Basic LED technology presentation

1. February, 2004, page 1
Basic LED Technology

2. February, 2004, page 2
Working outside the video box
Imaging tools and techniques for today’s architects
Opener

3. February 2004, page 3
Barco
• Founded as the Belgian American Radio Corporation in
Belgium in 1934
• International company, headquartered in Kortrijk,
Belgium, with a global presence
• 4,135 employees worldwide; 550 in North America
• Barco Media USA headquartered in Logan, Utah
KORTRIJK

4. February 2004, page 4
Simulation &
Presentation
Barco
Vision
Barco
View
Company structure
Media
Events
Digital Cinema
Medical imaging
Avionics
Traffic Control
Defense & Security
Textiles
Plastics
Control
Rooms
Media &
Entertainment
Simulation
VAR
Edutainment
Presentation
Broadcast
Traffic
Surveillance
Sales
Markets
34% 19% 18% 13% 12%

5. February 2004, page 5
Barco View

6. February 2004, page 6
Barco Projection

7. February 2004, page 7
What is video?
Video is electronically capturing images and
sound and transferring them to an output
imaging device

8. February 2004, page 8
Lets talk about about the video viewer
• Perception is reality
• Emotion is based on what is
processed in the sub conscience from
the senses. Image and sound being
the dominant senses.
• Brightness and color perception are
different from person to person
• The perceived quality of video is
generally based on what is being
viewed presently
• The eyes and brain affect the way
video is received.
• Luminance, contrast and resolution
play a far greater role than color
• Great audio makes video look better
• A viewer tends to position himself
relative to a scene so that the
smallest detail of interest in the scene
eliminates raster or picture elements.
• Brightness of the area influences
flicker

9. February 2004, page 9
The Eye
• The innermost layer is the
retina –the light-sensing
portion of the eye. The
retina has retentive value
which means that it stores
images for a fraction of a
second It contains rod
cells, which are responsible
for vision in low light, and
cone cells, which are
responsible for color vision
and detail.

10. February 2004, page 10
The Eye cont.
•The color-responsive chemicals in
the cones are called cone pigments
and are very similar to the chemicals
in the rods.. There are three kinds of
color-sensitive pigments:
•Red-sensitive pigment
•Green-sensitive pigment
•Blue-sensitive pigment
•Each cone cell has one of these
pigments so that it is sensitive to that
color. The human eye can sense
almost any gradation of color when
red, green and blue are mixed.
•The eye can process about 100
shades of gray. Movie film can handle
about 50 and video about seven

11. February 2004, page 11
The brain
• If you divide a still image into a
collection of small colored dots, your
brain will reassemble the dots into a
meaningful image
• If you divide a moving scene into a
sequence of still pictures and show
the still images in rapid succession,
the brain will reassemble the still
images into a single movie (It takes
about 15 to 20 frames a second
before you begin to see smooth
animation) This is based on the
retention capability of the eye.

12. February 2004, page 12
Light Emitting Diodes
• Light Emitting Diodes (LEDs) are
plastic capsules containing a
specific chemical compound on a
microscopic wafer that emits light
when subjected to an electrical
current.
•Surface Mount Diodes (SMD) are
used by Barco on indoor products.
A surface mount diode may be
discrete or a 3-in-1 package.

13. February 2004, page 13
Light Emitting Diodes (cont.)
• Individual LEDs are available in many grades of
quality and shades of color. Barco uses high grade
red, green, blue and amber LEDs.
• When red, green and blue LEDs are clustered
together and shine at their full brightness, the
combined light emission appears white to the
human eye. Varying the intensity of the three
colors creates all the other shades.
• Amber LEDs are used for monochrome displays.

14. February 2004, page 14
Pixel
• A single cluster of LEDs is used as a pixel.
• A pixel is a picture element; the smallest individual
unit or piece of a video display image. A pixel is an
individual dot in a video display.
• Each pixel has its own color and brightness
attributes.

15. February 2004, page 15
Pixel (cont.)

16. February 2004, page 16
Pitch
• A display’s pitch is its measurement of distance
from the center of one pixel to the center of
another pixel.
• The pitch determines the viewing distance. The
smaller the pitch, the shorter the viewing distance.
Pitch
Pitch

17. February 2004, page 17
• Minimum Distance: The point at which the fully
illuminated red, green, and blue components appear to
the eye to blend into white.
• Maximum Distance: The point at which the smallest
characters the display can generate begin to be
illegible. This point varies greatly with the content of
the display.
• Minimum distance = 2’ x pitch
– Ex: 2’ x 12 mm = 24’
• Maximum distance = min. distance X 7
– Ex: 24’ x 7 = 168’
OR
• Maximum distance = 30 to 40 times
the height of the display
– Ex: 9’ x 12’ = 270’ – 360’
Viewing Distance

18. February 2004, page 18
Viewing Distance (cont.)

19. February 2004, page 19
Question
• What is the minimum
and maximum viewing
distance of a 3 mm
display?

20. February 2004, page 20
Matrix
• An array of pixels forms a matrix usually stated as
## x ## pixels.
• All Barco video and text boards are matrices.
• Scoreboards may be either a matrix or segmented
digits.

21. February 2004, page 21
Matrix (cont.)

22. February 2004, page 22
Fill Factor
• Fill factor refers to the amount of black space
between pixels.
• A high fill factor means more LEDs per ft² and
generally a smoother looking picture.
Low Fill Factor High Fill Factor

23. February 2004, page 23
Resolution
• Resolution is the total
number of pixels in a
display.
• The higher the number of
pixels the greater the
possible detail.
• A standard video signal
(NTSC) has a native
resolution of 645 x 485
pixels.
300x300
80 x 80

24. February 2004, page 24
Question
• Given a per pixel price of
$6.00, what is the cost
of an LED screen with
NTSC video resolution?

25. February 2004, page 25
Aspect Ratio
•Relationship in a video image between the
width of the image and the height of the
image expressed in generic terms of units
width by height (4:3, 16:9).
•The aspect ratio for NTSC video and most
computer monitors is 4:3. The standard
aspect ratio for digital HDTV is 16:9.

26. February 2004, page 26
Question
• What is the physical size
of a 10mm LED screen
with NTSC video
resolution?

27. February 2004, page 27
Viewing Angle
• The angle off center at which the display output
drops to half brightness. Expressed in degrees
horizontal and vertical.
– Ex: Horizontal 140° (±70°), and vertical 60º (±30°).

28. February 2004, page 28
Color Shift
•As the eye moves off-axis the brightness
reduction of the RG&B LEDs may not change
consistently.
•As the viewing angle increases LED’s begin to
shadow one another. The color shift should
happen after the viewing angle drop off.
•Vertical color shift may also be caused by the
shaders at extreme angles.

29. February 2004, page 29
Brightness
• LED brightness is measured
in candelas per square meter
(cd/m2) a.k.a. nits (roughly
0.3 foot lamberts). The
higher the number, the
brighter the display.
• No correlation with
illuminated brightness such
as LUX (Lumens per m²).
• 1500 nits provides readable
text in outdoor daylight.
Video requires up to 5,000
for good color depth.
• Indoor video requires 1,500
to 2,500 nits.
• Barco brightness measured at
6500ºK.

30. February 2004, page 30
Question
• What brightness would
you recommend for a
display facing the street
through a window?

31. February 2004, page 31
Color Temperature
• Measured in degrees
Kelvin, color temperature
is an indication of the
amount of “warmth”
(yellow, red tones) or
“coolness” (blue tones) in
a white light.
• Standard video color
temperature is 6500ºK.
• Barco’s color temperature
is adjustable.

32. February 2004, page 32
Contrast Ratio
• Contrast ratio is a measure of the dynamic range of a
displayed image - the distance between the “whitest”
white and the “blackest” black in a video wave form.
• There is no industry standard method of measuring
contrast ratio. LED has high numbers because it has no
residual glow when turned off in a dark room.
• A more important number for video is shades of gray.

33. February 2004, page 33
Calibration
• For even picture quality, the brightness of each
LED is calibrated (adjusted) to match the
brightness of the surrounding LEDs.
• Barco uses a combination of hardware and
software to automatically calibrate:
– Pixel-to-pixel
– Tile-to-tile

34. February 2004, page 34
HOW to choose a Daylight Display
Formula BasedFormula Based
update of valuesupdate of values
Color ValueColor Value
PassportPassport
Brightness PassportBrightness Passport
VIDEOVIDEO
PROCESSINGPROCESSING
• Measurement of individual LEDs
• Storage on EEPROM in Modules
• Individual color and brightness correction
• Update of the correcting value through time
• Uniform picture initially
• Uniform picture through time
• Lifetime color compatibility of module
with newer modules
EEPROMEEPROM
StorageStorage

35. February 2004, page 35
International Protection Rating
• International IP scale is a unique reference base for all
types of industrial applications.
• Tiles resistant to:
– Water
– Heat
– UV
– Vibrations
– Dust
– Salt
– Animal intrusion

36. February 2004, page 36
LED Lifetimes
0%
20%
40%
60%
80%
100%
120%
10000
20000
30000
40000
50000
60000
700
00
80000
90000
10000
Hours of Use
PercentageDegradation
Life Time Range
Life Expectancy
• Old LEDs never die, they just fade away.
• The life expectancy represents the time passed before
the LED fades to half brightness. LEDs fade at a
significantly faster rate after half brightness.
• Barco pixels range from 50,000 to 100,000 hours.