The present invention relates to compositions and an apparatuses for determining protease activity. This is significant because it allows an operating system to schedule other threads for execution within deterministicpredetermined time parameters. A fraction of incident optical energy directed to the intermediate focus is different from a fraction of incident optical energy directed to at least one of the near or far foci. During use, light from the light source interacts with the tube of color shifting film, producing a brilliant colored effect.