www.osram-os.com
CONFIDENTIAL
Optical Basics
Christine Rafael | Horst Varga | 6 June 2014 | Istanbul
Sarnikon
Agenda
• Luminance
– Definition
– Spot lighting
• Radiation characteristic
– fundamentals
• FWHM – full width at half maximum
• cumulated flux
• Fresnel reflections
– applications
• CRI
• Panel lighting
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
CONFIDENTIAL
CONFIDENTIAL
LED selection
Optical relevant project specifications
3
1. Brightness requirements
i.e. system luminous flux
1. Fv = 3000lm
= 25 • 120lm
= 75 • 40lm
2. Mechanical restrictions
i.e. size of luminaire
2. Size of LES is limited
 luminance requirement
OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
CONFIDENTIAL
Optical considerations
Luminance
Fundamentals
Luminous flux
per solid angle and per area
 Luminance as well as etentue are conserved
i.e. no increase of luminance or
decrease of etendue is possible
LV 
FV  lm 

A  m 2  sr 
Etendue
 Example: Spotlight
200lm and 12° opening angle, 50mm reflector
diameter
Luminance of spotlight
Area • solid angle
Et
 A    mm
2
 sr 
 n 2p sin 2   A
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
Lv,spot = 200lm/(25mm2 p)/0.07sr
= 1.45cd/mm2
CONFIDENTIAL
Optical considerations
High Power LED
 FV=200lm
 1x OSLON Square
– LED size 3x3mm²
 area: A=2.1²p = 14mm²
Low Power LED
 FV=200lm
 5x DURIS E5
– LED size 5.6x3mm²
 area: A=6.8²p = 145mm²
– Solid angle
FWHM 120° ≈ “lambertian” emission
=p
Y
X
Z
3D Layout
LCW CQAR.PC - Osram sample file
11/23/2011
OSRAM Opto Semiconductors GmbH
Confidential
– Solid angle, lambertian
emission of LED
=p
LCW_CQARpc_011211_sample_Zemax.ZMX
Configuration 1 of 1
 Luminance of source
Lv = 200/14/3.14 = 4.5cd/mm²
>> LV, spot
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
 Luminance of source
Lv = 200/145/3.14 = 0.44cd/mm²
<< LV, spot
CONFIDENTIAL
Light Intensity Distribution: What are the appl. limits?
Peak intensity
I
max


L

source
source
p *)
 Areflector
 Areflector
A
I < Imax:
source
*) for lambertian sources
– Reflector height restriction
– Light mixing
– special beam-shaping / spot smoothing
FWHM viewing angle
Relations
 Larger source luminance
 Larger peak intensity
 Smaller LES size
 Smaller FWHM viewing angle
Sources for intensive spots
 High lumen package
 Small light emitting area (LES)
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
The law of Etendue: the limiting relationship between
light source, reflector size and radiation angle!
CONFIDENTIAL
ELED  Esystem
LED
Light
φLED
Source
ALED
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
φsystem
System
Ap
CONFIDENTIAL
SOLERIQ
Optical considerations
How Source LES determines system CBCP
System example
 100mm reflector diameter
 12deg FWHM
 2000lm
In a given system, a smaller source LES delivers, higher CBCP
In narrow beam, spot applications Cd/W, not lm/W count
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
LED fundamentals
CONFIDENTIAL
Radiation characteristic
 definition of the LED emission normally by FWHM
(Full Width at Half Maximum) or luminous intensity plots
 c.f. datasheet:
radiation characteristic
100%
90%
80%
FWHM is just one
point in the
radiation
characteristic
normalised intensity
70%
60%
50%
40%
30%
20%
LCW CQAR.EC
10%
LCW CR7P.EC
LCW CRDP.EC
0%
-90
-60
-30
0
30
60
90
angle [°]
wide radiation characteristic most
suitable for reflector optics
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
narrow radiation characteristic most
suitable for secondary lenses
Optical fundamentals
Cumulated flux
CONFIDENTIAL
Optical Concepts

100%
90%
cumulated luminous flux
80%
70%
60%
50%
40%
30%
20%
LCW CQAR.EC
10%
LCW CR7P.EC
LCW CRDP.EC
0%
0
10
20
30
40
50
60
70
80
90
angle [°]
Reflector optics, high efficient when:
 most of emitted light hits reflector
 cumulated flux curve should increase
slowly
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
Lens optics, high efficient when:
 most of emitted light hits lens
 cumulated flux curve should increase
rapidly
Optical fundamentals
Fresnel equations
Definition
CONFIDENTIAL
Consequences, e.g. in streetlighting
The Fresnel equations describe the
behaviour of light when moving between
media of differing refractive indices. The
reflection of light that the equations predict is
known as Fresnel reflection.
(source: http://en.wikipedia.org/wiki/Fresnel_equations)
• angles obey Snell’s law
• Quantification
given by Fresnel
Equations
Fresnel reflections can lead to a
"destruction" of the bat wing shape of a light
distribution suitable for streetlighting
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
LED
CONFIDENTIAL
High power LED setup
Primary optics
Conversion layer
for generation of
white light
Chip
Substrate
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
LED
CONFIDENTIAL
Chiptechnology
Surface emitter
Emission only on top
side of the chip
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
Volume emitter
Emission on five sides of the chip
 wide radiation characteristic
LED radiation characteristic
CONFIDENTIAL
Radiation characteristic
Cumulated flux
100%
100%
relativer kumulierter Lichtstrom
relative Lichtstärke
Unusable light
50%
50%
Lambertsche Abstrahlung
Nicht-Lambertsche Abstrahlung
Lambertsche Abstrahlung
Nicht-Lambertsche Abstrahlung
0%
-90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90
Winkel [°]
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
0%
0
30
60
90
Winkel [°]
120
150
180
Application example 1
Single-LED
Light emitted at angles > 90° hits the PCB
 Losses at low PCB reflectivity
 With scattering PCB reflection use of light gets difficult
Reduced freedom of design
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
CONFIDENTIAL
Application example 2
TIR Optics
 TIR optics combine the properties of
lenses and reflectors and enable
compact optical solutions
 Light emitted at angles > 90° is
hardly usable
 Work around
 push LED „deeper“ into TIR lens
 shallow angles on buttom side of
lens required
 size and costs of lens
will increase
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
CONFIDENTIAL
Application example 3
LED cluster
CONFIDENTIAL
 Light emitted within full-width-at-halfmaximum is emitted without problems
 Depending on LED to LED distance
light hits the adjacent LED
 Refraction/Reflexion
 Scattering within the package
 High reflective packages can
minimise losses
3mm
4mm
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
 Light emitted at angles > 90° hits
- the adjacent LED package
- the solder interface
- the PCB
 usage difficult
Why do colors look different
under different lighting scenarios?
CONFIDENTIAL
You go into a shop and select a shirt
with your favorite colour …
… but at home you realize that the
colour of the shirt may look
different than in the shop!
WHY?
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
What is colour? … It’s all in the mind
Relative photoreceptor cell absorption
CONFIDENTIAL
Sensitivity of the human eye
Color
• Our brains’ interpretation of the response of the photoreceptive cells (rods and cones) in
our eyes to a defined band of electromagnetic radiation.
• ‘Colour’ only exists in our brains and is not a physical phenomena.
• Our brains will influence what we ‘see’ based on a variety of factors including experience.
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
The best colour illusion of all … WHITE light!
CONFIDENTIAL
Sunlight
RGB
BY
Flourescent lamp
All these spectral power distributions are perceived as ‘white’!
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
CONFIDENTIAL
The color rendering index Ra (1974)
Calculate the coordinates of the test color samples illuminated by
reference and test illuminant:
reference light source:
Black Body Radiator:
color temperatures in the
range of 2300K … < 5000K
Daylight Spectrum:
color temperatures in the
range of 5000K … 25000K
Test color samples:
R8
R7
R1
R2
R6
R3
R4
R5
R14
are calculated and stated separately.
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
CIE Publication 13.3 (1995)
R13
 Chromatic adaption: Von Kries adaptation
R9 transformation
R12
R11
R10
 Calculate the color differences in 1964 U*V*W* color space
colorrendering
samples indices
have been
but– are
not used for CRI Ra calculation.
The
8 +additional
6 special color
(Ri): defined,
Ri = 100
4,6Ei
(red) and
R13
(skin tone)
areRa
often
seen
R9General
Color
Rendering
Index:
= 1/8
 Rias significant for interior lighting and
CONFIDENTIAL
Conclusion on Color Rendering Index
 The existing CRI is a number that measures how good the test light source
reproduces the same colors like the reference light source
 There will always be a tradeoff between
– color fidelity, i.e. how good can you reproduce a color
– color preference, i.e. how much do you emphasize colors
– customized spectral power distribution for specific applications and
– efficacy
 Some applications, e.g. Street lighting,
do not need a high CRI at all!
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
LCW CRDP.CC datasheet
Frontpage of datasheet
CONFIDENTIAL
OSLON SSL
White versions overview
Sophisticated versions for every kind of
lighting requirement – in both 80° and 150°
Product
target
CCT range
Typ. CRI
LCW .CC
LCW .EC
LCW .PC
(color champ)
(eco champ)
(power champ)
Warm/neutral white
Warm/neutral white
Maximized light
quality
2700-4500K
95

LUW
Best compromise
CRI and flux
neutral white
Cool white
Maximized flux
Maximized flux
2400-5000K
4000 – 5700K
5700 – 6500K
82
70
various Indoor
Lighting, e.g. Office
Outdoor Lighting
Industrial Lighting
70
$$$
Applications
Premium Indoor
Lighting, e.g. Shop
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
Outdoor Lighting
Industrial Lighting
Office Panel lights
Simulation input
CONFIDENTIAL
Definitions
Top view
Side view
diffusor
h
PCB
d
LED pitch d symmetrical
in x and y direction
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
Homogeneity on diffusor plane
independent of diffusor performance.
When looking into the luminaire you will
see hot spots if there is no diffusor.
Office Panel lights
Illuminance plots
CONFIDENTIAL
20mm distance from PCB to diffusor plane
Large LED pitch
Small LED pitch
line of evaluation
• Most inhomogenious illumination is
diagonal line with respect to LED grid
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
• Total homogeneity is achieved if
LED pitch << PCB-diffusor distance
Office Panel lights
Illuminance line plots
CONFIDENTIAL
20mm distance from PCB to diffusor plane
Heading
• average illuminance on diffusor plane
• Peak-to-Valley deviation from average value
i.e. “visible” hot spots
• Evaluation
– Peak-to-Valley deviation
relative to average illuminance
i.e. (Max-Min)/Avg
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
Average
illuminance
Office Panel lights
Results
CONFIDENTIAL
Absolute scaling
Relative scaling
• 20mm distance PCB to diffusor plane
• Saturation effect below 20mm due to
numerical noise
• Approximately 23mm LED pitch suitable to
achieve homogeneity better than 20%
• Evaluation for different LEDs hardly differ
• Up to about 120% LED pitch with respect
to distance PCB to diffusor appear
suitable for homogenious illumination of
diffusor
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
Sarnikon
CONFIDENTIAL
Summary
• Luminance
– Definition
– Spot lighting
• Radiation characteristic
– FWHM & cumulated flux
– applications
• CRI
• Panel lighting
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OS SSL AE LC | Roland Schulz | Christine Rafael | Horst Varga
Sarnikon | 06-Jun-2014
