Silicone encapsulants are used for a variety of photonic and optoelectronic applications where they function as a photon guide to increase the device's functionality such as light output for an LED. The purposes range from light guides to increase signal strength, waveguides to increase viewing angles and to increasing the light output of an LED. Silicones are highly desired since they are transparent in the visible range as well as maintain their optical clarity and mechanical properties under harsh thermal conditions. Other polymeric materials, such as epoxies and urethanes, can degrade which negatively impacts the device's performance. The need to understand the thermo-optic stability of the encapsulant over time is very dependent on the conditions of the device itself. Variables that affect the material properties include but are not limited to; wavelength, temperature, exposure to air, and encapsulant thickness. Since it can be said that there are almost an infinite amount of possible combinations the material can be exposed to, the silicone supplier must use develop a method to uniformly expose the materials to heat and then measure response in order to give end users the most relative comparisons of how different materials perform. The work presented is the method developed for exposing materials to 150 ° C in air for 8,000 hrs and determine the change in transmission in the visible region of the UV-Vis spectrum. It was found that there are key variables that can affect the results and this will be discussed to help the end user interpret the data.