The total light quantity of a lighting device which is emitted in every direction is called luminous flux. The unit of luminous flux is lumen.
Perhaps the most significant measure among the lighting devices is lumen value.
The total amount of light, which is visible to human eye, emitted from a light source is expressed in lumens. So, a lamp or a light fixture with high lumen value means the higher light output.
If we use a general and simple expression, it can be said that lumen is equal to brightness.
The symbol of lumen is lm and it is used after the numerical expression. For example, 300 lm, 500 lm, 1.000 lm, 10.000 lm.
In lighting sector, different technologies emerged day by day. Lumen values are increased with all technological steps, although the electrical consumption of lighting devices reduces. For example, in past, we used to spend 75W power to get 1000 Lumen. Today, we can obtain this brightness with 10W power.
The necessary amount of lumen in a lighting application depends on some variables such as; size of the room, ceiling height, painting, lamp type, and placement.
Although the manufacturers and importers stated the lumen value on their products, it is not always reliable information. Because, in order to specify the lumen value of a lighting device, measurement should be done in laboratory conditions. A very small amount of manufacturer does a measurement in this way. Especially, most of the manufacturers operating in the field of LED lighting industry writing the total lumen value on the products. However, it should be reminded that, if the LEDs are included in a system, light loses can occur.
Beside these loses, decrease in light outputs can be seen during the light sources are used. That is why some consumers are observed that brightness of the lighting device reduced overtime.
Lumen is related to lux unit which represents the light level. High lumen means, high level of light or lux. If you complain about the light level or insufficient lighting in a place, lamps can be replaced with high lumen value ones or increase the number of lams in order to obtain brighter lighting.