What is luminous flux?
Luminous Flux is the physical quantity that measures the total amount of light emitted by a light source (LED or a LED lights fixture), is a key part of LM-80 test, usually represented in lumens (lm).Luminous flux is usually measured using an Integrating Sphere. It reflects the light-emitting capability of the light source within the visible spectrum and is unrelated to ultraviolet or infrared radiation, as these do not contribute to luminous flux.
Luminous flux – Professional analysis
In physics, the lumen is the amount of light produced by 1 watt of radiant power at a specific wavelength. For example, at a wavelength of 555 nanometers, 1 watt of radiant power is equivalent to 683 lumens. This definition takes into account the human eye’s sensitivity to different wavelengths of light, meaning that different wavelengths of light, even with the same power, will feel different in brightness.
Luminous flux – Understanding by others
In the lighting industry, “lumen output” or “lumen packaging” are common terms used to describe the brightness of a light source, synonymous with luminous flux, and also measured in lumens. You can imagine it like asking how much heat a central heating boiler produces; the brightness of a light source can also be quantified in lumens.
Luminous flux in the LM-80 test
The LM-80 test is an important experiment for evaluating the performance of light sources, where the measurement of luminous flux is a key part. At the beginning of the test, luminous flux is set as a 100% baseline (L100), and then re-measured regularly during the test process to observe changes in luminous flux over time. Typically, luminous flux will initially increase and then gradually decrease, a phenomenon known as lumen depreciation.
Temperature influences luminous flux
The rate of lumen depreciation of LEDs is significantly affected by temperature, with faster depreciation in high-temperature environments. Therefore, the LM-80 test requires tests to be conducted at different temperatures to ensure the accuracy of the results. Manufacturers pay special attention to the temperature control of LEDs when designing LED lights fixtures to maintain their performance.
Long-term prediction of LEDs
The LM-80 report usually provides data for 6000 to 10000 hours, but many lighting applications require a longer service life. To predict the performance of LEDs in the coming years, the Illuminating Engineering Society of North America (IES) has established the TM-21 standard, which provides an accurate prediction method to ensure the comparability of data from different LEDs and manufacturers.
Misunderstanding about LED lifespan
The terms L80 or L70 often mentioned by manufacturers actually refer to the point in the LED’s lifespan when the light output drops to 80% or 70% of the initial value. The rated life of LED lighting fixtures usually refers to the estimated operating hours when reaching L70. It is important to note that after reaching the rated life, the luminous flux of LED lighting fixtures will continue to decrease gradually, which is different from the performance of old light sources such as fluorescent lamps and HID lamps. CPS LIGHTING various lighting fixtures are all aged tested and reliability tested before leaving the factory. If there are dead LEDs or serious light decay, the reasons will be analyzed in detail to improve the defects of the lighting fixtures and improve the reliability of the lighting fixtures.
