By Dan Wett
Light-emitting diodes (LEDs) continue to gain popularity throughout the lighting industry, with different types available for different applications, including everything from sign letters and traffic lights to electronic indicators and Christmas lights. In all cases, they are coated silicon wafers that illuminate when excited with electricity.
The specific light wavelength emitted depends on the coating used on the wafer, in turn determining the visible colour. They are also covered with a lens cap to help spread out the light.
Over time, LEDs have become more cost-competitive with other forms of sign lighting. They are easy to install (usually with double-sided tape), they need very little maintenance and their energy efficiency can result in power savings of 50 per cent or more. Further, LEDs used in signs are typically 12-V systems that are far safer to use than traditional lighting.
While there are hundreds of LED systems available, it is important to source those specifically designed to light sign letters. These are low-voltage systems, approved by Underwriters Laboratories (UL), that are flexible enough to be installed inside sign letters and use lens caps with a wide viewing angle for shallow-can applications.
Another consideration is colour. The key is to match the LED’s colour wavelength to that of the plastic letter face. A red-faced letter is best lit with red LEDs, for example, and a green-faced letter is best lit with green LEDs. Colour consistency is also important; broadly available white LEDs range from 3,200-K (warm white) to 7,100-K (white).
One factor that can shorten an LED’s useful life is excess heat. Some systems need to be mounted onto a metal can to serve as a heat sink. So, if a sign will use plastic cans or backs, it is important to source LEDs that do not require this heat sink.
A good LED system should last at least five years, so it is important to source from a well-established, reputable manufacturer that will still be around by that time. Some systems are sold direct by the manufacturer, but most are instead available through sign supply distributors.
UL, which publishes electric sign safety standards, has tested and approved components for LED-illuminated letters. These carry a label indicating they are UL-recognized. Finished signs and sign sections produced by UL-approved shops, using these recognized components, can in turn be UL-listed.
Signs use modules comprising multiple LEDs. Strings of these modules can be spliced and sized to fit specific sign letters. There are two main types of LED-illuminated letters: face-lit and halo-lit.
Face-lit letters allow light to escape out of the front, i.e. through the plastic letter face. The cans or backs can be made of plastic or metal.
Low-voltage signs may not need to be UL-listed, however, so it is best to check with your local UL representative and electrical inspectors.
Halo-lit letters, on the other hand, allow the light to escape out the sides or back, thus creating a halo effect when the letters stand off from a wall. They are made with plastic or metal cans, with plastic backs to allow light emission.
Traditional sign letters required cans to be at least 127 mm (5 in.) deep, to allow sufficient space for their high-voltage neon lighting and wiring. LEDs with low profiles, however, have resulted in a shift in design, eliminating these traditionally deep cans and instead enabling sign letters to be as little as 51 mm (2 in.) deep.
When filling these shallow cans with LEDs for face-lit applications, it is important to space them properly throughout the letters to reduce shadows and hot spots. The required number of LED modules will vary based on the type of system, letter stroke and both LED and face colour.
Not all colours are equally bright; a green or blue sign may need more LEDs installed to achieve the desired effect. Many designers use white LEDs with translucent white faces, then cover them with translucent vinyl in the colour of their choice.