1. Lecture one

2. Displays classified by technologies  Cathode ray tubes (since 1900)  Flat panel displays (FPD) Emissive Plasma display panels (PDP) Vacuum fluorescent displays (VFD) Electroluminescent displays (ELD) Light emitting diodes (LED) Organic LED (OLED) Non-emissive (needs backlight or front light) Liquid crystal displays (LCD) E-ink, electrophoretic Electro-wetting MEMS (DLP, reflective grating)

3. Displays classified by driving techniques  Direct drive, simple multiplex Segment displays  Graphics displays (dot matrix) Passive matrix Active matrix, high resolution

4. Displays classified by viewing  Direct view  Projection  Head mounted displays  Holographic displays  3D displays

5. Early FPD market

6. FPD market now

7. Display market predictions

8. Hong Kong LCD market Glorious history: Hong Kong had 20% of world LCD market in 1996

9. Hong Kong companies  Major companies: Truly (732), JIC Nam Tai (Nasdaq), Yeebo (259) and Varitronix (710)  Truly 2006 turnover = US$580M  Varitronix 2006 turnover = US$148M  Nam Tai turnover = US$250M  Yeebo 2006 turnover = US$58M  Total ~1% of world market. Used to be 20%

10. Observation  Semiconductor IC market is about US$250B  Display market is about US$110B  Every university has a semiconductor IC program  Only a few universities have a comprehensive display program  The situation is changing. Many universities are trying to establish display programs

11. Displays: major subfields  Ultimate display: flexible, colorful, light weight, low power, 3D etc etc Ultimate displays Thin film transistors: materials, device physics Materials science, nanotechnology, manufacturing technology Display modes: LCD and OLED science and technology Video technology : drivers, signal processing, circuit design

12. Attributes of a good display  Low cost (capital cost and operating cost)  High brightness (>300 nit)  Large contrast ratio of at least 1024:1 (10 bit)  (cf: printed paper = 8:1)  Lots of gray scales (8 bit)  Large viewing angle (180 o ideally)  Excellent color saturation (100% NTSC color gamut)  Large size/weight ratio  Safe (no electrical hazard, radiation hazard)  Low/no power consumption  Flexible / rollable / foldable / durable

13. Common specs of LCD TV Resolution = 720p, 1080p Brightness = 500 nit 100% NTSC color gamut Contrast ratio = 10000:1 Display size = 42” (diagonal) Viewing angle = 170 o x 100 o What are these unit?

14. Display resolution - monitors  CGA (Color graphic array)320x240  VGA (video graphic array)640x480  SVGA800x600  XGA1024x768  WXGA1280x768  SXGA-1280x960  SXGA1280x1024  SXGA+1400x1050  UXGA (QVGA)1600x1200  QXGA2048x1536  QSXGA2560x2048 Pixel = square elements of the display matrix

16. Display resolution - TV PAL (Phase alternating by line)625 lines interlaced used in Hong Kong and Europe NTSC (National television system committee) used in USA525 lines interlaced HDTV : Format 1 (720p)1280x720 progressive Format 2 (1080p)1920x1080 progressive 2kx4k (newest)  TV is going from analog to digital.  Aspect ratio goes from 4:3 to 16:9.  TV and data terminals are (not) merging.

17. Moore’s Law for displays?  Moore’s law for semiconductors: number of transistors doubles every 18 months in IC  Moore’s law for displays? Total number of pixels ?  Improvement in quality such as viewing angle and color gamut may not be describable by Moore’s law  EGA  VGA  SVGA  XGA  SXGA  UXGA  QXGA  …  About 10x in 10 years, or 2x in 3 years Tiling

18. Ergonomics of resolution  Ultimately, we want a smooth display  Smoothness is related to sharpness of the human eye  Human eye has a resolving power of 0.15 mrad  Angle is measured in radian = size/distance  Typical viewing distance = 60cm. Therefore, a 1mm circle will sustain an angle of 1/600 rad or 1.67 mrad

19. Human vision  There are 120M rod cells and 6-7M cone cells. Rods are sensitive to light but not to colors - responsible for night vision. Rods are totally saturated in day vision  Cones are separated into RGB types and are responsible for normal vision and to provide high spatial resolution  Focal length of human eye (combining cornea and lens) is 17mm when relaxed. It is a fantastic design: Much reduced signal transmission bandwidth and signal processing capacity needed for the brain

20. Optics of the eye  170000 cells per mm 2 at center, corresponding to a spacing of about 2.5  m  Focal length of eye lens is 17mm. Thus resolution of the eye is thus 2.5/17000 or about 0.15 mrad and drops off rapidly to the sides  On the other hand, resolution of the eye lens is given by diffraction theory  Pupil = 3mm; thus a = 2.44 x 0.45 x 17 / 3 = 6.2  m  Resolution of human lens = a/2f = 0.18 mrad  The lens and the retina in the eye are perfectly matched – intelligent design!

21. Apparent size of an object is determined by the angle it sustains at the eye. Resolving power is given in terms of angle, not absolute size

22. Calculation of display resolution - monitor  If we want the display to be smooth, we want the pixel to be <60cm x 0.0002 rad = 0.12 mm  What is the pixel size for a 17” diagonal LCD monitor with SXGA resolution?  d = 17 x 25.4mm x 4 / 5 / 1280 = 0.27mm  This is 2.2x the requirement for smooth images  Equivalent to 25.4/0.27 dpi or 94 dpi  That is why UXGA or even higher resolution is needed for monitors  (Note dpi for printing has different meanings due to RGBY subpixels)

23. Calculation of display resolution - TV  If we want the display to be smooth, we want the pixel to be 2m x 0.0002 rad = 0.4 mm  What is the pixel size for a 40” diagonal LCD TV with 1080p resolution?  d = 0.4mm  Just right

24. Apple’s retinal display  i-Phone 3 (320x480)  i-Phone 4 (640x960) is called retinal display. It has a pixel density of 326 dpi or ppi (dots per inch or pixels per inch). It corresponds to a subpixel size of 78  mx26  m – requires very small transistors on the pixel in order to have reasonable aperture ratio  i-Phone 5 (640x1136) also has 326 dpi  Suppose we view the retinal display at 12” away, each pixel sustains 25.4mm/326/305mm=0.26mrad  Best human eye resolution is 0.15mrad  Not quite retinal!  Samsung S5 has 432 dpi (after subpixel rendering, thus not real). HTC One has 469 dpi also not a real pixel density

25. Viewing angle – solid angle Solid angle = angle sustained on a sphere where  = cone angle, unit = steradian (sr)  means entire half sphere  means entire sphere For FPD, the max viewing cone therefore is  Note analogy with a plane

26. Display optics - light  Light is electromagnetic waves, physically the same as radio waves, except that it can be seen  Waves = oscillating electric field and magnetic field  Intensity (brightness, Poynting vector) e.g. intensity of bright sunlight is 1000W/m 2.  Color (wavelength, frequency) Light is usually given in wavelength  (nm)  Polarization Direction of oscillation of electric field Ordinary light source is not polarized due to random orientation of many many many sources 3 important properties of light

27. Light  Light is a plane wave  Intensity ( I ), color ( ) and polarization ( E ) completely defines the wave W/m 2

28. Photometric units  LC TV brightness = 300 or 500 nit (what is nit?)  Radiometry – absolute units (W, W/m 2,…)  Photometry – units are related to human perception (lumens, nit, lux,…)  Wavelength (chrominance, color coordinate)  Intensity (luminance)

29. Photometry  Measurement of light as perceived by human  Brightness is measured in cd/m 2 (=nit)  Output of a light source is measured in lumens (lm)  Efficiency of light source is measured in lm/W  E.g. incandescent light bulb = 15 lm/W, fluorescent tube = 70 lm/W.  Best efficiency white light source - HID lamp: 100 lm/W  Goal for solid state lighting – 200 lm/W

30. Ocular response curve Photopic – bright environment (normal) Scotopic (night vision) K( ) Where does this conversion come from? Max = 673 lm/W at 550nm

31. Light sources  Common lighting : fluorescent tube and incandescent lamp (and the sun)  LCD backlight – CCFL and LED  Projectors – halogen lamps and arc lamps (HID and UHP)  Light source efficiency = watt to watt electrical efficiency x efficacy (related to spectral output)  Light sources are also characterized by a color temperature – equivalent blackbody  Ultimately all light sources will be LED – so they wish

32. Efficacy and efficiency  Given any light source (radiant flux) P( ) in W. The luminous flux F in lumens is given by  The luminous efficacy is defined as lumens per Watt  The luminous efficiency is defined as  normalized to the maximum of 673 lumens/Watt  Example: a fluorescent light tube has an efficacy of 70 lm/W or an efficiency of ~ 10%  For a light source, we have to take into account of electrical loss in terms of watt to watt efficiency:

33. Blackbody – actually it is not black BB is very fundamental in the study of light. It should be called thermal radiation – radiation in thermal equilibrium with an atomic system Planck’s law Stefan-Boltzman law a = 3.742 x 10 -16 W.m 2 b = 0.01438 m-K  = 5.68x10 -8 W/m 2 /K 4

34. Einstein’s rate equation  BB was explained by Einstein using the concept of spontaneous and stimulated radiation from an excited state  1905 – a year to remember : Einstein published 3 papers in Annalen der Physik: special relativity, photon quanta (almost invented the laser) and Brownian motion. In the photon quanta paper, he derived the Planck spectrum and explained the photoelectric effect  He got the Nobel prize on explaining the photoelectric effect

35. BB spectrum derived Spontaneous emission Photon induced absorption Photon induced emission (stimulated emission!) If the populations are at equilibrium with a photon bath  then d/dt=0 Thus (The population should be governed by Boltzmann statistics.) Therefore

36. BB efficacy Other non BB light sources can have higher efficacy Goal for SSL is 200 lm/W white light

37. How bright is 1 candle? – origin of lm/W  All of photometry is based on the brightness of a candle  The illuminance of a candle at 1 ft is defined as 1 fc or 1 lm/ft 2  The new candle with a luminous intensity of 1 cd is defined as 1/60 of the luminous intensity of 1 cm 2 of a 2046K blackbody  Using Stefan-Boltzmann law for blackbody emission, this is equivalent to 1.659W of radiation or an intensity of 1.659/  W/sr  Thus 1-cd = 1.659/  W/sr or 1 lm = 1.659/  W  Thus the conversion efficacy of 2046K BB is  1.659 lm/W or 1.82 lm/W  This agrees exactly with the calculated BB efficacy of 1.92 lm/W using the photopic curve. This confirms the lm/W conversion of the photopic curve  Example, if a certain flame has a temperature of 1550K, and has an area of 2 cm 2, then P = 65 W = 8.2 lm. Efficacy = 0.13 lm/W But not that bright This is a lot of power ! (mostly IR)

38. Conversion between photometric and radiometric units Total fluxAreal intensity Angular intensity Specific intensity (Brightness) RadiometryWW/m 2 W/srW/sr-m 2 PhotometryLumen (lm) lumen/m 2 (lux) lumen/sr (candela, cd) cd/m 2 (nit)

39. Illuminance and luminance  Define the illuminance by a candle at 1 foot away as 1 foot-candle and is defined to be 1 lm/ft 2  1 foot-candle = 1 fc = 1 lumen/ft 2 of illuminance  Thus 1 candle generates 4  lumens of light output (How many Watts of total radiation does a candle emit?)  Lambertian reflector (scatterer) Luminance Illuminance

40. Luminance of a flat light source  Same formula  P = Lumens of light emitted  A = area of light source   = emission solid angle  If the emission is Lambertian,   Sometimes the emission angular distribution is non-Lambertian, e.g. microcavity OLED

41. Why  ? Interpretation: Total emission solid angle is , even though the half space has a cone solid angle of 2 . Brightness (luminance) = lumen output from the light source / illuminated area / 

42. English system  Brightness is in foot-Lambert (fL)  Illuminance is in foot-candle (fc)  1 fc = 1 lm/ft 2 = 10.76 lm/m 2 = 10.76 lux  1 fL is defined as the luminance of a Lambertian surface upon illumination by 1 fc  Thus 1 fL = 1 fc/  sr = 10.76/  lux/sr = 3.426 nit

43. Vision ergonomics  Best reading brightness is 50-150 nit  CRT TV ~ 300 nit  LC TV (large size) ~ 500 nit  Light box for viewing x-ray ~ 1700 nit  Backlight unit for LC TV ~ 7000 nit  Bright sunlight on snow Illuminance = 1000 W/m 2 = 920000 lux Luminance = 920000/  = 290000 nit can cause snow blindness  Typical sunlight is perhaps 3000 nit. Thus sunlight readability of display is an important issue.  Moonlight ~ 10 nit  Thus natural light has huge dynamic range – can affect human behavior and mood – psychophysical

44. Example: photometry of a desk lamp  30W lamp at 0.5m away  Light output = 30x15 lm = 450 lm  Suppose said lamp concentrates light into a cone of 90 0, thus illuminated area =  (0.5m) 2 = 0.78m 2  Brightness = lumen / area /   Hence brightness = 450/0.78/  = 180 nit, perfect for reading 0.5m

45. LCD monitor : backlight analysis  LCD consists of backlight + LCD panel  Backlight of LCD monitor ~ 12W CCFL  Light output = 12x70 lm = 840 lm  17” monitor has an area of 10.2”x13.6” = 0.09m 2  Formula : Brightness = lumen / area /   Hence brightness of LCD backlight = 840/0.09/  = 2972 nit  Transmission of active matrix LCD panel = 7%  Hence LCD monitor will have a brightness of 2972x0.07 = 200 nit, just right  For TV need higher brightness of 500 nit due to larger viewing distance

46. LED BLU for cell phone  Backlighting unit for mobile phone LCD consists of several LEDs mounted on the edge of a piece of plastic waveguide. Structures on the plastic deflect light to the surface of the plastic to illuminate the LCD.  Suppose 2 LEDs are used with a total power of 10mW to illuminate an area of 6cm 2. Suppose that the efficacy is 35 lm/W. Assume further that the packaging and optical efficiency of the backlight is 60%. What is the brightness of this backlight?  Now assumes that the LCD transmits only 20% of the backlight (a CSTN display), what is the brightness of the final display? (70nit)

47. Projector brightness analysis  Typical projector uses a 120W UHP arc lamp with an efficiency of 70 lm/W  Thus available light is 8400 lm  Suppose one can use F/2 optics and collect 50% of the light onto the DLP panel, that is 4200 lm  DLP has color wheel for time sequential color- loss of 1/3 of light  Thus output ~ 1400 lm (check newspaper advertisement)  Suppose we want the luminance of the screen to be 500 nit, this output can only project an image of size 0.89 m 2  If we turn off the room light and allow a luminance of 200 nit, then the screen can be 2.23 m 2

48. Full color (16 million colors)  Each pixel is divided into 3 sub-pixels (RGB)  8 bit grey scale for each sub-pixel  Thus each color has 2 8 or 256 grey levels  Hence total possible colors = 24 bit = 2 8 x 2 8 x2 8 = 16,777,216

49. Color temperature  BB spectrum is universal  Every light source (display) gives a spectrum  Fit the spectrum with a BB curve – the corresponding temperature is called the color temperature  Sun has a color temperature of 5500K  Displays are characterized by a color temperature as well  Different cultures prefer different color temperature for displays. Japanese prefers 10000K, US and Europe prefer 6000K

50. Color science  Red – 650nm  Green – 550nm  Blue – 450nm  R( ), G( ), B( ) are the response curves of the three types of cones in the human eye  Any light is characterized by a spectrum L( ) (radiometry). Its perceived color is given by the tristimulus values R, G, B. We can normalize them by requiring R+G+B=1. Thus only 2 variables are needed to specify chromaticity

51. RGB - XYZ x( ), y( ) z( ) are called color matching functions

52. Color coordinate (CIE chart)  Need only two values to define color (chrominance values) White light = (0.33, 0.33) Edge of chart = pure color

53. Color mixing  All colors can be generated by mixing RGB – additive color mixing  R+G=yellow; G+B=cyan; B+R=magenta  Subtractive color mixing is used in paints  Color display – each pixel is divided into three sub- pixels (spatial color, as in printing)  Possible to use temporal color as well  Color gamut = triangle formed by RGB points  Color saturation = percentage of NTSC standard color

54. Color saturation  NTSC standard  Saturation of a particular color = distance from white point / edge of CIE chart (pure color)  Color saturation of a full color display = ratio of area of color gamut / NTSC  Notebook – 60% NTSC (thin color filter is used for saving power)  LCTV with CCFL – 80% NTSC  LCTV with LED backlight – 100% NTSC  LCTV with LED backlight and quantum dots color conversion – 110% NTSC

55. White light  White light can be obtained by an infinite number of combinations of RGB  Some are good for light (same as sunlight), some are not so good – measured by color rendition index  Solid state lighting applications – to replace lamps  Approaches : R+G+B, B+Y, R+C  (yellow=R+G, magenta=B+R, cyan=B+G)  Color coordinate = (0.33, 0.33)

56. Color rendition index  CRI is a measure of the quality of a light source in reproducing natural color  CRI is calculated by comparing with a perfect white light source at the same color temperature for eight standard colors

57. New development for color displays  Color mixing with 4 or 5 primary colors – better than 3 primary colors in color rendition  Time sequential color with LED backlight – this will be a major trend. Same pixel can be used for RGB  Advantages : better resolution, better light throughput, savings on color filters and processing  Disadvantage : need to switch backlight, need very fast LCD mode since sub-frame is <2ms only.