Displays and signs call for improvements in green and white LEDs
Speakers at a recent conference described trends and challenges in the full-color video display and signage markets.
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For sports stadia and events, full-color video displays showing replays and magnified views have become a requirement, if not a necessity. Even high schools in the US are starting to deploy these products, which are also a feature of music events, trade shows and many other locations requiring video shows with excellent color reproduction.
The industry has seen many outdoor "spectaculars"- very large screens containing millions of LEDs. "This is a growing market, and as chip costs continue to fall, the new screens are staying large," said van de Ven. Typical costs can exceed $5 million for high resolution screens measuring in excess of 200 m2.
Monoblocks, which are small screens measuring up to 120 inches (diagonal) are non-modular, unlike larger displays - essentially they are like large plasma screens. Clearchannel has deployed 85 such screens at street level outside subway stations in New York City; these have a brightness of 3000 nits and are wireless networked. Such screens can command 3-6 times the revenue of a backlit poster, justifying the higher cost, although return on investment still takes a few years.
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The biggest problem for full-color video screens is the need to dynamically adjust the signal to adjust for the variation in LED performance within bins. "Also, red, green and blue LEDs all degrade at different rates, and blue LEDs from the same bin also degrade differently," said van de Ven.
In terms of future development, reduced LED cost will help video screens to penetrate new markets, but this is not the biggest challenge, said van de Ven: "We have enough brightness, what we need now is reliability and uniformity."
Signage seeks cost reduction for white
According to Jim Sloan, president and CEO of SloanLED, the US market for LED-based signs is dominated by channel letters, which have an 84% share. This includes reverse channel letters, where LEDs are used to project light from the rear of the sign onto the building or other mounting surface, creating a halo effect around the letter. Border and perimeter lighting makes up a further 13% of the market.
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Other challenges for using LEDs in the sign market include selecting the correct spacing: generally there is a need for even light distribution without the appearance of spots of light, and this introduces a complex trade-off with the LED power and the system cost.
Sloan also highlighted the need for standardized systems (in terms of appearance, voltages etc), particularly across large projects, for example corporate identity signs on multiple retail outlets or gas stations. However, there are no standards in place: "Companies work in the hope that by winning large programs they will be able to establish standards that other suppliers follow," said Sloan.
Another LED challenge in this market is matching the LED colour to the lens, which is crucial in projects that portray a corporate image colour. The final challenge is to optimize the voltage, line loss and output consistency; customers generally want runs to be as long as possible, but the distance from the first LED to the power supply can vary considerably.
For the future, Sloan is looking towards standardization for the operating voltage of signs - possibly at 12V DC. Also, he predicts an increase in ruggedness and ease of use (including power optimization), and an increase in viewing angles together with optimized dispersion patterns.