Luminous Flux

Lumen (lm) is the SI unit for luminous flux. One lumen denotes the luminous flux emitted by a light source generating 1 candela (cd) of luminous intensity within a solid angle of 1 steradian (sr).

1 lm = 1 cd x 1 sr

Luminous flux is related to power through the concept of luminous efficacy, which measures how well a light source converts electrical power (in watts) into visible light (in lumens). The maximum theoretical luminous efficacy is approximately 683 lm/W for monochromatic light at a wavelength of 555 nanometers, where the human eye is most sensitive.

Luminous flux is mostly applied in lighting design to improve lighting and visibility. Here are some examples:

1. Home and Office Lighting: It determines the total light output of light bulbs and fixtures in homes to ensure adequate illumination. In workspaces, appropriate luminous flux levels can reduce eye strain and fatigue among employees, thereby enhancing their performance and comfort. Therefore, luminous flux directly influences the choice of light fixtures, effectively determining their brightness and efficacy in illuminating spaces.
2. Automotive Lighting: It helps to ensure that vehicles’ headlights and taillights have adequate lighting and can be seen by other drivers. It also ensures the appropriate illumination level inside the vehicle for comfort.
3. Street and Public Area Lighting: Engineers calibrate street light systems using luminous flux measurements, enhancing visibility and safety on roads. Proper lighting design in parks and public spaces ensures these areas are well-lit and safe at night.
4. Emergency and Safety Lighting: It ensures that emergency signs, like exit and warning signs, are visible in low-light or smoky conditions during emergencies. Emergency Lighting Systems rely on adequate luminous flux to illuminate during power outages.