It is illustrated that principles of light can be used by investigators to find and enhance evidence. Certain ALS systems can be valuable tools in that they offer high performance, affordability, and versatility. There are many different ways to use ALS systems. The three methods shown here (absorption, diffused reflection, and photoluminescence) are the most common and can be used to find evidence. These light sources have proven valuable tools in forensic work. Other techniques are also available and may be explored in the future. This article reviews the theories typically used to describe light’s properties (wave theory and particle theory) and light’s usefulness in the field of forensic sciences, and it examines three different ways in which ALS systems can be used to find evidence.