Flat Panel Displays

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Flat Panel Displays

Prof. Shin-Tson Wu

College of Optics & Photonics University of Central Florida

http://lcd.creol.ucf.edu/

Email: swu@mail.ucf.edu Office: CREOL 280

Phone: 407-823-4763

OSE 6938P

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OSE 6938P Lecture 1

Color Science

& Engineering

Outlines:

1. Introduction 2. The Eye

3. Colorimetry

4. Light sources

5. Photometry

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Introduction

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Introduction: What is color?

•Radiometry– intensity, spectrum, polarization, phase…

•Colorimetry– red, blue, green…

•Photometry– brightness, reflectance, transmittance…

•Psychometry– warm, cold,

harmonic…

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Historic Review of Color Definition (1)

Famous Color Circles

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Historic Review of Color Definition (2)

Famous Color Circles

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Formation of Color (1)

1. Light Source Illumination-- Visible Range, Natural or Man-Made

2. Objective Interaction--

Absorption, Transmission, Reflection, Scattering, and Fluorescence

3. Produce Stimulus-- Photons 4. Receive Stimulus-- The Eye,

E-O Effect

5. Interpret Stimulus-- Brain

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Formation of Color (2)

Wavelength between 380nm to 780nm

Light

source Reflectance Eye’s

Responsivity Color

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Light Source (1)

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Light Source (2)

Color Rendering Index (CRI) and Color Temperature

6500K 10000K

5000K

X

Y

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Objective Interaction– Reflection (1)

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Objective Interaction– Reflection (2)

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Color Mixing

Additive Subtractive

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Produce and Reproduce a Color

Printing System

Display System

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Homework #1: Color Mixing

Questions:

1. Is color printing a kind of additive or subtractive mixing? Why?

Due 1/18/07

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The Eye

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Human Eye Structure

• Cones: Provide color sensitivity

• Rods: Color-insensitive

• Color perception depends on light level

• Scotopic vision regime: Low-light-level-vision regime

• Photopic vision regime: High-light-level-vision regime

Ref: http://www.pde.rpi.edu/courses/05s/led/ssl/frame.htm

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Cone and Rod-- Spatial Distribution

Cone: +/- 10^o

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Cone and Rod– Spectral Sensitivity

1923 Gibson and Tyndall 1945 Crawford

Cone: Bright (>1nit), color, 555 nm Rod: dark (<0.001 nit), gray, 510 nm

CIE (Commission

Internationale de l’Eclairage) 1924, 300 people, 2-3^o

1951, <30 yrs, >5^o

Cone

Rod

Relative Radiometric Intensity (log)

Wavelength (nm)

Rod Cone

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Spectral Sensitivity of Rods and RGB Cones

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CIE 1978 Eye Sensitivity Function and Luminous Efficacy

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• Visible range:

390 – 720 nm

• Definition of lumen: Green light (555 nm) with power 1 W of has luminous flux 683 lm

• Efficacy of

radiation gives number of

lumens per optical Watt

• With same output power, green light are brightest

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CIE Standards

There are several standards:

•

Photopic:

• CIE 1931

• CIE 1978

•

Scotopic:

• CIE 1951

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Visual Signal Transmission

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Video Compression

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Which circle is bigger?

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Parallel Lines?

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How many colors in this figure?

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Adaptation

Spatial Domain Visual Experience

Ref. M. A. Webster, Opt. & Photon. News 16, 19 (2004).

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Sharpness of the Eyesight

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Sharpness of the Eyesight

100 cd/m² 0.1 cd/m²

10 cd/m²

1 cd/m² 1000 cd/m²

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Colorimetry

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Colorimetry

Red

Orange Yellow

Greenish yellow Green

Bluish green Greenish blue

Blue Purple

Black

White

Value

Hue Chroma

•Hue (φ)– that quality of color which we describe by the words red,

yellow, green, blue, etc.

•Value (z)– that quality of color which we describe by the words

light, dark, etc., relating the color to a gray of similar lightness.

•Chroma (r)– that quality which

describes the extent to which a

color differs from a gray of the

same level.

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Color Matching

Black shadow

Eye Red

Green Blue

Light Black shadow

White screen

R

_Q

≣ - R’

_Q

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Color System

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J. C. Maxwell System

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J. Guild System

-- 630nm, 542nm and 460nm; 7 people; 2

^o

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W. D. Wright System

-- 650nm, 530nm and 460nm; 10 people; 2

^o

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CIE 1931 (R, G, B) System

-- 700nm, 546.1nm and 435.8nm

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CIE 1931 (X, Y, Z) System

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Color Matching Functions and Chromaticity

λ λ

λ

= ∫

_λ ^x

⁽ ⁾

^P

⁽ ⁾ ^d

X

λ λ

λ

= ∫

_λ ^y

⁽ ⁾

^P

⁽ ⁾ ^d

Y X, Y, and Z are tristimulus values

λ λ

λ

= ∫

_λ ^z

⁽ ⁾

^P

⁽ ⁾ ^d

Z

Chromaticity diagram and chromaticity coordinates x, y

x

=

X

+ Y + Z

y

=

Y

X

+ Y + Z

z chromaticity coordinate not needed, since x + y + z = 1 Uniform chromaticity coordinates u, v and u’, v’

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CIE 1931 Chromaticity Diagram

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Color Purity and Dominant Wavelength

Caution: Peak wavelength and dominant wavelength can be different. Peak wavelength is a quantity used in physics and

optics. Dominant wavelength is used by in human vision.

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Statistical Data

1. Trichromatic Color Matching

2. Different Age and People

3. Convergent Points

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MacAdam Ellipses

• Color differences cannot be discerned with in the MacAdam ellipses

• Axes of MacAdam ellipses are shown 10 times longer than they are

• Humans can discern about 50 000 different colors

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CIE 1976 LUV System – An UCS (Uniform Chromaticity- Scale) System

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3-D Color System

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Chromaticity of D65 illuminant with different Y

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Munsell Color System

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Munsell Color System (with Constant Hue)

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CIE 1976 LUV Color System

Constant Hue

Constant Lightness

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CIE 1976 LUV Color System

Constant Hue

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System Transformation

Colorimetry Formulas

Nonlinear behavior of Y

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Gamma Value

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Light Sources

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White Illuminant – the Solar Spectra

• Note: There are many ways to create white light

• Sunlight is not an efficient way to create white light. Why?

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Color Temperature

• Planckian spectrum or black-body radiation spectrum

• As temperature increases, objects sequentially glow in the red, orange, yellow, and white

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Color Gamut

• Color gamut

• Gamut of Red-Green-Blue light source has triangular shape

• Area of gamut matters for displays, color printers, etc.

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Example of color mixing

• RGB color mixing

• Color gamut

• Gamut size increases with the number of light sources

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Color Rendering

• A light source has color rendering capability

• This is the capability to render the true colors of an object

•

• Example: False color rendering

• What is the color of a yellow banana when illuminated with a red LED?

• What is the color of a green banana when illuminated with a yellow LED?

Î Î

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Example of Color Rendering

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• Clear differences in the color rendition can be seen in this August Renoir painting (left-hand side: high CRI; right-hand side: low CRI)

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Color Rendering Index

• The color rendering capability of a test light source is measured in terms of the color rendering index

• Color rendering index of a high-quality reference light source is CRI = 100

• An incandescent light source with the same color temperature serves as the reference light source

• Eight color sample objects serve as test objects

•

• Example:

Color sample under reference source

illumination

Color sample under test source

illumination

Î slight difference in color!

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Calculation of Color Rendering Index

• CIE color definition: Color = Brightness, hue, and saturation

• Color rendering index: CRI = 100 – Σ_{i = 1…8}∆E_i*

• ∆E_i* represents color change

• CRI is a very good metric – but not a perfect one!

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Reflectivity of Color Sample Objects

• Sample objects (Fruit, wood, etc.)

• 8 standard objects (Î General CRI)

• 6 additional objects (Î

Special CRIs)

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Discussions of Color rendering index (CRI)

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• The reference objects are illuminated with reference light source. As a result, object will have a certain color.

• The reference objects are then illuminated with test light source. As a result, object will have a certain, but different, color.

• The CRI is a measure of the sum of the differences in color.

• If color difference is zero, then CRI = 100

• If color difference is > zero, then CRI < 100

• Some applications require high and very high CRI. Examples?

• Some applications do not require a high CRI. Examples?

• For some applications, CRI is irrelevant. Examples?

• Caution: CRI depends on the selection of the reference light source.

Recommended for reference light source: Planckian radiator.

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CRI Examples

Light source Color rendering index

Sunlight 100 Quartz halogen W filament light 100

W filament incandescent light 100 Fluorescent light 60 – 85 Phosphor-based white LEDs 60 – 90 Trichromatic white light LEDs 60 – 90 Hg vapor light coated with phosphor 50

Na vapor light 40

Hg vapor light 20

Dichromatic white light LEDs 10 – 60 Green monochromatic light − 50

Table: Color rendering indices (CRI) of different light sources.

• CRI > 85 suitable for most (even most demanding) applications Ref: http://www.pde.rpi.edu/courses/05s/led/ssl/frame.htm

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Photometry

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Photometry vs Radiometry

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History of Photometric Units

• Photograph shows plumber’s candle

• A plumber’s candle emits a luminous intensity of 1 candela (cd). The cd is historical origin of all photometric units.

• First definition (now obsolete): The luminous intensity of a standardized candle is 1 cd.

• Second definition (now obsolete): 1 cm² of platinum (Pt) at 1042 K (temperature of solidification) has a luminous intensity of 20.17 cd.

• Third definition (current): A monochromatic light source emitting an optical power of (1/683) Watt at 555 nm into the solid angle of 1 steradian (sr) has a luminous intensity of 1 cd.

• Candlepower and candle are obsolete units. Candlepower and candle measure luminous intensity and are approximately equal to one cd.

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Luminous Flux, Illuminance, and Luminance

• luminous flux: A light source with a luminous intensity of 1 cd emits a luminous flux of 1 lm into a solid angle of one steradian

• An isotropic light source with a luminous intensity of 1 cd emits a total luminous flux of 4π lm = 12.56 lm

• Illuminance: If a 1 m² surface receives a luminous flux of 1 lm, then the illuminance of the surface is 1 lux

• Example: Moonlight 1 lux; reading light 10² – 10³ lux; surgery light 10⁴ lux; direct sunlight 10⁵ lux

•

• Luminance is the luminous intensity emitted per unit area of a light source. Luminance is a figure of merit for displays. Typical displays have a luminance of 100 – 500 cd/m².

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Luminous Flux and Efficiency

Luminous flux

^{(Unit: lm)}

∫

_λ

^λ ^λ ^λ

=

Φ ( ) ( ) d

W 683 lm

lum V P

Luminous efficacy

(Unit: lm / W)

( _∫ )

∫

_λ

^⎟ _⎠ ^⎞

_λ

^λ ^λ

⎜ ⎝

⎛ λ λ λ

= Φ

= ( ) ( ) d ( ) d

W 683 lm /

efficacy

Luminous

_lum P V P P

Luminous efficiency

(Unit: lm / W)

) ( / efficiency

Luminous = Φ

_lum IV

Caution: Some call “luminous efficacy” the “luminous efficacy of radiation”

Caution: Some call “luminous efficiency” the “luminous efficacy of the source”

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Conversion Factors of Different Units

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Homework #2: Color Science

1. The CIE 1931 coordinate of the white light source E is (0.33, 0.33). Please find the R:G:B luminance ratio (in terms of photometry) for such a light source. (Hint: The wavelengths for the R, G, and B prime lights are 700nm, 546.1nm and 435.8nm)

2. Find the R:G:B luminance ratio in terms of radiometry

R G B

l 700nm 546.1nm 435.8nm x 0.735 0.273 0.166 y 0.265 0.718 0.008

z 0 0.01 0.826

V(l) 0.0041 0.9841 0.018