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

All information contained in this document has been checked with the greatest care. OSRAM Opto Semiconductors GmbH can however, not be made liable for any damage that occurs in connection with the use of these contents.

OSRAM Opto Semiconductor GmbH makes no representations and warranties as to a possible interference with third parties' intellectual property rights in view of products

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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