optoelectronics chapter 1 terminology. em spectrum
TRANSCRIPT
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Optoelectronics
Chapter 1Terminology
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EM Spectrum
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Terms
• Photometry – visible light – Flux (Power) is in Lumens (lm)– Subscript is “v” for visible light
• Radiometry – non-visible light – Flux (Power) is in Watts (W)– Subscript is “e” for radiant energy
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Particle or Wave?
• Light– Particles – Proposed by Newton in 1666
• Tiny particles called corpuscles
– Waves – Proposed by Huygens during same time– Electromagnetic waves
• Proposed by Maxwell in 1860
– Surfaces emit electrons when exposed to light• Proposed by Hertz in 1887
– Quanta – small packets of energy • Max Planck in 1900
– Light has both Particle and Wave characteristics
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• PhotonsE = h fWhere h = Planck’s constant = 6.63 x 10-34
f = frequency in Hertz– Einstein proposed equation in 1905– Energy from light is directly proportional to
frequency• Speed of Light
C = f λ = 3.0 x 108 m/s
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Radiometric and Photometric Terms
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• Eyes and Ears are not linear. – Logrithmic– Sound intensity measured in Decibels (dBs)– LED can saturate eye’s retinal response in low light– Eye detects certain frequencies much better• Green at 555 nm
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CIE Curve
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• Intensity
• Solid Angle• Ten Diameter Rule
– Distance, d, must be 10 times the diameter of the source– Reduces errors of greater than 10% due to distance
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Photometer
• Photometer– Device to measure visible light parameters• Flux amount of light• Intensity brightness• Incidance
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Intensity Measurements• To measure Intensity of an LED by Two Point Method– If distance from LED is not defined • Make intensity measurement at two different distances.• Only need to know distance between the two measurements.• Photometer reads Ev1 and Ev2
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Standards
• Color Temperature– Tungsten lamp• Used to measure light parameters• Different colors at different temperatures
– NIST – National Bureau of Standards• NIST has the primary standard• NIST gives out secondary standards to use in labs
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