Optoelectronics Chapter 1 Terminology

EM Spectrum

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

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

Photons E = h f Where h = Planck’s constant = 6.63 x 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

Radiometric and Photometric Terms

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

CIE Curve

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

Photometer – Device to measure visible light parameters Fluxamount of light Intensitybrightness Incidance

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

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