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LED FAQ
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Basic Concepts

What is LED?

LED stands for Light Emitting Diode, a kind of semiconductor which is used to transform electronic signal into visable light or infrared rays, by the characteristics of compound of semiconductor.


LED History


LED emerged in early 1960’s from the semiconductor light emitting theory. Red LED and yellow LED emerged in 1964, as well as blue and green LED came out in 1994. White LED was developed in 1996.

In recent years, with deeper research of semiconductor luminescent materials, LED manufacturing process has been improved greatly. New materials (nitrogen and phosphor crystals) were developed and applied in LED industry. Super bright LED with different color have been developed with light efficiency thousands times higher than before. In the history of lighting industry, High Brightness LED is one of the greatest inventions after Edison invented the incandescent bulbs.


LED Application


The inherent characteristics of LED, such as energy saving, long life, shock resistant, fast response, cold source, make it very suitable to be used as indicator, light, display, urban decorative lighting, etc. We can also find LED applications in our daily life everywhere: home appliances, telephones, the dashboard lighting, vehicles fog lights and traffic lights.

Keywords

Physical Parameter


● Pixel pitch

Distance between adjacent pixels’ center. 

● Density
The number of pixels in unit area. ( dot / ㎡ )
There is certain calculation between the number of pixels and the pixel pitch:
Density = 1 ÷ (pixel pitch)/m2

● The best viewing distance (for full clor LED display) 

Pixel Pitch(mm) Density(Dot/㎡) Best Viewing Distance (m)
Minimum Maximum
4 62500 5 13
6 27755 7.5 20
7.62 17200 9.5 26
8 15625 10 27
10 10000 12.5 34
12.5 6944 15.6 40
16 3906 20 54
20 2500 25 67
25 1600 30 80

The viewing distance depends on the size and pixel pitch of the display.
Of course, you can see the LED display even when you are not within the best viewing distance. The best viewing distance is for reference only.

Electronic Parameter


● Gray scale grade
Gray scale: For LED display, gray scale means the varying brightness grades between the highest brightness and the most darkness in one color.
Example: No gray scale grade, 8 grade, 16 grade, 32 grade, 64 grade, 128 grade, 256 grade and so on. More gray scale grade results more color, and the color can be more gorgeous. Instead, single color display only gives very simple change.

● Frame rate
The refreshing frequency of LED display information.
Example: 30Hz, 50Hz, 60Hz, 85Hz and so on. Higher refreshing frame frequency results the image changes better in continuity.

● Refresh rate
The times of LED display data repeat per second.
Example: 120Hz, 240Hz, 400Hz, 800Hz, 2000Hz and so on. Higher refresh frequency means stabler image display.


Optical Parameter


● Brightness of LED Display

Brightness of LED Display is the average brightness of the LED display in the normal direction, which means being perpendicular to the display surface. ( Unit: cd/㎡)
For the same pixel density, the brightness of LED display is depending on material, package and dimension of the LED chip. Bigger LED chip results display can achieve higher brightness.

● Viewing angle
Viewing angle is the angle between the two directions opposed to each other over the reference axis for which the luminous intensity is half that of the maximum luminous intensity. There are horizontal viewing angle and vertical viewing angel respectively.
To assume that there is a LED display with horizontal viewing angle 120 degree and vertical viewing angle 45 degree, the audiences will be able to see the best visual effect in this viewing angel range. Being outside this viewing angel range, which means we surpass this viewing angle range, the visual effect which audience can see will be less than normal brightness. Bigger viewing angle of the LED display results more audience and bigger area could be covered. The capsulation of LED chip determines the viewing angle of the LED display. The viewing angle of SMD LED lamp is better than oval LED. The viewing angle is inversely proportional to the brightness. 

● Viewing angle range (for full color LED display) 

LED Shape Horizontal Vertical
SMD LED 160° 160°
Oval LED 120° 60°
Round LED 60° 60°

Life span of LED display


LED (light emitting diode) is a kind of semiconductor components, and theoretically its life span is about 100,000 hours (in laboratory circumstance). The lifespan of LED display depends on the lifespan of LED Chip and lifespan of other electronic components. And MTBF (mean time between failures) is more than 10,000 hours.

Display Category

Factor LED Display Type Feature
Operating environment Indoor LED 
display
Applied in the indoor environment. Moderate   brightness, large viewing angel, close distance,   light weight, high density, suitable for watching in a close distance.
Outdoor LED 
display
Applied in the outdoor environment. High   brightness, high IP rating, waterproof,dust-proof   and UV-resistant, suitable for watching in a long   distance.
Color Single-color LED 
display
Monochromatic LED display is composed by single   color led lamp, it can display single color only,such as red, green, orange and so on.
Dual-color LED 
display
Dual-color LED Display is composed by red and   green LED lamp. 256 gray scale grade of Dual color   LED display can display 65,536 color. (Dual-color   LED display can display red, green and mix to   amber color)
Full-color LED 
display
Full color LED display is composed by red, green   and blue Led lamp. It can display 16,777,216 colors   or more.
Function Graphic LED display
( Asynchronous )
Designed for displaying off-line message such as   letter text and simple graphic.
Video LED display
( Synchronous )
Designed for displaying real-time, dynamic,   synchronous, various kinds of information, such as   2D or 3D animation, video, television, DVD and live   video broadcasting, etc.
LED lamp 
package format
Dot matrix LED
Dot matrix LED display is composed by LED chip   packaged in the plastic lattice within the LED   module, mainly applied in indoor single/dual color   LED sign.
SMD LED display
SMD 3-in-1 LED display is a new model in recent   years. LED chip is packaged in the transparent   plastic lattice with surface mounting technology. It   results smaller size, bigger viewing angle, and   lighter weight, which is especially for the indoor and semi-outdoor full color LED display.
DIP LED display

LED chip is packaged in a cup-type epoxy resin   frame enclosures. The high brightness makes it   suitable for outdoor purpose.

Comparison between LED display and other display equipment

LED display LCD display PDP plasma TV CRT cathode ray
Resolution Middle~High High High Middle
Brightness(cd/㎡) 80~10000 500 Above 680 140~500
Viewing angle 160° 140° 160° 170°
Response time 1μs ≥5ms 2~20μs Around 1μs
Power consumption higher low higher high
Acreage(inch) Freely splice ≤70(common) 40~100 ≤42(common)
Operating voltage(v) 2~5 2~5 100~250 (2~3)×104

Choose a Full Color LED Display (for commenrcial advertising)

Guides about choosing LED display

You need to consider a lot of factors before choosing LED display. The following are some guides for your reference.

STEP 1 Displaying function

For character text and simple graphic: select model without gray scale.

For example: Single-color LED display, Dual-color LED display.

For video and colorful graphic: select model with gray scale.

For example: Dual-color LED display, Full-color LED display.

STEP 2 Environments

For indoor purpose: Select indoor LED display. For example: Pixel pitch between 3mm and 10mm.

For outdoor purpose: Select outdoor LED display. For example: pixel pitch between 12.5mm and 38mm.

STEP 3 Viewing distance

For a close viewing distance: Select a LED display with smaller pixel pitch.
For a long viewing distance: Select a LED display with larger pixel pitch.

STEP 4 Display dimension

For displaying character: Select pixel pitch 16mm, 24mm, 32mm, 48mm and 64mm, according to the character quantity, and calculating the dimension.
For displaying video: Physical pixel density is more than 60,000 dots, according to the pixel quantity requirement, and calculating the dimension.


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