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Photometric Laboratory

Date posted: 16/03/2013

By investing in a modern full scale goniophotometric laboratory, MESTAR strengthens its test and measurement capacities and underlines its commitment to strengthen its in-house capacities for providing Vietnam markets with products of highest quality and modern design.

                                                                                                                                            Photo: Photometric Laboratory 

Functional Principles

The luminous intensity distribution of a luminaire is determined by measuring its illuminance at a given distance in all possible directions in space. The LMT GO-DS goniphotometer has therefore two independent rotational axes. The goniophotometer consists of a rotating luminaire holder, a rotating mirror, and a fixed photometer. The measurement procedure is executed by rotating the luminaire around the mirror at a fixed radius, whereby the mirror deflects the light emitted by the test object towards a photometer. 
By employment of a mirror the test objects can be positioned in such a way so that they remain in their designated burning position with respect to gravity throughout the test procedure. This is essential when testing light sources whose photometric performance is orientationally sensitive.

Test Data Recording

During each measurement, the computer records illuminance or luminous intensity, the corresponding angles of radiation, as well as electrical operational parameters of the measurands and saves this data for further evaluation. The individual test routines can be programmed by LIGMAN Engineers in the software interface. Luminous flux , scaled luminous intensity distribution (cd/klm), light output ratio, averaged luminance, glare as well as the chromaticity coordinates, correlated color temperature and color rendering index, spatially averaged, are calculated automatically. The measurement data are presented in tabular form and as polar diagrams in C -plane pairs portrayed opposite of each other. For importing data into commercial calculation programs such as RELUX, DIAlux, TunLight, etc., the measurement data are recorded in numerous formats including CIE, CEN, EULUMDAT, IES, etc.

                                                                                                                      Photo: Integrated Sphere with computer

Luminous Flux Measurements
While the absolute luminous flux of light sources can be tested on the GO-DS, for rapid testing of luminous flux of lamps and SSL modules in large numbers the substitution method in an integrating sphere is the method of choice. In this case,  the measurands are tested against standard light sources with similar geometric and photometric properties which have been calibrated according to the absolute method.

For this purpose MESTAR has selected the LMT UL 2250/1650 model Integrating Sphere system.The integrating sphere is specially configured in compact design allowing for testing of light sources up to 1.6m length. The outstanding characteristic of this instrument is the very low spectral throughput of the entire system of f1′≤0,1%.

The German manufacturer achieves this by employment of a proprietary photometric coating (BaS,) with variation in uniformity of response in VIS range of < 1%. in combination with an LMT Photometer employing LMT Mosaic Filtering®. This limits spectral mismatch indices to ≤2% when testing most any type of lamp including LEDs. This performance eliminates the need to work with spectral mismatch correction factors to compensate for uncertainties caused by different spectral distributions of standard lamp and measurand. 

LMT will supply the sphere to MESTAR with a special port and test bench for testing light sources in 2 pi orientation mounted to the exterior of the sphere. This test orientation is recommended for testing of forward emitting SSL lighting by the IES LM 79-08. 

The test results including luminous flux, temperature and lamp stability over time, as well as electrical parameters are recorded by the integrated software and made available to MESTAR engineers in recognized file formats for further evaluation.

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