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Production and Transmission of Light

Production and Transmission of Light. Measurement Light and color production Pigments, interference, scattering, bioluminescence Transmission through the environment Optimal hue, contrast, shading. Color. Light intensity (analogous to sound amplitude). Radiant flux Photons/s

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Production and Transmission of Light

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  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 flux Photons/s • Irradiance Photons/s•m2 • Total light, including scattered and direct • Radiant intensity Photons/s•sr • Radiance Photons/s•sr•m2 • Only direct light emitted from a specific area • sr = steradian with 4p 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 Hue Chroma 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 Benzene absorbs UV Carotene absorbs blue and transmits green, yellow and red 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 Iridiophores contain platelets that reflect some wavelengths Lizards Cephalopods

  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

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