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Variable Message Signs

Variable Message Signs

Variable Message Signs (VMS), also known as Dynamic Message Signs (DMS), often consist of a bank of yellow and red LEDs behind a protective sheet of Polycarbonate.  The Polycarbonate is used to protect the sign against impact and environmental damage.

Recently technical standards such as European Standard EN.12966 have been introduced; these standards have introduced test methods that simulate the reflection of the sun off the sign when the sun is at a low angle in the sky.  The concern is that the reflection of the sun off the Polycarbonate face can make the LED sign unreadable by drivers.

HighLine Polycarbonate has introduced a range of Polycarbonate sheet that has been optimized for use in VMS and DMS applications.  The sheet aims to reduce the reflection of the sunlight and increase the transmission of LED light through the sheet.  The sheet formulation has been optimized to increase this benefit at the wavelengths used by Red LEDS (590-595 nm) and Yellow LEDS (635 nm).  By reducing reflection of the sunlight and increasing the transmission of the light from the LEDs, the signs are much easier to read in all conditions.

The Variable Message Sign Grade of Polycarbonate sheet is also offered with a anti-reflective hard coat which not only improves the reflection and light transmission properties, but also gives the sheet enhanced abrasion resistance and protection against UV weathering.  HighLine Polycarbonate recommends this anti-reflective hard-coat for all outdoor VMS applications.

 

Light Transmission Data  (3mm / 0.118” thick sheet)

General Purpose  Polycarbonate (*)

VMS Polycarbonate

VMS Polycarbonate with Anti Reflective Hard-coat

Red LEDS (590-595nm)

86.0%

89.7%

92.0%

Yellow LEDs (635nm)

83.8%

89.0%

91.0%

(*) The General Purpose Polycarbonate was purchased from a distributor and was manufactured by a major US producer as their standard product.

Reflection and Glare reduction

VMS Polycarbonate with an Anti-Reflective Hard-coat reduces reflection by 25% compared to General Purpose Polycarbonate.  It is also possible to add an anti-glare additive to the hard coat to further reduce the reflection of sunlight back to the drivers of vehicles.  Both the anti-reflective hard-coat and the anti-glare additives significantly improve the readability of the sign under the most extreme conditions.

For additional information about our VMS grade polycarbonate sheet contact our technical team.

 

 

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Datasheet – Variable Message Signs (VMS)