Photometry is a branch of optics and lighting science that deals with the measurement of light intensity and other characteristics. Photometry studies are often used in the design of indoor, outdoor, and architectural lighting systems in order to determine their overall efficiency, yield more accurate results than analysis of diagrams and calculations. The measurements taken during photometry include luminous flux, illuminance (a measure of the amount of light falling on a surface), luminance (the reflectance of that light off a surface), color temperature (temperature measured in Kelvin units) and chromaticity coordinates. Each measurement factor is then weighted differently to arrive at the overall result. In most cases, these measurements are taken using special instruments called photometers which can measure even tiny differences in light intensity over large distances and across different surfaces. These instruments are also very sensitive to glare – meaning that they can be used to detect excessive brightness or contrast between two areas which make it difficult to see clearly or navigate paths safely. In lighting design projects, this information can then be used to adjust levels in order to improve visibility or reduce glare for better energy efficiency without sacrificing clarity or comfort for users.