Basic led technology

February, 2004, page 1

Basic LED Technology

February, 2004, page 2

Working outside the video box

Imaging tools and techniques for today’s architects and designers

Opener

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

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Simulation & Presentation

BarcoVision

BarcoView

Company structure

MediaEventsDigital Cinema

Medical imagingAvionicsTraffic ControlDefense & Security

TextilesPlastics

ControlRooms

Media & Entertainment

SimulationVAREdutainmentPresentation

BroadcastTraffic Surveillance

Sales

Markets

34% 19% 18% 13% 12%

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Barco View

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Barco Projection

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What is video?

Video is electronically capturing images and sound and transferring them to an output imaging device

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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

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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.

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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

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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.

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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.

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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.

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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.

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Pixel (cont.)

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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

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• 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

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Viewing Distance (cont.)

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Question

• What is the minimum and maximum viewing distance of a 3 mm display?

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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.

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Matrix (cont.)

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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

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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

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Question

• Given a per pixel price of $6.00, what is the cost of an LED screen with NTSC video resolution?

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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.

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Question

• What is the physical size of a 10mm LED screen with NTSC video resolution?

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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°).

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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.

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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.

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Question

• What brightness would you recommend for a display facing the street through a window?

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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.

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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.

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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

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HOW to choose a Daylight Display

Formula Based Formula Based update of valuesupdate of values

Color Value Color Value PassportPassportBrightness PassportBrightness Passport

VIDEO VIDEO 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

EEPROMEEPROMStorageStorage

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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

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LED Lifetimes

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Hours of Use

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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.