The Measuring Method for the White LED Lighting

This standard is limited to the white LED lighting, which has declared that the LED test target will be limited to white LED lighting in order to limit the measuring method of comparing with the standard LED in order to effectively improve the measurement precision, and make a very detailed regulations for the contents of the standard LED. In the part of light intensity measurement, the measurement should be in accordance with the measurement standard conditions required by the International Committee on Illumination. In the part of the flux measurement ( Flux Meter ), integrating sphere should be used for the measurement, and the chromaticity, relevant color temperature (Correlated Color Temperature; CCT) ( Color Temperature Meter ), color rendering index (Color Rendering Index; CRI) and other measuring method should be added in the revised edition, and in principle, the integrating sphere is used as its incident optical system.

The definition of the white LED lighting explicitly presents the greatest difference between this standard and other LED’s standards, namely it has made a clear definition for the white LED lighting. According to this standard’s explanation, the measurement of the flux or the light color ( Colorimeter ) of the average light intensity of the so-called “white LED lighting” must meet three conditions: the spectrum (Spectrum) should almost cover the whole range of the visible light field without the lack parts; The scope of the relevant color temperature should be within 2500 ~ 10000 K; And the relevant color temperature should be in the CIE 1960 Uniform Chromaticity Scale (UCS); The deviation with Planckian Locus must be less than 0.02.

Note that in this definition, the RGB LED will be ruled out of the scope of the white LED lighting. In fact, in this standard accessories explanation, the definition of white LED lighting is a controversial project. In the provisions of the relevant color temperature, because here aims at the general lighting, it starts with the consideration of the same degree (the relevant color temperature is 2700 ~ 8000 or so) with the fluorescent lamp. But at present, with the reference of the actual development technology of the white LED, the scope of the relevant color temperature is set in the range from 2500 K to 10000 K.

The light intensity measurement and the flux measurement are the two major measuring methods. Because there is no standard and unified LED packaging shape, size and light distribution characteristics, the different design structure is produced based on all kinds of purpose. Therefore, LED measurement is rather difficult. So, the structure, properties and reproducibility of the standard LED need to be stipulated.

In this international standard, the standard LED is mainly divided into the light intensity measurement and flux measurement (see table 1); it has the different design concept based on the different measurement characteristics. For example, the standard LED used for the light intensity measurement adopts the bullet type (lamp) package for the easy alignment with the mechanical axle as the standard form, because in the light intensity measurement method, the measured LED mechanical axle photo detector is an very important correction factors; As for the standard LED used for the luminous flux measurement, considering the measurement provision of the total luminous flux, it can be used to prevent giving off light toward the rear of the LED, and the metal cans type (TO-Can) package with more uniform light intensity is taken as a standard form. It is worth noting that, here both the two forms of standard LED use the white LED made of the indium gallium nitride (InGaN) series of chips together with the yttrium aluminum garnet (YAG) phosphor, its corresponding definition for the white LED lighting is the part of no lack of the wavelength stated in the definition.

Because the standard LED ( LED Tester ) is an important reference for the measurement, therefore, this standard tries to lower the stability of the optical and electrical characteristics by reducing the influence of the surrounding environment, in order to achieve the expected reproducibility requirements. In addition to limit the environmental temperature of the measurement to be less than 2 ℃, this standard suggests that it is better to use the standard LED driven by the constant current which has already experienced over 100 hours (such as 20 ma) to reduce the LED early changes, the environment temperature of the standard LED must be controlled in25 ℃. The instruction of the temperature control slot (Socket) (a chip temperature control function of the light fixture) is added in annex 4 of the revised edition. It requires that under the condition of constant current, the time for the LED to get to the state of the thermal ( LED Thermal Performance) equilibrium is expected at least in 5 minutes or more before the light measurement.