Illuminated letters
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Signage: From incandescent light bulbs to LED letters

© istockphoto/-visualspace

Advertising messages are in use around the clock. It is therefore hardly surprising that their illumination has become increasingly energy-efficient. However, this development also presents an increasing number of new challenges for the material being used.

The world has virtually been waiting for some inventions, one of them undoubtedly being the incandescent light bulb. Since Thomas Alva Edison applied for a patent for his design in 1880, the incandescent light bulb has revolutionized the lighting of living spaces and streets – and also advertising.

Attract attention!

Instead of the metal or wooden signs that had long been the norm, the incandescent light bulb created illuminated writing and shapes for the first time. In the “Golden Twenties”, they were already making the inner cities of the world’s first metropolises shine brightly. By the 1950s, the incandescent light bulbs in illuminated advertising had been largely replaced by the even brighter – and later even formable – fluorescent tubes.

“At that time, acrylic glass clearly was the go-to material for illuminated outdoor advertising,” says Matthias Schäfer, the expert and sector manager for “Visual Communication & Lighting” at PLEXIGLAS®. “It was able to spread the light evenly.” Since then, lighting technology has continued to evolve – and with it signage. At first through ever more efficient and smaller fluorescent tubes and finally through light-emitting diodes, or LEDs for short.

Outdoor advertising makes cities shine

In the 1920s, illuminated advertising was already bathing the streets of large cities in bright light and it has since conquered the entire world. The photo shows a cinema advertisement from 1957.

© Evonik Industries AG, Konzernarchiv Hanau

Outdoor advertising makes cities shine

Through the further development of outdoor advertising, various colors and shapes became possible, as this example from 1977 shows ...

© Evonik Industries AG, Konzernarchiv Hanau

Outdoor advertising makes cities shine

... just like this picture of a well-known circus from 1978.

© Evonik Industries AG, Konzernarchiv Hanau

Special material for illuminated advertising

Over time, acrylic glass became the go-to material for illuminated outdoor advertising. In September 1975, Röhm introduced the “PLEXILUX lighting range”. There were 18 varieties (colorless, white and colored), each made out of cast and extruded PLEXIGLAS®.

© Evonik Industries AG, Konzernarchiv Hanau

PLEXIGLAS® makes a mark

Today, advertising structures made of Röhm’s brand acrylic glass shine around the globe, as here in Leipzig (Germany). The 12-meter-high, illuminated ball with an outer layer made of PLEXIGLAS® LED is the distinguishing feature of the Nova Eventis shopping center. It glows in red, green or blue as selected.

© Röhm GmbH – Acrylic Products

Easy to process

The illuminated letters of the Cotton On store on Queen Street in Auckland City, New Zealand, were made from PLEXIGLAS® LED Block. The material has been specially developed for the signage market. The advantage is that the individual letters can be milled out relatively easily and do not have to be assembled from different parts.

© Röhm GmbH – Acrylic Products

More efficient illuminants

“Illuminated advertising has become increasingly energy-efficient over time,” says Schäfer. “In addition, each new type of illuminant also modifies the design of illuminated signs and letters.” For example, fluorescent tubes dominated illuminated advertising just a few years ago. They were mounted in light boxes behind the surface to be illuminated – or they were shaped and inserted into the recess of milled or glued letters made of plastic. “However, you can’t simply adopt this setup 1 : 1 for energy-saving LEDs,” says Schäfer.

Avoiding differences in brightness

LEDs emit a strong spotlight. This can easily lead to undesired differences in brightness, also referred to as hot spots. LED-operated advertising systems therefore require a very good light-scattering material in order to ensure that the advertising messages are also visually impressive. “The use of LEDs has led to higher requirements for illuminated advertising materials,” says Schäfer. “Only the right combination of illuminant and surrounding material leads to efficient illuminated advertising systems with minimal energy costs.”

Advertising: In the best light thanks to PLEXIGLAS®

Materials for illuminated advertising systems

With PLEXIGLAS® LED, Röhm developed versions of its brand acrylic glass for the special requirements of LEDs in the early 2000s. In one variant, it is particularly suitable for light boxes backlit by LEDs, in which the LEDs are mounted flatly behind the light-scattering material. In addition, the colored variants of PLEXIGLAS® LED are matched to the same wavelength ranges in which red, yellow, green or blue LEDs shine. “This ensures that these colored LEDs are optimally used and the system shines brighter with the same energy input,” says Schäfer.

Moreover, PLEXIGLAS® LED has better light-scattering properties for backlighting than conventional acrylic glass. “Even with the compact designs of light boxes that are possible thanks to LEDs, unwanted hot spots can be largely avoided,” says Schäfer.

Block material for letters

PLEXIGLAS® LED Block has been specially developed for the requirements of the signage market. “This product is known on the market as fully acrylic letters, which have proven particularly suitable for illuminated letters up to a size of 500 mm,” Schäfer explains. The advantage is that the white-colored, highly scattering block material can be machined particularly easily with CNC mills. The LEDs can then be inserted relatively easily into a milled groove. “This is obviously much more efficient to manufacture than having to assemble individual letters from a back wall, a border and a cover,” says Schäfer.

Moreover, moisture can penetrate into the letters less easily and the milled letters are also better able to withstand the temperature changes between summer and winter. And, as Röhm’s brand acrylic glass is inherently resistant to UV rays, logos and large-scale advertising signs retain their color and high quality for a long time. After all, the advertising systems should still look good after many years.

Identical design around the world

© Röhm GmbH – Acrylic Products

PLEXIGLAS® can be easily dyed, enabling an exact representation of a company’s color scheme. This ensures that all the advertising boards of all the branches worldwide look the same. The selected color remains unchanged, regardless of whether it is illuminated or not.

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