Home LED BasicsKnow More about Luminous flux and Lumen When Buying Bulbs
Know More about Luminous flux and Lumen When Buying Bulbs

Know More about Luminous flux and Lumen When Buying Bulbs

What is luminous flux and lumen?
1. Luminous flux (Ф) refers to the amount of visible light that light source emitted per second. (The wavelength of visible light is between 380 ~ 780 nm and the other amount of radiation wavelengths cannot be as luminous flux.) Because we human eyes got different relative vision rates to the different light wavelengths, so even if the different light wavelengths got the same radiation power, we cannot say the luminous flux is the same, that is to say in that luminous flux is adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light.

2. The lumen (symbol: lm) is the SI unit of luminous flux, a measure of the total “amount” of visible light emitted by a source. The higher the lumen is, the brighter the light is. One lumen is defined as the luminous flux of light produced by a light source that emits one candela of luminous intensity over a solid angle of one steradian. In other systems of units, luminous flux may have units of power. The lumen is defined in relation to the candela as

1 lm = 1 cd·sr

A full sphere has a solid angle of 4·π steradians, so a light source that uniformly radiates one candela in all directions has a total luminous flux of 1 cd·4π sr = 4π cd·sr ≈ 12.57 lumens.

3. To measure the light flux of bulb, commonly used measuring instrument is integral ball also called the light flux meter. All visible light that emitted from light source can be gathered in the sensor and make it easy to measure.

lumen and luminous flux


How many lumens will be enough in a room?

Many people will have a question like: how many lumens are needed in a room? How much light is enough in my daily life? Is there a standard answer? Actually there is not, because different people have different sensitivity and adaptability for light and the answer is also related with the different position of the light source and the different decoration of the room. However, we can estimate the brightness of same designed light bulb according to the luminous flux, if you feel the light bulb is too bright to use, the next time you can use the bulb with lower lumen to replace it.

On September 1, 2010, European Union legislation came into force mandating that lighting equipment must be labelled primarily in terms of lumens, instead of watts of electric power consumed. That will help people to make comparison and choice, so if you have any requirement on the brightness of the light bulb, just check the box in detail data.

find the lumen


How to Convert LED Watts to Lumens?

The lumens of Luminous flux is a reliable way to measure the bulb’s brightness, we can replace the old lamps or choose the new lamps according to the lumens value, in that way we can ensure we bought the right and perfect lamps and neither too bright nor too dark. If you want to buy some decorative light or mood lighting, it will be better to choose some low flux (below 600 lm) lights. Because incandescent lamp are phasing out, when we choose and buy the light bulb you can refer to the ErP rules that when CFL, halogen lamp and LED bulbs replaced incandescent lamp with different power, how many luminous flux are needed.
calculating the lumens

From the picture above, we can see that the brightness of LED light with 806lumens is equal to the brightness of 60W incandescent light. If you want to replace 100W incandescent bulb with LEDs, you will need a LED light with 1521lumens.


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