Optoelectronics

Chapter 1Terminology

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

• 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

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

• Photometer– Device to measure visible light parameters• Flux amount of light• Intensity brightness• 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 Ev1 and Ev2

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