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Published byDoreen Daniel Modified over 9 years ago
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Optoelectronics Chapter 1 Terminology
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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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Photons E = h f Where 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 10 8 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 – Device to measure visible light parameters Fluxamount of light Intensitybrightness 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 E v1 and E v2
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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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