signage usports

LED Sign Module Technology

Bob Ponzini

Bob Ponzini is a channel development manager for OSRAM. He can be reached at Bob.ponzini@osram.com

LED sign module technology has evolved significantly over the years, both in performance and design. Manufacturers have introduced innovative evolutionary improvements that have resulted in a truly better mousetrap when compared to LED modules that were available several years ago. What are some of these more recent changes, additions, improvements, and features? Let’s start by looking at the mechanical design features made to aid with installation and identification.

 

Mechanical Design Features

Channel letter modules regularly have both a screw hole for mechanical connection and peel-and-stick high-bond double-sided foam tape feature. The reliability of the double-sided foam tapes have improved over the years, but is still often not recommended as the only means of fastening the module to the channel letter body. While the glue used in these tapes may be extremely strong and resistant to elemental changes, the substrates to which the tapes adhere can be suspect and inconsistently cleaned and prepared.

Thus, many manufacturers recommend or require that modules mount to channel letter backs using additional mechanical means of attachment. I’m sure there are sign makers who have experienced the frustration of trying to use the double-sided foam tape feature on the back of a module, only to find it difficult, time consuming, and tedious to peel off the release liner. Related complaints have been heard and now you’ll see some module manufacturers provide LED sign modules with an extra length of the release liner on the double-sided foam tape creating an effective tab to grab and peel, saving time and reducing frustration.

Mounting an LED sign module to the back of a channel letter or to the back of a single-sided cabinet sign using the provided screw hole is pretty straight forward. The hole can be just about anywhere on a small or short module. When you get into larger or longer modules, the location of the hole become more important. Longer modules really need the hole to be located near the middle of the module or may even require two holes, one on each end, in order to securely mount the module flat to its mounting surface.

Mounting of LED sign modules made specifically for double-face cabinets can be a little trickier. A variety of designs have surfaced that minimize use of tools and tedious hand labor to install double-face sign modules. These include:

  • LED sticks made in lengths equivalent to a fluorescent HO lamp and that retrofit into existing fluorescent sockets
  • Lattice-style of LED modules that can be hung from the top of a cabinet
  • LED modules with tool-less click and play mounting accessories.

Each has its own unique benefits, and they all are designed to minimize installation time and labor required for installing LED modules in cabinet signs.

  

Other Design Features

Protection of an enclosure against ingress of dirt or water, according to the International Electrotechnical Commission codes, is defined in IEC 529. LED sign modules designed for outdoor or potentially wet locations often have IP (Ingress Protection) code ratings of IP 66, IP 67, or IP 68. The first digit in these examples being a “6” means the enclosure is dust proof. The second digit deals with water ingress where a “6” means limited ingress from high pressure hose down, a “7” means handles temporary underwater immersion up to one meter deep, and an “8” means permanent high pressure immersion. Either IP 66, IP 67, or IP 68 are generally good for a vast majority of outdoor wet location environments and are readily available.

Internal thermal management, or the ability of the design of the sign module to remove heat from the discrete LED chip, helps keep the LED cool, aiding in life performance and/or allowing for higher ambient temperature applications of the sign module.

Material selections are also important in product design. For example, heat and/or UV light from the sun can degrade materials causing them to change color and possibly accelerate LED module color shift and lumen depreciation over time. The choice of UV stable materials is, therefore, and important part of the development process in quality sign modules.

 

LED Module Identification

Similar models of sign modules from one manufacturer can be sometimes easy to mix up. As a result, module manufacturers include written descriptors on the face or side of the module body. These descriptors may include markings indicating some of the following:

  • Brand
  • Part Description
  • Wattage
  • Color Temperature
  • Color
  • Voltage
  • Binning Codes
  • Production Date Codes, Etc.

Additionally, to quickly identify a monochrome colored LED module, the module itself may incorporate some color marking feature such as those shown in the example photos below.

 

Improvements to Discrete LEDs

The individual discrete LEDs used inside sign modules have continued to improve as well. That’s not to say that all LEDs are good because there are major differences. Some of the attributes that should be considered when engineers are choosing the right LED for sign modules include things such as:

  • Thermal Resistance
  • Efficacy (lumens per watt)
  • Color Over Angle
  • Color Consistency (from tighter binning)
  • LED Durability and Lifespan
  • Lumen Maintenance.

As the efficacy of LEDs improve, the wattage is reduced for like lumen packages. Decreasing the wattage can improve energy efficiency and payback. It also reduces the thermal load in the sign module which will provide more stable performance over life.  

 

Electrical Designs

LED boards, modules, or light engines are generally either a constant voltage or constant current design.

Constant voltage designs require a specific input voltage to the module from its power source. Although constant voltage designs tend to be inherently a little less efficient, they have the advantage of only being limited to the voltage drop across a long length of multiple modules in a chain and the loading of the power supply. Thus, one can run varying lengths of multi-module chains of sign modules, ideal for a sign maker cutting off ever varying module counts for different channel letters or cabinets. In constant voltage designs, a sign module with good design circuitry within the module converts the constant voltage to constant current at the LED level and includes current regulation circuitry in the module that yields consistent brightness from each of the modules operating on a power supply, regardless of whether there are only a few or there are many modules on that power supply.

The designs that are truly constant current designs may be a bit more efficient, but there are significant limitations and restrictions on the quantity of modules one can operate on a constant current power supply and still have consistent brightness between the groupings of modules in a cabinet or channel letter.

 

Improved Sign Module Optics

It is arguable to say that the design features having the biggest recent impact on LED acceptance and performance in channel letters and cabinets has been related to optics. Early module designs had no optical beam shaping lens over the LEDs. The output of the LEDs was most commonly a 120° Lambertian distribution. Those designs still exist and still work well, particularly in large deep channel letters. However, when used in shallow channel letters or cabinets, the distribution of light often results in non-uniform luminance on the sign face.

This effect can be minimized by using lower-lumen modules mounted closer together. but while that solution helps with luminance uniformity, it also increases material costs and installation labor.

Many sign modules today are available with wide-beam optics that spread the light in a “batwing” distribution pattern, named for the cross section shape of the light emanating from the module optics. Wide batwing optics allow for an improvement in luminance uniformity while keeping the LED modules spaced relatively far apart, particularly in shallow depth letters or in cabinets.

Most modules with optics spread the light in a 155° to 170° beam angle. Going beyond 170° doesn’t really make sense as too much light ends up hitting the inside walls of the letter or cabinet, never reaching the sign face.

The most recent advances in optical design have improved light distribution even further. Optics have evolved and can now square off a beam pattern when viewed face-on. Due to their quadrant-symmetric light distribution, square lensed sign modules can be placed optimally to achieve uninterrupted illumination.

In simple terms, it’s much more efficient to mate together adjacent square pools of light than adjacent round pools of light to achieve uniform illuminance. Square lens pattern designs have improved sign face uniformity even further in small/shallow cabinets and in channel letters ranging from six inches deep down to depths as thin as two inches or even shallower. 

 

Summary

LED sign module technology, performance, and design has evolved over the years since they were first introduced. Improvements in installation design features, LED performance, materials, durability, and optics make LED sign modules more attractive and compelling than ever.