CE3121. Assignement 13

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California Polytechnic State University, Pomona *

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3121

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Physics

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Jan 9, 2024

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Kay Thai 16.1 Natural light is radiant energy from the sun. The visible spectrum ranges from (380 ) to (780 ) nanometers. 16.2 Light generated from electrical light sources (lamps) is radiant energy (True/False). 16.3 The three primary colors of light are (Red, Blue and Yellow ). 16.4 The three subtractive primaries of light are (Magneta, Yello and Cyan). 16.5 What unit of measure is used for illuminance, or illumination level? - footcandles or lux 16.6 Daylight under sunlight is about (10,000) foot-candles. 16.7 Daylight under an overcast sky is about (1000) foot-candles. 16.8 Color temperature is a way to define the heat generated by various types of lamps (True/False). 16.9 What is the approximate color temperature of a gas-filled incandescent lamp? A fluorescent lamp? - Incandescent lamps vary from 3000°K to 3500°K, and 5000°K with a special tinted daylight lamp. - Fluorescent lamps depend on the composition of the phosphors. They could vary from 3000°K to 8000°K. 16.10 What is the conventional unit of measure of light power? What is the SI unit? -Lumens 16.11 What are the normal human responses to various colors? - shorter wavelengths, such as blue through cyan - as cool, calm, peaceful, - medium wavelengths, such as green through yellow - as neutral, harmonious, - longer wavelengths, such as orange through red - as excitement, caution, alarming 16.12 What is the meaning of luminous intensity? -Luminous intensity is defined as the light power or luminous flux (lumens) per unit of solid angle (steradian). A unit of luminous intensity is one candela.

16.13 Color difference also improves visual acuity even if the object and its background are at the same luminance level or zero contrast (True/False). 16.14 A higher luminance contrast is desired for viewing a fast-moving object, such as a baseball, but is not important for a stationary task (True/False). 16.15 Does a high luminance contrast provide more visual comfort? Not necessarily, too high a contrast may cause eye strain. 16.16 What are glare, direct glare, reflected glare, discomfort glare, and disability glare? - Glare is the sensation produced by luminances within the visual field that causes annoyance, discomfort, or loss in visibility. - Direct glare is the glare caused directly by the light sources, such as from the sun or a lamp. - Indirect glare is the glare caused by the reflection surfaces, particularly polished (specular) or glassy surfaces. - Discomfort glare is the glare that produces visual discomfort, but does not necessarily interfere with visual performance. - Disability glare is the intense glare that causes the loss of visibility. - Blinding glare is the intense glare that can cause temporary or permanent blindness. 16.17 A ray of sunlight reaching the earth has a balanced energy level of all visible wavelengths (True/False). 16.18 What wavelength is most sensitive to human eyes? -Yellow-green portion of the spectrum at 555 nm is most sensitive to our eyes. 16.19 White light is a mixture of colored lights (True/False). 16.20 What are the basic characteristics of color? - Hue - the basic color, such as red, yellow, yellow-green, etc. - Value - the shade of color, such as light or dark red. - Chroma - the intensity of color resulting from mixing of saturated color light with white light. 16.21 If 64 lm reach a surface of 10 ft2, what is the illumination level in foot-candles and in lux? E = F / A = 64 / 10 = 6.4fc.

E = 6.4 × 10.78 = 69lux 16.22 What are typical illuminance levels for office occupancies? -50 to 70 foot- candles for general office type occupancies 16.24 A light source having a candlepower of 20 cd illuminates a surface 2 ft away. What will be the illuminance on the source? Illumination E = i /d2 I = candel power of source=20cd d = distance between source and surface= 2ft E= 20/ 22 = 5 fc on the surface 16.26 What are the means of light control? -Reflection, diffusion, transmission, absorption, refraction, and polarization 16.27 Light travels in a straight line in a single medium, such as air, water, or glass (True/False). 16.28 Light always bends the same way between media. (True/False) 16.32 A book is 0.80 ft2 in area and the average lighting power, directly and indirectly, reaching a 4-ft2 desk is 75 lm. What is the illuminance on the book? On the desk? -E = F / A, the illumination on the desk is = 75 / 4 = 19 foot-candles. 16.33 A lighting system consists of 10 spotlights, of which 1 is located directly above a task, and the other 9 are aimed elsewhere. The reflected illuminance from these 9 fixtures is calculated to be 3 fc on the task. What is the illuminance on the task if the candlepower at the center of the spotlight is 2500 cd and the spotlight is 10 ft above the task? E = I / d2 = 2500 / 102 = 25 foot-candles. and the total illuminance from direct and reflected components is: E = 25 + 3 = 28 foot-candles. 16.35 Why do approaching automobile headlights appear so bright at night? 1. Constructive interference 2. Frequency seems more as the car approach

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16.36 How would you describe your visual sensation when the approaching headlights are on low beam? On high beam? -low beam headlight creates a discomfort glare in my field of view, but definitely a disability glare when the car is getting closer and a blinding glare when the car is head on. 16.37 A lamp rated for 1000 lm of light power is installed within a lighting fixture (luminaire). Can all the lumens be utilized to produce useful illumination in the space? -No. Depending on the construction of the lighting fixture, more or less of the light power (lumens) will be absorbed by the interior surfaces of the fixture that eventually degrades into heat. Only a portion of the light power will escape (out of the fixture) to be useful for illuminating the space. 16.38 When a lamp or several lamps are installed in a lighting fixture or luminaire, not all the lamp light power (lumens) may be emitted from the luminaire. If 80 percent of the total lumens are emitted from a luminaire, then the luminaire is said to be 80 percent efficient. Does this mean that 80 percent of the total lamp light power will be utilized on the task anywhere in the room? - Lamp are generally is used a fuel to glow like kerosene and others and it is having 80 percent efficiency because the wattage and the lumens 'initial lumens ' the downward part and the outer wall is make the efficiency 80 percent as compared to 100 percent. And the fuel is used in lamps are also converted liquid to gas directly in the presence of air so, on that the efficiency are also because 80.

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