Using LEDs in dimensional letters

by Matthew | 18 April 2012 10:23 am

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.

Sourcing systems
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.

Filling letters
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.

Halo-lit sign letters most commonly use white LED lighting, but other colours are also feasible. A variety of halo effects can be achieved, based on the number of LEDs and the standoff distance from the wall. A typical halo-lit letter projects about 38 mm (1.5 in.) off the wall.

The inside of the can should be painted white, to help maximize light output through reflection. Another consideration is the wall sheen. The halo effect works best when the wall has a semi-gloss or matte sheen. The use of a light-diffused plastic back or translucent vinyl will help spread out the halo effect.

Installation options
LED-illuminated letters can be either mounted directly onto a wall or mounted onto rails or raceways that allow them to project from a wall. The choice may depend on the following factors:

• The nature of the wall (i.e. whether it is flat or uneven).
• Local sign codes.
• Property-specific guidelines (e.g. if the sign is for a business within a shopping mall that specifies one option or the other).
• The electrical system (i.e. where and how the wiring will run).
• The size of the letters.
• The copy layout.

Traditional neon-lit channel letters have to be mounted onto large raceways to contain their high-voltage wiring. Low-voltage LED systems do not have the same requirements and may instead use small raceways or rails. These can be bought or built.

Direct mounting to a wall is another option. It can be handled in much the same way as with non-illuminated dimensional letters, but—as when using raceway and rail systems—a wiring and power supply installation plan will need to be developed with a licensed electrical contractor.

All power supply holes will need to be located and drilled through. The holes might need to be centred, for example, to correspond with a raceway. For a UL-listed exterior sign, 6.4-mm (0.25-in.) ‘weep’ holes are also required in all letter drops. Face holes will need to be drilled to allow the faces to be attached to the cans.

It is important to keep in mind that even though low-voltage LED-lit letters require little electrical infrastructure, they are still subject to the same sign code rules affecting higher-voltage illuminated signs. Installers should study and understand all applicable electrical and sign code requirements.

Dan Wett is a technical adviser and writer for Gemini Canada, which manufactures plastic and metal letters, logos and plaques for the sign industry. This article is based on a seminar he presented at the United States Sign Council (USSC) Sign World International show in December 2011. For more information, visit www.signletters.com[6] and www.ussc.org[7].

Source URL: https://www.signmedia.ca/using-leds-in-dimensional-letters/

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