Graphic analysis LED street light effect definition and measurement method

In many domestic LED street lamp manufacturers, in order to declare the high light efficiency of their products, the initial light flux of the chip is divided by the power consumption of the light source to obtain the ratio, which is the data of high luminous efficiency of the product. In fact, this is a confusion concept. In order to let everyone understand, I will explain these two concepts below:

1. Initial luminous flux is the amount of light energy that arrives, leaves, or passes through a curved surface per unit of time, in lumens (lm). Luminous flux is usually expressed in terms of Φ.

2. Actual luminous flux refers to the amount of light energy that is emitted from a light source when it is turned on, through a lighting device (such as a lens or a lamp cover, etc.) until it reaches the working plane where it is needed. We call the luminous flux reaching the working plane the actual luminous flux.

Through the introduction of the above two points, it can be known that the actual luminous flux value is smaller than the initial luminous flux. See below.

By the definition of Guangtong, we immediately lead to another important concept: light efficiency.

Efficacy is the ratio of the total luminous flux emitted by a light source to the electrical power consumed by the source, in lumens per watt (lm/w).

Because there are two kinds of data, initial light flux and actual light flux, the light effect has two different data of initial light effect and actual light effect.

We know that the reason why the "Ten Cities and Ten Thousand Miles Project" promotes LED street lights is completely energy-saving and carbon-reducing. The initial luminous flux of the chip passes through the lens cover and reaches the road surface to illuminate the pedestrian vehicle, which is the actual luminous flux. What we need is the high luminous efficiency brought about by the actual luminous flux, not the high luminous efficiency required by the initial luminous flux.

Nowadays, the Led Street Lamp industry blindly promotes the high luminous efficiency of the initial luminous flux, and many manufacturers have also played a role in fueling this. Some merchants have launched 120 lm/w high-efficiency LED street lights, the world's first light-effect LED street lights and other promotional slogans. The reason for this situation is precisely because the unified standards of the country or industry have not been formulated, and the relevant testing standards have not been implemented. In addition, although some places have introduced local standards, such as Guangdong's DB44 standard, Shenzhen LED specifications, etc., but the standards are not uniform. Take DB44, for the LED Street Light applied to the high-speed main road, under the premise of 4000K~6500K color temperature, the Class I standard is not less than 78 lm/w; the Shenzhen specification defines the initial light efficiency to be no less than 60 lm/w. However, the Shenzhen Code additionally mentions that the energy efficiency rating criteria are: Level I energy efficiency must be at least 80 lm/w. DB44 and Shenzhen specifications have been released according to the actual situation of the place. It can be seen that the differences between different places are still relatively large. Therefore, the state should formulate uniform industry standards and unify the norms as soon as possible, so that each region will have rules to follow.

Although the domestic standardization of standards is still under discussion, on December 3, 2009, after three drafts were issued, the US Department of Energy DOE issued the final version of the ENERGY STAR LED lighting standard, which was requested on August 31, 2010. Effective.

To this end, we read a lot of information for research. The second draft of the three SSL luminaire performance standards released by the US Department of Energy DOE on July 1, 2009, pointed out that other indicators still can not fully measure the energy efficiency of the luminaire. Therefore, the draft proposes a new metric---Fitted Target Efficacy. It is also required that the minimum light output of outdoor road lighting should reach 1000 lm (initial luminous flux).

FTE takes the “target illumination area” as the research object. Therefore, FTE has two key assumptions:

1. Rectangular distribution can cover the largest area and is more effective than circular distribution. See below.

2. The white circle is the light source, the green part is the area where the target illumination area is effectively illuminated, the red part is the area where the target illumination area is not effectively illuminated, the black area is outside the target illumination area, and falls in the black area. Luminous flux should be discarded. See below.

The formula for calculating FTE is as follows:

FTE=(green area luminous flux* green area area as a percentage of the total area of ​​the green and red areas) / luminaire input power

It can be seen from this that the US Department of Energy issued FTE as the future LED energy efficiency formulation, which is very reasonable.

We are very opposed to blindly promoting the high luminous efficacy of the initial light. In the road lighting, only a reasonable illumination is needed. The so-called "the brighter the better, the higher the light efficiency is, the better", which is not suitable for the current energy-saving and carbon-reducing forms, and does not meet the true pursuit of human visual health. We should rationally treat the prospects of LED street lights and not blindly follow them. Only by having a correct, objective and mature mentality, having a rational and solid analysis, and having basic and practical research can make the LED industry develop rapidly and steadily.

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