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=hf
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 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
• Intensity
• Incidance
amount of light
brightness
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