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Commission Internationale de l’Eclairage (CIE)

Where vision is concerned, light is generally specified in photometric units, not in quanta (photons) and energy. Commission Internationale de l’Eclairage (CIE).

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Commission Internationale de l’Eclairage (CIE)

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  1. Where vision is concerned, light is generally specified in photometric units, not in quanta (photons) and energy

  2. Commission Internationale de l’Eclairage (CIE)

  3. Fig. A-1. The photopic (V) and scotopic (V’)curves of relative luminosity as standardized by the Commission Internationale de l’Eclairage (CIE). Modified from Wright (1958)

  4. Just because something is twice as intense does not mean it is twice as bright!!

  5. Luminous flux Luminous intensity iIluminance is emitted is is what in all directions from a luminous flux in a solid falls on a surface. It is candela lumens/ point source of light. A angle. A is measured in A lumen unit area is equivalent to defined as one lumen/ 15 4.07 x 10 quanta/ second steradian. at 555 nm. q Luminance is the light that comes off a surface whether Point reflected or emitted. Source It is measured in candelas/unit area B r Photometric Terminology

  6. A steradian is "the solid angle subtended at the center of a sphere of radius r by a portion of the surface of the sphere having an area r2."

  7. Fig. A.2 Luminous flux Luminous intensity iIluminance is emitted is is what in all directions from a luminous flux in a solid falls on a surface. It is candela lumens/ point source of light. A angle. A is measured in A lumen unit area is equivalent to defined as one lumen/ 15 4.07 x 10 quanta/ second steradian. at 555 nm. q Luminance is the light that comes off a surface whether Point reflected or emitted. Source It is measured in candelas/unit area B r

  8. Luminous flux Luminous intensity iIluminance is emitted is is what in all directions from a luminous flux in a solid falls on a surface. It is candela lumens/ point source of light. A angle. A is measured in A lumen unit area is equivalent to defined as one lumen/ 15 4.07 x 10 quanta/ second steradian. at 555 nm. q Luminance is the light that comes off a surface whether Point reflected or emitted. Source It is measured in candelas/unit area B r

  9. Luminous flux Luminous intensity iIluminance is emitted is is what in all directions from a luminous flux in a solid falls on a surface. It is candela lumens/ point source of light. A angle. A is measured in A lumen unit area is equivalent to defined as one lumen/ 15 4.07 x 10 quanta/ second steradian. at 555 nm. q Luminance is the light that comes off a surface whether Point reflected or emitted. Source It is measured in candelas/unit area B r

  10. Luminous flux Luminous intensity iIluminance is emitted is is what in all directions from a luminous flux in a solid falls on a surface. It is candela lumens/ point source of light. A angle. A is measured in A lumen unit area is equivalent to defined as one lumen/ 15 4.07 x 10 quanta/ second steradian. at 555 nm. q Luminance is the light that comes off a surface whether Point reflected or emitted. Source It is measured in candelas/unit area B r

  11. Luminous flux Luminous intensity iIluminance is emitted is is what in all directions from a luminous flux in a solid falls on a surface. It is candela lumens/ point source of light. A angle. A is measured in A lumen unit area is equivalent to defined as one lumen/ 15 4.07 x 10 quanta/ second steradian. at 555 nm. q Luminance is the light that comes off a surface whether Point reflected or emitted. Source It is measured in candelas/unit area B r

  12. Photopic Mesopic Scotopic

  13. - (L L ) /L T B B Contrast is not a photometric term. Contrast is an expression of luminous difference between two surfaces . The standard quantitative definition of contrast for a target on a background is: Eq. A.4 where L is the luminance of the ref erence surface and L is the luminance of the B T second surface. If L > L then the contrast is positive; otherwise it is negative. T B “ Weber Contrast ” This is sometimes called

  14. The contrast of sine-wave gratings is measured differently Fig. 6.6

  15. Sine-wave gratings are measured in terms of their spatial frequency defined as the number of cycles per degree of visual angle Fig. 6.7

  16. Specifying and Using Visual Angle Stimulus size is often expressed in terms of visual angle Fig. A.3

  17. Specifying and Using Visual Angle • Stimulus size is often expressed in terms of visual angle • Two advantages: • Provides a measure of the stimulus size on the retina • That allows investigators in other labs to duplicate the stimulus size (without needing to duplicate the equipment)

  18. Objects A and B are the same size, but subtend different angles on the retina because they are at different distances from the cornea Object C subtends the same angle as object A, so A and C would be indistinguishable based on retinal size and position alone Can calculate the visual angles subtended by the visual stimuli:

  19. Visual angles are expressed in degrees, minutes or seconds of arc Large stimuli subtend visual angles expressed in degrees () (e.g., a 10 spot) There are 360 in a circle Smaller stimuli are described in minutes (’) of arc There are 60’ in 1 of arc Still smaller stimuli are expressed in second (”) of arc There are 60” in 1’ of arc

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