optical principles: led fundamentals
DESCRIPTION
When light encounters a surface, or travels from one media to another, several interactions are possible. For general lighting, we are typically interested in reflection, transmission, refraction, total internal reflection (which is really a special case of refraction), and absorption.TRANSCRIPT
LED Fundamentals
Optical PrinciplesOptical Principles
08-04-201108 04 2011
Interaction of Light and Surfaces
Reflection
Specular Semi-Specular Diffuse
TransmissionDirect Semi diffuse Diffuse
Refraction
Transparent TranslucentDiffuse
GlassAir
Total Internal R fl ti (TIR)
Water
Convex (Convergent) Plano-Concave (Divergent)
Reflection (TIR)
Absorption
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Absorption
Reflection
θi = θr θrθi θi
Specular Semi-specular or semi-diffuse
Diffuse
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Refraction
n sinθ = n sinθ Light bends toward the normal nisinθi = ntsinθtg
when going from low index to high index (low density to high
density).
ni
θiLight bends away from the
normal going from high index to low index.
nt
θt
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Total Internal Reflection (TIR) and Critical Angle
Critical Angle: sinθc = nt/ni
Acrylic: n = 1.493, θc = 42˚1 2Polycarbonate: n = 1.586, θc = 39˚
2
3nt
ni4
nt
ni
5
θi θr
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Total Internal Reflection (TIR) and Critical Angle
Lightguides• Lightguides• TIR optics
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Fresnel Losses• When light strikes an interface between two different materials, some light is lost
Reflected
reflected (even at normal incidence)
Air
Plastic
Transmitted
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Fresnel Losses
Fresnel Loss Through Flat Acrylic PlateFresnel Loss Through Flat Acrylic Plate
90.0%
100.0%
70.0%
80.0%
90.0%
50.0%
60.0%
Transmitted
Reflected
20.0%
30.0%
40.0%
0.0%
10.0%
0 10 20 30 40 50 60 70 80 90
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0 10 20 30 40 50 60 70 80 90
Incident Angle (deg)
Disclaimer
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i i ti f f OSRAM O t S i d t G bH' t i i foriginating from one of OSRAM Opto Semiconductor GmbH's partners, or in view of products being a combination of an OSRAM Opto Semiconductor GmbH's product and a product of one of OSRAM Opto Semiconductor GmbH's partners. Furthermore, OSRAM Opto Semiconductors GmbH cannot be made liable for any damage that occurs in p y gconnection with the use of a product of one of OSRAM Opto Semiconductor GmbH's partners, or with the use of a combination of an OSRAM Opto Semiconductor GmbH's product and a product of one of OSRAM Opto Semiconductor GmbH's partners.
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