Spectral Power Distribution (SPD) refers to the representation of the power of light emitted by a source across different wavelengths. It shows how much energy is present at each wavelength, typically measured in nanometers (nm). This information is crucial for understanding how light interacts with materials and affects human perception, such as color and brightness. SPDs are often used in fields like photometry, color science, and lighting design. By analyzing an SPD, researchers and designers can determine how a light source will appear in various environments and how it will influence the appearance of objects illuminated by that light.