Lambert’s Cosine Law

Lambert’s cosine law explains that the intensity of radiation emitted by a surface is directly proportional to the cosine of the angle between the direction of the emitted radiation and the surface normal. In the context of infrared measurements, this law means that the emitted infrared radiation is strongest when observed perpendicular to the surface and weakens as the angle increases. This principle is crucial for accurately interpreting infrared thermometer readings, as it affects the apparent emissivity and intensity of the measured radiation. When using an infrared thermometer to measure temperature, it is important to consider the angle of measurement to ensure that the readings accurately represent the surface’s true temperature.

Significant deviations from perpendicular angles can result in lower detected radiation intensity, which could lead to underestimation of the actual temperature if not properly adjusted for in the measurement setup.