What is the difference between PAR and LUX?

PAR (Photosynthetically Active Radiation) and LUX (Luminous Flux in Units of LUX) are both units of measurement for light, but they refer to different aspects of light that are important in different contexts.

1. PAR (Photosynthetically Active Radiation):

PAR specifically refers to the portion of sunlight or artificial light that is used by plants for photosynthesis. It is the light in the visible spectrum (typically between 400 to 700 nanometers) that plants can convert into chemical energy. PAR is crucial for plant growth and development, as it is the primary source of energy for the photosynthetic process. Light meters that measure PAR typically give a reading that indicates the intensity of this specific light range. Is expressed as micromoles per square meter per second (μmol/m²/s).

2. LUX (Luminous Flux in Units of LUX):

LUX is a unit of illuminance, which is a measure of the amount of light that reaches a surface. One lux is equal to one lumen per square meter. LUX is used to describe the overall brightness of a light source as perceived by the human eye. It takes into account the entire visible spectrum (approximately 380 to 780 nm) and is weighted with a standard photopic vision spectrum, which simulates the sensitivity of the human eye to different wavelengths of light. LUX is important in lighting design, photography, and other fields where the quality and quantity of light affecting human vision are concerns.

LUX, on the other hand, measures the illuminance or the total amount of visible light that falls on a surface. It is not specific to the wavelengths of light that are utilized for photosynthesis by plants. LUX is commonly used to measure the brightness of light in settings such as indoor spaces, outdoor environments, and in horticulture to some extent.

In summary, while both PAR and LUX are measures of light, PAR focuses on the specific light range (400-700 nm) that is used for photosynthesis by plants, whereas LUX measures the overall brightness of light as it affects human vision across the entire visible spectrum.