Light and Colour LIGHT & SOUND - PowerPoint Presentation

1. Light and ColourLIGHT & SOUNDINTD 302ASSOC PROF DR NOOR HANITA ABDUL MAJID

2. Photopic: color vision takes palace under bright conditions

3. Revision-what happens in the eyes?1. Light from an external object is refracted as it moves through the cornea, 2. moves on to the pupil-controlled by the iris. 3.light is again refracted by the lens, which projects an upside-down image on the retina4. absorbed by pigments in light-sensitive cells, called rods and cones. These photoreceptors convert light (photons) into electro-chemical signals, which are then processed by neural circuits in the retina and transmitted to the brain.123

4. Photoreceptor cells - absorb light and generate nerve signals Rods very sensitive to dim light no color information => no color vision in dim light Sensitive to the blue-green portion of the visible spectrumCones less sensitive to dim light provide color information three types red - peak sensitivity to red light green - peak sensitivity to green light blue - peak sensitivity to blue light incoming light excites all three types to some extent - giving a perception of all colors

5. Human Eye: Rods and ConesS cones (blue)M cones (green)L cones (red)rods (overall intensity)Near foveaNear periphery

6. At the retina……approximately 6 million cones in our retina, and they are sensitive to a wide range of brightness. The three different types of cones are sensitive to short, medium and long wavelengths, respectively. Cones are active at high light levels and allow us to see color and fine detail directly in front of us. They can adapt to widely varying colors and illumination levels, but don’t work well in low light.approximately 125 million rods are used only in dim light, and are monochromatic, so they don’t perceive color — only black and white.

7. visionPhotopic: color vision in relative high brightness conditionsMesopic: vision that takes place typically during dusk or dawn 2.2 to 20 lux.Scotopic:vision at very low brightness (2.2 lux-0.5 lux(full moon))

8. Color visionFor typical healthy eyesBlue objects are focused in front of fovea-lens will be less convex = objects appear farRed objects are focused behind the fovea- less will be more convex=objects appear closerIn design…to make objects appear closer (warm color advance)or farther (cool color recede)..

9. What is color ? physicist: wavelength of a light wave biologist: neural response in the eye psychologist: perception in brain artist: tool to express feelings linguist: language restricts our ability to describe "color" -some languages have no color terms

10. What are the basic colors ?Three primary colors subtractive color mixing: Red, Yellow, Blue subtractive color mixing: works by absorbing other colors food coloring, paints if you mix all colors - you get black additive color mixing: Red, Green, Blue combines colors excites eye to make you think you see the resultant color if you mix all colors - you get white

11. There is an important difference between lights and pigmentsLights mix additively. The more lights you add to the mix, the closer you get to white light.Pigments (paints, etc) mix subtractively. The more colors you add, the closer you get to black. This is because pigments absorb light. The more pigments you add, the more light will be absorbed. Here's an example of how blue and yellow pigments combine to give green.

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14. What are colors? Light varies in both intensity and wavelength. Light of different wavelengths appears to us to have different colors. Intensity is the amplitude or height of a sinusoidal wave. Brightness is our perception of the intensity of light.Wavelength is the distance between two peaks of a wave.

15. There are three Attributes used to describe Color.HueA technical term for color. Red, yellow, blue, orange, pink are all hues. White, gray and black have no hue.Saturation/chroma or intensityColor purity. Higher saturation means richer, stronger colors. Lower saturation means grayer or more washed out colors. Saturation is inversely related to the amount of whiteness in a color. The more saturated a color, the less whiteness it contains. For example, red is more saturated than pink. ValueThe overall Lightness or Darkness of a color. A highly saturated Yellow is likely to have a much lighter Value than a highly saturated Blue.

16. Color RenditionThe ability to see colors properly is another aspect of lighting quality. Light sources vary in their ability to accurately reflect the true colors of people and objects.The color rendering index (CRI) scale is used to compare the effect of a light source on the color appearance of its surroundings.A scale of 0 to 100 defines the CRI. A higher CRI means better color rendering, or less color shift. CRIs 75-100 –excellent65-75 –good55-65 –fair0-55 is poorUnder higher CRI sources, surface colors appear brighter, improving the aesthetics of the space. Sometimes, higher CRI sources create the illusion of higher illuminance levels.

17. Dispersion-revision A property of light. ability to break white light into its constituent colors. White light consists of all of the colors we are able to see. If white light enters a prism, what emerges from the other side is a spread out beam of multi-colored light. Blue light, with longer wavelengths, gets bent more by the different angles of the prism than red light, and the other colors are in between blue and red on the wave spectrum.

18. White light is composed of all wavelengths of the visible spectrum. Newton was the first to show this by passing sunlight through a prism. Light passed through a prism is broken down into a "rainbow" spectrum.Why is that? Because lights of different wavelengths have different refractive properties. Long-wavelength (red) light is bent least by passing through a prism, while short-wavelength (blue) light is bent most (remember chromatic aberration?). Objects have different colors because they reflect different wavelengths of light.

19. This image (when viewed in full size, 1000 pixels wide) contains 1 million pixels, each of a different color. The human eye can distinguish about 10 million different colors

20. What colors do we see? Chromatic and Achromatic color Black, white, and the shades of gray in between are achromatic colors. Achromatic colors have approximately equal power across all the wavelengths in the visible range. In dim light, we only see achromatic colors. Blue, red, green, and yellow are all examples of chromatic colors. These are the colors we see in good light using our cones.

21. Does purple belongs to blue or red? Where is its location on the color wheel?

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25. Color deficits

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28. Color OpponencyThe color purple looks both reddish and blueish. The color orange looks both reddish and yellowish. Turquoise both blueish and greenish. But you've never seen a color that looks both green and red. Nor have you ever seen a color that looks both yellow and blue. Hering (another 19th century psychophysicist) to propose the opponent colors theory of color perception.

29. Color opponency was established with the hue cancellation experiment, in which subjects were instructed to adjust a mixture of red and green lights until it appeared neither redish nor greenish. At this point, it typically appeared yellow (notable, not redish-greenish). Likewise, one can adjust a mixture of blue and yellow lights to appear neither blueish nor yellowish

30. Trichromacy falls out from the fact that you have three cone types with different spectral sensitivities. In the retina, the cone signals get recombined into opponent mechanisms: White/black: adds signals from all three cones types, L+M+S. Red/green: L-M Yellow/blue: L+M-S A color appears reddish when the red/green mechanism gives a positive response, greenish when the red/green mechanism gives a negative response. Likewise for yellow/blue.

31. Color Constancy and Chromatic AdaptationTake a photograph under flourescent light, and compare it to the same picture taken under daylight. The colors come out totally differently - greenish under the flourescent light and reddish under daylight - unless you do some "color correction" while developing the film.

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33. Glance at the penguin and dragon pictures above by fixated on the dot between them. The penguin picture looks very blueish and the dragon looks very yellowish. Next, you will hold your gaze on the dot between the blue and yellow fields. Continue staring at that dot for 30 secs or so. Then look back at the penguin and dragon by fixating the dot between them. What do you see? Why?

34. The change in percept following adaptation is due to chromatic adaptation. Chromatic adaptation is like light and dark adaptation but instead of adapting just to light and dark, it adapts to whatever the color is of the ambient illumination.

35. Perception: Color ConstancyHumans are very good at recognizing the same materialcolors under different illumination.

36. Light Color Characteristicstwo systems of measurement commonly used to describe the color properties of a light source: color temperature-which expresses the color appearance of the light itselfcolor rendering index(CRI)-which suggests how an object illuminated by that light will appear in relation to its appearance under other common light sources.

37. Colour qualities and light structure The colour qualities of a lamp are characterised by two different attributes: (a) its colour appearance described by its colour temperature; and (b) its colour rendering capabilities which affect the colour appearance of objects illuminated by the lamp. The colour appearance of a lamp refers to the apparent colour of the light and may be indicated by its correlated colour temperature. It is the temperature of the blackbody whose chromaticity most resembles that of the light source. White light sources may be loosely divided into three groups according to their colour appearance, as shown in Table below: Three groups of white light sources Colour appearance Correlated colour temperature (CCT) Cold (bluish white) 5300 K < CCT Intermediate (white) 3300 K < CCT <= 5300 K Warm (reddish white) CCT <= 3300 K

38. Color TemperatureLamps can be described as “Warm” or “Cool” based on whether they are yellowish white or bluish white. Color Temperature (measured in Kelvins) is a scientific scale to describe how warm or how cool the light source is. As a piece of metal is heated, it will go through the color changes shown on the left. We can use this scale to describe the “Color Temperature” of a light source.When we say a lamp has a Color Temperature of 3000 Kelvin, it means a glowing metal at 3000 Kelvin would produce light of about the same color as the lamp. Instead, if the metal is heated to 4100 Kelvin, it will produce a much whiter light.

39. Color Rendering Index (CRI)Color Rendering Index (CRI) of a lamp tells us how rich colors look under the lamp. Two lamps may have the same Color Temperature but they can render colors differently. Daylight is assigned a CRI of 100 and lamps are assigned a CRI number to indicate how rich colors look.Daylight = 100 CRIBest fluorescent = 85-90 CRIOld T12 fluorescent = 62 CRIHPS (street lights) = 22 CRIHalogen & incandescent = 100 CRI

40. Good lightingis achieved when a meaningful place is created that meets the users visual needs. A lighting system that employs specific patterns of light and shade to reinforce selected information or room characteristics will be successful in creating meaningful places. In order to use this, a clear understanding of how light affects perceptions; impressions; behavior; and mood is necessary.

41. The choice of an appropriate apparent colour of light source for a room is largely determined by the function of the room. This may involve such psychological aspects of colour as the impression of warmth, relaxation, clarity, etc., and more practical considerations such as the need to have a colour appearance compatible with daylight. The appearance of coloured surfaces is controlled by the spectral power distribution of the light source. For example, a red rose will only appear red if the appropriate wavelengths of light are reflected from it. Taking the range of possible surface colours as a whole, the power balance and presence or absence of certain wavelengths in the incident light causes differences in colour rendering under different sources.

42. Psychological techniques have been used in lighting research to develop light structure models for use by designers. The concept of light structure is based on the notion that the experience of room lighting is, in part, an experience of recognising and assimilating complex lighting pattern. It suggests that different pattern aspects of light interact and convey information about the visual world. The brain constructs an impression of the phenomenal world from this information. This concept of information content and "meaning" further indicates that lighting should be considered not merely as a stimulus but also as a "structure".

43. Table Y: shows a lighting design guide that may help the designer achieve specific subjective impressions with different lighting design strategies.

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