Lec. 28, Thursday, April 22 - colorado.edu€¦ · Lec. 28, Thursday, April 22 ... LCD...
-
Upload
doankhuong -
Category
Documents
-
view
214 -
download
0
Transcript of Lec. 28, Thursday, April 22 - colorado.edu€¦ · Lec. 28, Thursday, April 22 ... LCD...
111
Lec. 28, Thursday, April 22End Chapter 8: Binocular vision
1
We are here
1
Homework is due today in the helproom by 4 pm.
• Stereo images and movies
• Supplementary material– Solar power
• Thermal
• Photovoltaic
– Energy efficient lighting• Fluorescent• LED
– The laser
Faculty Course Questionnaire
2
How do polarized 3‐d glasses work?
1. The two images are projected onto a screen.
2. The light passes through polarizing filters leaning 45 degrees to the left and 45 degrees to the right.
3. The person wears polarizing glasses so each eye sees just one of the images.
4. The projection screen must be special to preserve the polarization.
2
33
Special screen that does not “scramble”polarization
Demo: stereo pairs
What 3d technology was used in Avatar?
1. RealD Cinema uses circular polarization.
2. The electric field direction is rotating either clockwise or counterclockwise. There are filters for circular polarization. This “works” if you tilt your head.
3. A lenticular (silver) screen is used to preserve polarization.
4. Alternate images are projected with different polarization. 48 frames per second is the total.
Cicularly polarized light has the electric field rotating clockwise or counterclockwise.
x
y
z
http://en.wikipedia.org/wiki/Circular_polarization
LCD “shutter” 3d glasses for games
• The LCD panel is either “on”or “off” (clear or opaque)
• Alternate sides are on and off. The left eye sees “even numbered” images and the right side sees “odd numbered” images.
The glasses must have a battery and receive a synchronizing signal.
777
Lec. 28, Thursday, April 22End Chapter 8: Binocular vision
7
We are here
7
Homework is due today in the helproom by 4 pm.
• Stereo images and movies
• Supplementary material– Solar power (textbook p. 104‐106)
• Thermal
• Photovoltaic
– Energy efficient lighting• Fluorescent• LED
– The laser
Solar thermal power (textbook p. 104)
“Thermal” power means the sunlight is used to heat directly (no electricity generation).
Examples:Solar cooker
Solar hot water
Solar home
Solar cooker. Solar hot water
Passive solar home is designed to absorb sunlight and turn it to heat directly.
About power and energy
Energy is the amount of work that can be done.
Metric units for work or energy: Joules
Power company units: kilowatt‐hours
Power is the amount of work done per unit time.
Units: Watts = Joules per second
For comparison: 1 horsepower = 750 watts
Compare to gallons (amount of water) and gallons per minute (coming from the tap).
The numbers for sunlight
Sunlight in orbit: 1380 watts / m2.
It is diminished by atmospheric absorption and nighttime. The sun is lower is higher latitudes.
Daily average in Boulder:
160 watts / square meter.
Average solar irradiance
The black dots are the area needed to generate all of the electricity from 8% efficient solar cells. 13
Solar Power Tower
Flat mirrors (heliostats) are steered to direct sunlight at a boiler on a tower.This plant generates 5 MW and is in the desert in California. 14
Solar Power Parabolic Trough
Sunlight is concentrated on a pipe containing a fluid with a high boiling point. This fluid goes to a heat exchanger that boils water. There are 5 generating stations in California with 33 MW capacity. The parabolic mirror is tilted to follow the height of the sun.
15
Solar photovoltaic
• Generates electricity from sunlight.
16
Solar electric conversion efficiency
Typical conversion efficiency
=12% – 18%
Final answer = 20 W/m2
daily average of electric power.
For 24 hrs. = 480 watt‐hours Array of solar cells
How does it work?
Solar photons excite electronsto higher energy level Electric current flows as
the electrons seek a lower level.
Electric current returns to semiconductor
Photovoltaic cells are made of semiconductors with energy levels for electrons.
18
Solar photovoltaic numbers
24 hr. average at ground level: 160 W/m2.
Assume 13% efficiency: 20 W/m2 of electricity.
24 hrs. x 20 W/m2 = 0.5 kW‐hrs/m2.
Small home usage: 20 kW‐hrs each day.
Conclusion: home needs 40 m2 of panels.
[About 20 feet square. A large part of a roof.]
19
Why aren’t solar panels everywhere?
• They only work in daytime, so battery storage is needed with additional cost and DC to AC converters.
• A complete system is expensive. About $10 per watt. A 1 kW system costs $10,000.
20
212121
Lec. 28, Thursday, April 22End Chapter 8: Binocular vision
21
We are here
21
Homework is due today in the helproom by 4 pm.
• Stereo images and movies
• Supplementary material– Solar power
• Thermal
• Photovoltaic
– Energy efficient lighting• Fluorescent• LED
– The laser
What is energy efficiency?
• Light out is measured in lumens.
• Power used is measured in watts.
• More lumens/watt is better.
• Indoor lighting options– Compact fluorescent
– LED (light emitting diode)
22
Incandescent lighting
• Electricity heats a tungsten filament.
The filament glows emitting heat and light. Efficiency: 15 lumens/watt
Lifetime: 1,000 hours
• Halogen lamps have a hotter tungsten filament and produce more light.
Efficiency: 20 lumens/watts
23
Spectrum of incandescent source
24
Incandescentlamp
Compact fluorescent lighting
• CFLs go in standard sockets• They contain a small amount of mercury (Hg).
• Lifetime: 10,000 hrs. • Efficiency: 60 lumens/wattHow it works: Hg atoms are excited by the current and emit UV photons.
UV photons hit the phosphor coating that emits white light.
25
Spectrum of a fluorescent lamp
26
The peaks in the spectrum are from different chemical elements in the phosphor.
LED lighting (light emitting diodes)
• Emit a single color
• Lifetime 10,000 hrs.
• White is generated by combining colors or by using UV and a phosphor
• Efficiency: 25 lumens/watt
(100 lm/W in the lab)
27
How do LEDs work?
Electrons in the semiconductoremit photons.
Electric current drives the LED 28
Battery
+
‐
Light output Electron
Spectrum of LED lamp
29
Blue LED with phosphor. Red, green, and blue LEDs.
Laser light source
A laser has a cavity defined by two mirrors that reflects light back on itself. The optically active material amplifies the light. Hence, Light Amplification by Stimulated Emission of Radiation.
30
Mirror Partially silvered mirror
Ruby rod, for example
Incident pump photons can “pump up” electrons which emit light.
Coherent light
Laser materials
• Gases– helium‐neon laser (some supermarket scanners)
– Argon laser (some laser light shows)
• Liquids, dye laser
• Solids– Ruby laser– Laser diode (like an LED)
31Gas laser
Laser diode for laser pointer
Spectrum of a laser
32
The wavelength is known precisely, so lasers are used for precision measurements.
This spectrum is for the helium-neon laser.