

10. Melanin Large protein that absorbs all wavelengths and, therefore, appears black Present in skin and hair of mammals, chitin of many insects Coat color variants are caused by temporal regulation of melanin production during hair follicle growth, e.g. agouti phenotype: dark-light-dark

11. Status badges in Harris sparrows

12. Chromatophores Fish Lizards Cephalopods Iridiophores contain platelets that reflect some wavelengths

13. Chameleons can change color

14. Cuttlefish have chromatophores

15. Structural colors Color depends on the reflection angle from feathers

16. Interference

17. Interference in feathers

18. Beetles coat melanin with wax

19. Color by Scattering

20. Color by scattering

21. Bioluminescence Bioluminescence is common among marine organisms, especially deep-sea fishes.

22. Habitat Transmission Amount and spectral composition of available light can differ by habitat Color brightness of an object depends on wavelengths of available light In terrestrial habitats, light spectra is influenced by –Sun’s angle, weather, vegetation Expect animals to utilize colors appropriate for habitats

23. Color filtering by habitat Spectra in forest Colors in white light Colors in forest

24. Light reflectance

25. Light attenuation Light attenuation follows inverse square law which is independent of wavelength Scattering and absorption, however, increases as wavelength decreases

26. Signal detection Must discriminate object from background using brightness, color, pattern or movement Can adopt countershading or reverse counter shading for crypsis or conspicuousness Visual systems often exaggerate contrast to detect objects in background

27. Signalling may vary with habitat Phylloscopus warblers

28. Counter and reverse shading

29. Pattern contrast

30. Photon noise

31. Eye resolution

32. Shape enhancement

33. Optimal signal and background hues

34. Mammalian Eye

35. Rods and Cones