Power saving in LCD panels

Power saving in LCD panels How to save power while watching TV Hans van Mourik - Philips Consumer Lifestyle

May I introduce myself Hans van Mourik Display Specialist Philips Consumer Lifestyle Advanced Technology Lab. Palladium Photodesign ARTEMISIA Association Power saving in LCD panels - 2

Contents Introduction Power Consumption of Consumer Electronics Products Power Saving in LCD Panels Backlight Dimming Multi Primary Colour Conclusion ARTEMISIA Association Power saving in LCD panels - 3

Contents Introduction Power Consumption of Consumer Electronics Products TV power consumption European Community legislation LCD power consumption Possibilities for display energy consumption improvement Power Saving in LCD Panels Backlight Dimming Multi Primary Colour Conclusion ARTEMISIA Association Power saving in LCD panels - 4

About power consumption of CE products Electr(on)ical products in households consume twice as much power as 30 years ago. CE growth is main contributor. CE products account for 16% of the total domestic energy consumption, with televisions accounting for the biggest part (40%). It is predicted to become one of the largest domestic energy consuming sectors. Source: UK Energy Saving Trust, Rise of the Machines: A review of energy using products in the home from the 1970s to today, June 2006. ARTEMISIA Association Power saving in LCD panels - 5

Increased power consumption of TVs New display Technologies: Plasma, LCD, OLED Newer technologies tend to be more efficient, but this is more than offset by larger screens More TVs being shipped Increased TV watching (http://www.ofcom.org.uk/media/news/2009/12/nr_20091217) 3.5 hours in Europe 4.6 hours in the US Internet connected TVs increase usage ARTEMISIA Association Power saving in LCD panels - 6

Maximum allowed on-mode power [W] TV power legislation in the EC Annual electricity consumption related to televisions was estimated to be 60 TWh in 2007 in the European Community 24 Mt CO 2 emissions or 10 medium sized power plants Without measures increase to 132 TWh in the EC in 2020 European legislation forces power reduction EC regulation no 642/2009 of 22 July 2009 600 500 Full HD 2010-2012 All TVs 2012-400 300 200 100 0 40 60 80 100 120 140 160 Diagonal screen size [cm] ARTEMISIA Association Power saving in LCD panels - 7

Display power versus total power For living room TVs ( 80cm / 32 ) more than 85% of the consumed power is used for the LCD backlight Obviously we have to start power savings here 100% Display power vs total power 80% 60% 40% 20% 0% 40 60 80 100 120 140 160 Diagonal screen size [cm] ARTEMISIA Association Power saving in LCD panels - 8

Possibilities for display energy consumption improvement Backlight efficiency Lamp efficacy (Lumen / Watt) Backlight Dimming Brightness Enhancement Foils LCD efficiency Driving Circuitry Aperture ratio Multi-Primary Colour Alternative display technologies OLED The red items will be discussed in this presentation ARTEMISIA Association Power saving in LCD panels - 9

Contents Introduction Power Consumption of Consumer Electronics Products Power Saving in LCD Panels Backlight Dimming Concept Basic Algorithm 0D dimming 1D dimming 2D dimming 2D dimming per colour 2D dimming processing Power savings resulting from backlight dimming Multi Primary Colour Conclusion ARTEMISIA Association Power saving in LCD panels - 10

Backlight dimming concept Example: frog by night Dim pictures occur often in movies ARTEMISIA Association Power saving in LCD panels - 11

Backlight dimming concept Conventional system: backlight is fully on and LCD drive determines resulting picture + = Full White Backlight Dim LCD picture Resulting picture ARTEMISIA Association Power saving in LCD panels - 12

Backlight dimming concept Backlight dimming: both backlight drive and LCD drive determine resulting picture + = Dimmed Backlight Bright LCD picture Resulting picture Dimmed backlight requires less current Saves power! ARTEMISIA Association Power saving in LCD panels - 13

Basic implementation of backlight dimming Algorithm Determine the maximum video level of the whole picture Calculate the gain factor such that the maximum of the picture drives the display fully Reduce the backlight by the same factor Various methods are possible ARTEMISIA Association Power saving in LCD panels - 14

0D dimming No dimming All light sources have maximum luminance 0D dimming All light sources have equal, controlled luminance Dimming BL level & video gain depend on video frame content 0D dimming reduces power consumption Applicable to fluorescent lamps and edge lit LED ARTEMISIA Association Power saving in LCD panels - 15

1D dimming 0D dimming 1D dimming Luminance of each segment can be controlled individually Dimming BL level & video gain depend on local video content 1D dimming reduces power consumption (also compared to 0D dimming) Applicable to fluorescent lamps and edge lit LEDs ARTEMISIA Association Power saving in LCD panels - 16

2D dimming 1D dimming 2D dimming Luminance of each segment can be controlled individually Dimming BL level & video gain depend on local video content 2D dimming reduces power consumption (also compared to 1D dimming) Applicable to direct lit LED backlights (LEDs behind panel), especially for white LEDs ARTEMISIA Association Power saving in LCD panels - 17

2D dimming per colour 2D dimming 2D dimming per colour Luminance of each R, G and B can be controlled individually per segment Dimming BL level & video gain depend on local luminance and colour 2D colour dimming reduces power consumption (also compared to 2D dimming) For direct lit backlights, using R, G and B LEDs ARTEMISIA Association Power saving in LCD panels - 18

2D dimming example = + Resulting picture LCD picture Backlight ARTEMISIA Association Power saving in LCD panels - 19

3D versus 2D dimming Input picture 2D 3D Backlight drive Diffused Backlight ARTEMISIA Association Power saving in LCD panels - 20

2D dimming processing 1/2/3D dimming is more complex than 0D dimming First the backlight is calculated, than the diffused backlight and finally the video on a pixel by pixel basis. Video in Backlight value calculation 1st BACKLIGHT Light output calculation 2nd Panel image calculation 3rd PANEL Viewer ARTEMISIA Association Power saving in LCD panels - 21

Power consumption depending on # of segments Power saving has been simulated using a large number of DVDs For 2D dimming typically ~200 segments are used 60% power saving! ARTEMISIA Association Power saving in LCD panels - 22

Contents Introduction Power Consumption of Consumer Electronics Products Power Saving in LCD Panels Backlight Dimming Multi Primary Colour Brief Introduction to Colour Science HDTV gamut RGBW RGBY RGBYC RGBYCM Conclusion ARTEMISIA Association Power saving in LCD panels - 23

Power density [a.u.] Very brief introduction to colour science Physically a colour is defined by a spectrum: power density vs. wavelength 250 200 150 100 Tungsten Daylight 50 0 380 430 480 530 580 630 680 730 780 Wavelenght [nm] ARTEMISIA Association Power saving in LCD panels - 24

Tristimulus description of colour The human eye has three types of colour sensitive cones, so every colour can be described by 3 values, tristimulus e.g. Eye: LMS Long, Medium and Short wavelength cones Colour Science: XYZ Video: RGB Several different spectra result in the same colour perception and the same tristimulus values (metamerism) ARTEMISIA Association Power saving in LCD panels - 25

Calculation of colour coordinates XYZ are calculated as the integral of the product of the spectrum and the colour-matching functions: x-bar, y-bar and z-bar Y is the luminance From XYZ the luminance independent colour coordinates x and y can be calculated The x and y points form the CIE 1931 Chromaticity Diagram ARTEMISIA Association Power saving in LCD panels - 26

CIE 1931 chromaticity diagram y spectral locus 380 780 380 780 black body curve 380 780 x 380 780 line of purples ARTEMISIA Association Power saving in LCD panels - 27

MacAdam ellipses Shades of green are wide apart MacAdam ellipses show just noticeable differences. They illustrate that in this (x,y) diagram colour differences are not represented uniformly Shades of blue are close to each other (The elipses are all enlarged for clarity) ARTEMISIA Association Power saving in LCD panels - 28

CIE 1976 chromaticity diagram u = 4X/(X+15Y+3Z) v = 9Y/(X+15Y+3Z) or u = 4x/(-2x+12y+3) v = 9y/(-2x+12y+3) CIE 1976 Uniform Colour Space Chromaticity Diagram More uniform with respect to colour differences ARTEMISIA Association Power saving in LCD panels - 29

HDTV gamut area The blue line shows the colours in nature (Pointer s gamut) HDTV can render all colours within the white triangle However, the figure shows only 2 dimensions, while there is a 3 rd dimension, the Luminance (Y) ARTEMISIA Association Power saving in LCD panels - 30

Three dimensional HDTV gamut Colour scale indicates relative luminance (Y) dimension White = 1 Green ~ 0.7 Red ~ 0.2 Blue ~ 0.1 ARTEMISIA Association Power saving in LCD panels - 31

Multi Primary Colour R G B In an LCD the RGB colour filter transmits only about one third of the light (e.g. the red colour filter transmits red light, but blocks green and blue) The efficiency can be improved by using white sub-pixels (100% transmission) or secundairy colour sub-pixels (67% transmission) ARTEMISIA Association Power saving in LCD panels - 32

RGBW pixel High Brightness combined with High Colour Saturation rarely occurs in video it does not occur in natural scenes. Add a White subpixel to enhance the brightness of non saturated colours. RGB subpixels are reduced to 75% size, so saturated colours up to 75% brightness can still be shown unchanged. W=R+G+B = 75%, but the W sub-pixel is another 75% The overall peak brightness increases from 100% to 150% ARTEMISIA Association Power saving in LCD panels - 33

Luminance of RGBW panel Luminance of RGBW display (RGB display white is 1) Luminance of RGBW display relative to RGB display ARTEMISIA Association Power saving in LCD panels - 34

RGBW properties The brightness increase of white of 150% can be used to decrease the backlight power to ~70%. However, the RGB subpixels do shrink, and highly saturated bright colours (as in data graphics and animated movies) cannot be shown as bright and saturated as on an RGB display Especially yellow/gold colours (that can be bright in nature) suffer ARTEMISIA Association Power saving in LCD panels - 35

RGBY pixel The main problem in RGBW is the amplitude of yellow So, add a yellow sub-pixel rather than a white one. R G B R G B Y Keep the R and B subpixels relatively big to avoid too much loss in red and blue and to keep a good white Because green and yellow are close to each other in the chromaticity diagram they help each other and can be smaller White luminance is 120% of that of an RGB display ARTEMISIA Association Power saving in LCD panels - 36

Luminance of RGBY panel Luminance of RGBY display (RGB display white is 1) Luminance of RGBY display relative to RGB display ARTEMISIA Association Power saving in LCD panels - 37

RGBY properties R G B R G B Y Nice yellow, gold and blue colours Luminance of white of 120% can be used to reduce backlight power to ~85% Deficiency in red, green and cyan Especially deficiency in cyan noticeable ARTEMISIA Association Power saving in LCD panels - 38

RGBYC pixel Deficiency in RGBY mainly due to cyan Add a cyan sub-pixel R G B R G B Y C And optimize colour ratios White luminance is 122% of that of an RGB display ARTEMISIA Association Power saving in LCD panels - 39

Luminance of RGBYC panel Luminance of RGBYC display (RGB display white is 1) Luminance of RGBYC display relative to RGB display ARTEMISIA Association Power saving in LCD panels - 40

RGBYC properties R G B R G B Y C Nice gamut Luminance of white of 122% can be used to reduce backlight power to ~80% Deficiency only in green In practice acceptable ARTEMISIA Association Power saving in LCD panels - 41

RGBYCM pixel What about adding a magenta sub-pixel? R G B R G B Y C M And optimize colour ratios White luminance is 139% of that of an RGB display ARTEMISIA Association Power saving in LCD panels - 42

Luminance of RGBYCM panel Luminance of RGBYCM display (RGB display white is 1) Luminance of RGBYCM display relative to RGB display ARTEMISIA Association Power saving in LCD panels - 43

RGBYCM properties R G B R G B Y C M High luminance of white of 139% can be used to reduce backlight power to ~75% Deficiency in primary colours red, green and blue, but apart from that a good gamut coverage Not a high quality picture, but in this way a very efficient display can be built Better than RGBW ARTEMISIA Association Power saving in LCD panels - 44

Contents Introduction Power Consumption of Consumer Electronics Products Power Saving in LCD Panels Backlight Dimming Multi Primary Colour Conclusion ARTEMISIA Association Power saving in LCD panels - 45

Conclusions TV usage accounts for a relatively large part of the total power consumption Using backlight dimming up to 60% of the consumed power can be saved Using Multi Primary Colour up to ~ 30% power saving is possible, but it affects colour rendition. Some colours get better, but some others suffer, so further study is necessary ARTEMISIA Association Power saving in LCD panels - 46

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