Luminous flux what is

The rate of decline is mostly influenced by temperature, with the fastest rate of decline happening at the highest temperatures. This is why LM requires testing to be carried out at 3 different temperatures. This also why manufacturers go to considerable lengths in luminaire design to ensure that the LEDs they use are kept within their specified temperature range. An LM report will usually show data collected over 6, to 10, hours.

However, when many lighting applications require the life of an LED to be many times this it is necessary to project the data into the future to determine how it might perform after several years of use. There are many ways that data can be projected, some of which would be downright misleading.

This defines precisely what arithmetic formulae are to be used to project data gathered over, say 9, hours, out to 30, or more hours. Manufacturers will often talk of L80 or L70 for example as if they were points in time. Techopedia Terms. Connect with us. Sign up. Term of the Day. Best of Techopedia weekly. News and Special Offers occasional. Luminous Flux. Techopedia Explains Luminous Flux. Luminous flux is the measure of perceived power of light by the human eye. We measure luminous flux in lumens, just as we might measure speed in miles per hour.

Why don't we just say "brightness"? Well, luminous flux is measurable, unlike brightness which is a perception. Brightness means something different to everyone, just like 'fast' to one person is 'slow' to another. That said, you'll always see me writing "appear brighter" and "perceived brightness", since brightness is different for everyone.

The more lumens a light source outputs, the brighter the objects being lit by said source will appear. Notice I again said "appear". That's because lumens do not take into account the area over which the light is spread.

In photometry, illuminance is the total luminous flux of light incident per unit area. In other words, luminous flux represents the total amount of light emitted by the source, while illuminance refers to the total amount of light received by an object. The relationship between illuminance and luminous flux is similar to that between Irradiance and radiation flux , that is, the radiation flux received per unit area.

However, the illuminance is weighted according to the sensitivity of human eyes to light of different wavelengths, which represents the light intensity perceived by human eyes. The SI unit of illuminance is the lux lx. It is equal to one lumen per square meter. In photography, there is also a non-metric unit of illumination, foot-candle. Foot-candle means "the illumination of a candle source on a surface one foot away. Illuminance is the number of lumens per square meter.