Colour theory

additive colur theory , subtractive theory , munsell ,oswalt law

1. Building Technology (Electrical ) UNIT - IV BUDHA COLLEGE OF ARCHITECTURE SUBMITTED BY GAURAV VASHISHTH COLOR THEORY ADDITIVE COLOR THEORY SUBTRACTIVE COLOR THEORY MUNSELL COLOR THEORY OSTWALD COLOR THEORY SODIUM VAPOR LAMP MERCUARY VAPOR LAMP

2. COLOR THEORY Color is the byproduct of the spectrum of light, as it is reflected or absorbed as received by the human eye and processed by the human brain. COLOR TERMS Hue : another name for color Tint : color + white Tont : color + gray Shade : color + black Value : brightness or darkness of the color Saturation : the purity of the color. THERE ARE 12 HUES . ANY OTHER COLOR IS A TINT, TONE OR SHADE ONE OF THESE HUES , UNLESS IT IS A NATURAL. COLOR WHEEL The color wheel is a visual representation of color theory: According to color theory, harmonious color combinations use any two colors opposite to each other on the color wheel, Any three colors equally spaced around the color wheel forming a triangle, A color wheel or  color circle is an organization of color hues around a circle, which shows the relationships between primary colors, secondary colors, tertiary colors OR

3. PRIMARY COLORS ˚ = Red 120 ˚ = Green 240˚ = Blue Visual subtractive primaries: Cyan, magenta, yellow (CMY ) . The basic colors that can be mixed to make all other colors. The primary colors cannot be made by combining other colors. SECONDARY COLORS 60˚ = Yellow 180˚ = Cyan 300˚ = Magenta Colors that are made by mixing two adjacent primary colors . For example, red and blue light mixed give magenta light. Mixing secondary colors: Orange, violet, and green. Visual additive secondary colors: Cyan, magenta, and yellow (CMY ) Visual subtractive secondary colors: Red, green, blue ( RGB ) . Mixing primaries: Red, yellow, blue (RYB) Visual additive primaries: Red, green, blue (RGB) TERTIARY COLOURS Intermediate, or Tertiary, colors are created by mixing a primary and a secondary Red- Orange 4. Blue-Green Orange- Yellow 5. Blue-Purple Yellow- Green 6. Red-Purple

4. COMPLEMENTARY COLORS Complementary colors sit opposite each other on the color wheel. Because they are opposites, they tend to look especially lively when used together. When complementary colors put together , each color looks more noticeable . Red and green are an example of complementary colors . ANALOGOUS COLORS Analogous colors sit next to each other on the color wheel. They tend to look pleasant together because they are closely related . Orange, yellow-orange, and yellow are an example of analogous colors NEUTRAL COLORS Neutral colors don't usually show up on the color wheel. Neutral colors include black, white, gray, and sometimes brown and beige. They are sometimes called “earth tones .” WARM COLORS Warm colors are made with red, orange, yellow, or some combination of these. Warm colors tend to make you think of sunlight and warmth. COOL COLORS Cool colors are made with blue, green, purple, or some combination of these. Cool colors might make you think of cool and peaceful things, like winter skies and still ponds.

5. TYPES OF COLOUR THEORIES SUBTRACTIVE THEORY The subtractive, or pigment theory deals with how white light is absorbed and reflected off of colored surfaces. Black absorbs most light White reflects most light Colored Pigments absorb light and reflect only the frequency of the pigment color. All colors other than the pigment colors are absorbed so this is called subtractive color theory. The primary colors in Subtractive Theory are: Cyan ( C ) Yellow ( Y ) Black( K ) Magenta( M ) Subtractive or Pigment Theory is used in printing and painting. ADDITIVE THEORY The additive, or light theory deals with radiated and filtered light. Black radiates no light White (sun) radiates all light Video is the process of capturing and radiating light, therefore it uses Additive (Light) Theory not Subtractive (Pigment) Theory . The primary colors in Additive Theory are: Red ( R ) Blue( B ) Green( G ) The primary colors add together to make white Light Theory is also called Additive Theory. Light Theory is used in Television, theater lighting, computer monitor.

6. MUNSELL COLOR THEORY The Munsell Color Order System is a three-dimensional model based on the premise that each color has three qualities or attributes: hue, value and chroma Munsell established numerical scales with visually uniform steps for each of these attributes. Using the Munsell nomenclature HV/C, our vivid red example would have the Munsell notation 5R 6/14. 5R is the hue (red), 6 is the value (moderately light), and a 14 chroma indicates a highly chromatic color . The notation for a neutral color is written: NV The chroma of a neutral color is zero, but it is customary to omit the zero in the notation . The notation N 1/ denotes a black, a very dark neutral, while N 9/ denotes a white, a very light neutral. This notation for a middle gray is N 5/.

7. OSTWALD COLOUR THEORY The Ostwald system creates a color space based on dominant wavelength, purity, and luminance, mapping the values of hue, saturation and brightness. Establishing the values for these parameters is done with a disc colorimeter which mixes on a disk amounts of the pure spectral color at the dominant wavelength with white, and black . Thus the point in the Ostwald color space is represented by values C,W, and B to represent the percentages of the circle. The full colors are arranged around a complete circle  starts out with four basic colors: yellow to the north; red to the east; blue to the south; and sea-green to the west . With these eight colors, Ostwald constructs 24 color-hues with equal spacing and numbers them from yellow upwards, arranging them into a circle .

8. SODIUM-VAPOR LAMP A sodium-vapor lamp is a gas-discharge lamp that uses sodium in an excited state to produce light. There are two varieties of such lamps Low pressure High pressure Low-pressure sodium lamps are highly efficient electrical light sources, but their yellow light restricts applications to outdoor lighting such as street lamps High-pressure sodium lamps produce a broader spectrum of light than the low-pressure lamps, but they still have poorer color rendering than other types of lamps Low-pressure sodium lamps only give monochromatic yellow light and so inhibit color vision at night LOW-PRESSURE SODIUM Low-pressure sodium (LPS) lamps have a borosilicate glass gas discharge tube (arc tube) containing solid sodium, a small amount of neon, and argon gas in a Penning mixture to start the gas discharge. The discharge tube may be linear or U-shaped When the lamp is first started, it emits a dim red/pink light to warm the sodium metal; within a few minutes as the sodium metal vaporizes the emission becomes the common bright yellow These lamps produce a virtually monochromatic light averaging a 589.3 nm wavelength .

9. HIGH-PRESSURE SODIUM High-pressure sodium lamps are commonly used as plant grow lights. They have also been widely used for outdoor area lighting such as streetlights and security.  High-pressure sodium lamps are quite efficient—about 100 lm/W. The higher power lamps (600 W) have an efficiency of 150 lm/W. Because the high-pressure sodium arc is extremely chemically reactive, the arc tube is typically made of translucent aluminum oxide Xenon at a low pressure is used as a "starter gas" in the HPS lamp. It has the lowest thermal conductivity and lowest ionization potential of all the non-radioactive noble gases. As a noble gas, it does not interfere with the chemical reactions occurring in the operating lamp THEORY OF OPERATION An amalgam of metallic sodium and mercury lies at the coolest part of the lamp and provides the sodium and mercury vapor that is needed to draw an arc.  The temperature of the amalgam is determined to a great extent by lamp power.  The higher the lamp power, the higher will be the amalgam temperature The higher the temperature of the amalgam, the higher will be the mercury and sodium vapor pressures in the lamp and the higher will be the terminal voltage.

10. As the temperature rises, the constant current and increasing voltage consumes increasing energy until the operating level of power is reached. For a given voltage, there are generally three modes of operation: The lamp is extinguished and no current flows. The lamp is operating with liquid amalgam in the tube. The lamp is operating with all amalgam evaporated. The first and last states are stable, because the lamp resistance is weakly related to the voltage, but the second state is unstable. Any anomalous increase in current will cause an increase in power, causing an increase in amalgam temperature, which will cause a decrease in resistance, which will cause a further increase in current The light from the lamp consists of atomic emission lines of mercury and sodium, but is dominated by the sodium D-line emission. This line is extremely pressure (resonance) broadened and is also self-reversed because of absorption in the cooler outer layers of the arc, giving the lamp its improved color rendering characteristics. Day time Night time

11. MERCURY VAPOR LAMPS The mercury vapor lamp is a high intensity discharge lamp. It uses an arc through vaporized mercury in a high pressure tube to create very bright light directly from it's own arc. Advantages: - Good efficiency (lamps after 1980s have a high lumen per watt rating) - Color rendering is better than that of high pressure sodium street lights - Some lamps last far longer than the 24000 hour mark, sometimes 40 years Disadvantages: - Like many lamps it contains traces of mercury which must be disposed of properly - HPS streetlights have a better lumen per watt rating - Human skin looks green under the light, it is poor for color film/photography -Warm up time required to start the lamp LOW PRESSURE The first mercury vapor lamps were in a lower pressure tube. One would tip the lamp, and electrical contacts on each side of the lamp would send electricity through a liquid mercury which started the lamp. After that the lamp would heat fast and mercury became a vapor. The light would intensify as the arc grew stronger in the tube.

12. HIGH PRESSURE Lamps of today are high pressure lamps with a fused quartz inner discharge tube. This lamp start with a small arc between the starting electrode and the main electrode. This arc goes through argon gas which easily strikes, even in cold weather. This little arc heats the tube, and over several minutes the tube gets hot enough to vaporize the solid mercury stuck to the sides. The mercury vaporized creates a strong light between the two main electrodes. To prevent the arc from infinitely getting stronger a ballast limits the current. Some lamps are  "Self Ballasted" , they use an incandescent filament to act as a resistor, limiting current. Home lighting fixtures usually use the self-ballasted type where as the more expensive but more efficient ballasted lamps are found in large fixtures for municipal lighting