The LED's are surely the most important quality criteria when it comes to LED video displays. They determine the image quality of the display and are decisive in determining how the image quality is retained over time. The quality characteristics for LED's are very diverse, and, here too, the maxim applies: the most expensive choice is not always the best choice. To highlight an example from the automobile industry: You are sure to be able to spontaneously list a variety of luxury sedans, though you may not generally consider these when selecting a new vehicle. Price and purpose play major roles in the decision of which model to choose. And also, luxury sedans differ in many ways, although they often all meet the highest quality standards.
The quality of an LED is determined primarily by the chip used. It determines the service life of the LED and how the lighting behavior of the LED changes over time. The mayor Chip manufacturers of LED's are:
- Nichia (Japan)
- Cree (USA)
- AXT (USA)
- Epistar (Taiwan)
- Silan (China)
The prevailing opinion on the market today is that LED's made by Nichia are the best for use in LED video displays. However, they are also undeniably the most expensive LED's on the market by a wide margin. The price of LED's varies on average from less than one cent per LED to up to 15 cents and more, depending on the type of LED (RGB LED's with three chips in one housing are often more expensive). An extensive price difference can arise in manufacturing, depending on the LED's used.
The most important factor for purchasing a LED screen and determining which LED's to choose are:
- Brightness: The brightness of the LED's is measured in mcd (milli-candela). The higher the brightness, the better. You can run the display at a lower brightness, thus increasing the service life or increasing visibility during the day when the sun is shining.
- Electrostatic Discharge(ESD): The LED chips produced by various manufacturers differentiate themselves through a varying sensitivity to the effects of electrostatic discharge (for example due to contact). Display failures caused by electrostatic discharges can be prevented by implementing safeguarding measures against ESD in the production process. The following LED chips listed are indicating the voltages that the LED's can withstand in case of electrostatic discharges:
- Cree: 2000V
- Nichia: 1000V
- Taiwanese LED Chips: 800V
- Chinese LED Chips: 200~800V
- Sensitivity to Temperature Variations: Poor LED chips can fade faster, i.e. their service life can shorten, if they are exposed to high temperature variations. Depending on the country, temperatures can become extremely hot or cold during the summer or winter months, respectively. As a result, a poor LED quality could cause premature fading of the overall, expensive LED display.
- General Service Life: The general service life of the LED's often lies between 50,000 and 100,000 hours. (100,000 hours equates to 10 years of continuous display operation at full white, if no other factors exist which reduce the service life; such as increased heat in the display housing, or operating the LED's at overvoltage in order to balance brightness reduction.
- Brightness Reduction due Aging: Below is a table indicating the lighting reductions which arise within the first 10,000 hours: LED brightness reduction after the first 10,000 hours, sorted by manufacturer:
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Nichia (Japan)
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Cree (USA)
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AXT (USA)
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Silan (China)
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Epistar (Taiwan)
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Red LED
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2.5%
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Unknown
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Unknown
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Unknown
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28%
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Green LED
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2,50%
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26%
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8%
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7%
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28%
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Blue LED
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2,50%
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45%
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8%
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7%
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28%
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For the advertising screens we recommend always Silan LED’s, or the Cree LED’s which are a little more expensive than the Silan LED’s. Nichia LED’s, which are at least twice as expensive than Silan LED’s, for LED screens is mostly used for the professional industry like on stages or for television programs where quality is of high importance due to the high brightness and longer lifetime, and professionals invest a higher amount to have the screen performance and quality optimal at all times if not they are out of business and glamour is important in those industries. For advertising screens which are placed outside that quality is not necessary to be as optimal as the professional industry like stages or television programs because the screen is seen as an investment to shorten the ROI to less than 1 year and using the screen for advertising for over a period of at least 5 years to 8 years and gain 5 to 7 years from advertising.
If investing in Silan LED’s the initial investment is about 25%(Cree) to 50%(Nichia) lower than investing in Cree and Nichia LED’s. So for that Silan LED’s will have an ROI of around 1 year depending on the portfolio of clients that the screen owner has, the place where it is placed and price of the advertisements. When advertisers want to publish their products on the screen, of course quality is important but in practical terms the selling price of the commercial space on the screen will be the same if used Nichia or Silan or Cree LED’s because they don’t care about the lifetime and differences of brightness between Nichia, Silan or Cree LED's, they just want to be seen and promote their products and or services on the screen. What is important for the publicity clients is the resolution, if it doesn’t look pixelated they do see that as a plus and will attract more advertisers because the better the resolution the higher the impact of the advertisement and the higher the company’s goodwill of the product announced. Also for Nichia and Cree LED’s the ROI is one and a half to twice the time in comparison to Silan LED’s which is two years at least.
Normally Silan and Cree LED’s need 100,000 hours to reach around 40% of its total original brightness, Nichia will need 100,000 hours to reach 60% of its total original brightness. This is because the materials used are much more expensive for the Nichia LED’s than for the Cree and Silan LED’s and are better conductors. Besides Nichia uses around 50% of the energy used to burn the LED’s in comparison to the Silan and Cree LED’s. For example 1sqm of 16mm pixel pitch Silan and Cree LED’s consumes around 1200W/m2 and Nichia 575w/m2 which is less than 50% to get the same amount of brightness.
Many of the quality factors for LED's play a role in how they behave over time. Nichia LED's are the only ones for which it is generally known that they thoroughly meet the required criteria, positively setting themselves apart from other LED's on the market. The long-term values for some of the other manufacturers were not available. Many developments in the LED field are so new that long-term values over five, ten, or more years don't exist yet. If price and performance should be balanced, we recommend LED's with Silan chips. In terms of overall service life, Silan LED's are 1/3 weaker than Nichia LED's but they cost significantly less. With the service life of Silan LED's, you can run your display for 6 years of continuous operation at full white, although running the screen at full white is never done in reality. In displaying average video image content, the effective service life increases by two to four times as much, that is, 14 to 28 years, depending on the image content. In contrast to the still very expensive Cree LED's, Silan LED's age more evenly and also don't have as much lighting reduction after 10,000 hours. This proves particularly lucrative when exchanging individual pixel cards, since the calibration requirement is lower.
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