Due to its numerous advantages, acrylic is one of the most used plastics for outdoor applications, including decorative lighting fixtures. In fact, it’s especially well-suited for outdoor lighting components given its light weight, high resistance to ultraviolet energy (UV), high transmittance and clarity, as well as scratch resistance.
And acrylic has been used in everything from skylights to WWII bomber bubbles and today’s airplanes without yellowing despite years of sunlight exposure.
Acrylic’s chemical structure makes it less suspectable to discoloration and embrittlement.
Resins with ester linkages are susceptible to bond scission (breakage) upon UV exposure. This bond scission can lead to chain scission, which ultimately weakens a material and makes it more prone to cracking and yellowing.
On the other hand, acrylic is a polymer made from methyl methacrylate monomers, which do not contain ester linkages. Acrylic’s polymer backbone contains repeating units of methyl methacrylate monomers. They’re joined by strong covalent bonds that aren’t easily broken down by UV radiation.
Additionally, polymer resins that contain aromatic rings absorb UV radiation and can act as photooxidation initiators, leading to further degradation of the material. Acrylic doesn’t contain these susceptible chemical bonds, adding to its stability when exposed to UV energy.
To further protect acrylic, resins have inhibitor compounds. These compounds block or reflect UV wavelengths to protect acrylic from UV degradation by preventing the bond and chain scissions. As a result, acrylic will retain its color, clarity, mechanical strength, impact resistance, and have an extended lifespan.
There are several other considerations regarding the UV stability of acrylic that should be taken into account when designing products for outdoor applications. These include:
The yellowing index can be used as a predictor of an acrylic’s propensity for yellowing.
The yellowing index is actually a measure of the changes that a material (such as acrylic) exhibits over time due to thermal, light, and environmental factors.
The higher the yellowing index, the more an acrylic will yellow and become discolored. The yellowing index is typically measured on a scale of 0-100, with 0 being no yellowing and 100 being the most severe yellowing.
The optical design advantages of acrylic.
Polymer resins such as acrylic can be injection molded for optical features that are smaller, better formed, and allow for more precise geometric features than pressed glass. As a result, acrylic lighting components are capable of controlling light, having the ability to put light where it’s needed most.
For more information, talk to an Outdoor Lighting professional.
See Cooper Lighting Solutions fixtures featuring acrylic instead of glass.
