LEDs

LED Insights: Turning the Page on LED Technology

J. Bryan Vincent is an expert in the field of solid state lighting and electronic materials. He has dedicated the past 10 years to developing LED solutions specific to the sign industry and is a partner at Principal LED. He has a bachelor’s degree in Chemistry and a Ph.D. in Chemistry/Materials Science.

Previously I wrote an article on LED technology (“Turning the Page on LED Technology,” SDG, Aug. 2013) that focused on processing and substrate improvement. In this article, I will review some additional technology developments and the impact it could have on the sign industry.

Today, almost all of the current LED research and development is focused on the general lighting market for LEDs. General Electric, one of the biggest players in the traditional lighting market, has estimated that LED will account for about 70 percent of a $100 billion lighting market by 2020, compared with 18 percent in 2012. Since the sign industry will represent only a small fraction of general lighting (less than 0.5%), development will likely come in the form of adopting general lighting components and products to work in our industry.

Wafer sizeThis is nothing new. In the early 2000s, sign manufacturers began incorporating 5mm, piranha and other through-hole lamps that were developed in the signal and indicator industry to replace neon in channel letters. As a market developed for LEDs in automotive and niche linear lighting (with the development of the SMD device), sign makers began incorporating those lamps into larger signs requiring higher brightness. Over the past five years, as prices have dropped, LEDs found their way into backlighting for TVs and again LED providers to the sign industry have adopted those materials to make LEDs the dominating technology for backlit signage modules. So it is important to understand what is available, what is coming, and how we can use it.

Advanced Optics

As of late, the focus has been on industrial LED fixtures as the consumer lighting market develops and costs continue to come down. These fixtures require two things:

·         Lower cost mid-to-large chips that can put out a lot of lumens in a single package.

·         LEDs that are stable at higher temperatures due to the high amount of current in a smaller and smaller area.

We have begun to see these mid-output chips make their way into the sign industry. The problem with these materials is that there is too much light in a small area. In order to deal with this, many LED providers like GE, Sylvania and others have developed specialized optics to try and distribute the light laterally in order to evenly illuminate a sign.

The spiel to the sign maker is that for large signs, you need fewer modules, reducing labor costs, and they work better in thinner sign formats. I anticipate that optics will be used more and more commonly in sign modules over the next few years, as LED providers continue to adapt higher output LEDs to the sign industry. The counter argument to this approach is that the lighting pushes so much light laterally, that you don’t take full advantage of the LED efficiency. In addition, in smaller signs (less than 36” high), the costs of these optics begin to outweigh the labor benefits. Regardless, this has proven to be a viable and cost effective solution for large-format, single- and double-sided signage.

So what is next? We know that the LED makers are focused on the consumer market that will represent over 35% of the LED production long term. First, manufacturers will likely grab the lowest hanging fruit, which is the incandescent and CFL bulb market. Unfortunately the major problems (again) are focused around getting a lot of light into a small area, which doesn’t really provide significant benefit to the need for distributed lighting (like signs). However, there are some areas of research that could be beneficial.

AC Powered LEDs

The first is the development of what are called “AC LEDs.” Seoul Semiconductor (SSC) and others have an AC powered LED for replacing incandescent downlights up to 60W. LEDs are low voltage DC driven components (usually with a forward voltage of around 3V DC). AC LEDs work by putting around 30 chips in series, where the voltage adds together, resulting in a forward voltage of around 90V and a dropping resistor to set the current. The advantage to this type of system is that no driver is required other than an in-line or onboard rectifier to convert the AC to DC voltage. Seoul actually sells a module with an on-board IC that as the AC cycle advances its phase, the IC turns on more strings on the module. Think of it as an “automatic transmission.” Since only the fewest number of strings needed are on at any moment, efficiency is high; and because the particular LEDs used are manufactured by Seoul Semiconductor in very high volumes, system-level cost is relatively low.

What this could mean to the sign industry is the availability of LED systems that do not require an external power supply and could be wired directly into 110V AC. The primary barrier to entry will be ensuring safety of operation and installation, along with the appropriate regulatory certifications. This could be of major benefit to our industry from a cost standpoint, as well as reduction of installation times and removal of a separate failure point in the LED driver.

Replacing Fluorescents

The second area of advancement will occur as LEDs move to displace linear fluorescents in the general lighting market. This development has more applicability to the sign industry since fluorescents are a major component in commercial sign cabinets. The problem being solved is also one of more distributed and multi-directional lighting, which is in line with sign maker’s needs. How this problem will be solved is more of a scalability issue.

As LED chip manufacturers make bigger wafers in a single batch, they will be able to produce more chips for almost the same fixed cost. For example, if you can grow a 1” wafer in a single step and produce 2,000 LED die, going to a 2” wafer allows you to produce 8,000 die of the same size with the same number of steps. Figure 3 shows the growth of LED wafer size over time. These processing improvements have been and will continue to be a major force in reducing LED die costs over the next five years. This means that you can make and sell more smaller LEDs and distribute them across a substrate at a lower cost. As the costs of low output LEDs continues to fall, LEDs will move closer and closer in line with the cost of fluorescent lamps.

Early developments of fluorescent replacement products are already available. Sylvania currently sells an LED cabinet system that takes advantage of advanced optics (described earlier) to spread the light over the sign face and features an easy to use snap track system. The modules use high brightness LEDs requiring only 6 LEDs on each side of the module that can easily cover 1 square foot of illuminated surface. Principal LED has taken the approach of using a high number of lower output LEDs distributed in a 360 degree pattern across an extrusion that fits directly into T-12 sockets. Each Qwik Stik contains around 70 LEDs per linear foot. Sloan LED’s Sign Box II system uses nine mid-output LEDs per side in a roll out ladder format with easy to use brackets and clamps. All of these systems will evenly illuminate a sign face and are great examples of using different types of LED advancements (low, middle, and high brightness LED lamps) to achieve the same result.

The Take Home

The take-home message is to expect technology advances in the sign industry to come from multiple directions. Manufacturers will take different approaches based upon available materials to try and solve the same problem. Breakthroughs will likely come in the form of major production cost advancements and systems that shorten installation time or remove the need for additional materials and components.