kengLEDs’ near-field distribution testing
Abstract:
With the development and application of LEDs,it is becoming increasingly important to be able to measure the performance of LEDs and LED-based systems in accurate and meaningful ways.The intended purpose of the measurement to inform development, to characterize or evaluate finished products, for production quality control, or for in-use performance assessment determines by the photometric and colorimetric quantities which are important to measurement.Considering the evolution of LED from point light source to surface light source,far-field distribution measurement can’t satisfy the measurement requirement.So that the selection of the new measurement about near-field testing method and system is necessary.Near-field testing contains more spatial photometric and colorimetric information than far-field testing,also the far-field characteristic distribution can be extrapolated from the near-field one.In addition,the precise measurement will support LED luminaire design.
Near-field testing has many advantages,such as measuring LED dies and package,supporting optical engineering package design,optical engineering package design,producing headlamps, and so on. Near-field testing measures luminance (spatial distribution) of the LED at many view angles, which includes luminous intensity data. with an imaging detector (CCD camera) rotated about the LED, this test will provides luminance matching view angle data.
A testing system named goniophotometers are designed to very accurately measure the near-field luminance distribution of a light source. It can capture the output light distribution at the source from multiple viewing angles ,gain the corresponding data,then make a near-field model to analyze by a software. Off course this system has a number of physical configurations . With two independent axes of rotation, this system maintains precise positioning between the DUT (device under test) and the imaging colorimeter. With the help of this system, near-field testing becomes easy and accurate.
Key words:
涉日
声波识别 鹿心杜 百科
near-field distribution, measurement, an extended light source, goniophotometers. 1. Introduction:
Measurement considerations consist of clearly understanding the meaningful accuracy required for application, assessing the trade-off between measurement speed and volume of data collected, accounting for the measurement environment, and accounting for device attributes (e.g. LED warm-up). The flowing picture depicts the common ways applicated in LED relative testing. Different programs need different testing methods. For example, luminaires composed of LED arrays with narrow beams can’t use far-filed testing ,because it dosen’t meet the far-field standards a distance of five times the maximal dimension of a light source. In the following context,I’ll show the near-filed testing system.
地效翼船
Figure 1Measurement Domain Chart
2. Near-field testing
Usually,a point measurement from one viewing angle or a single integrated measurement will suffice.In fact,when it comes to the package,even a little variation of LED’s place will lead to variation of luminance and color with angle.As for LED luminaire,it can’t be treated as point light,instead,consideration of the spatial distribution affected by light output from point to point on the source.Therefore,accurate measurement requires more detailed distribution.
Near-field Imaging goniophotometers (figure 2 below) are especially designed to measure non-point source,such as large light sources, Surface light source. In general though, the potential complexity of a light source as a system and the potential for error in theoretical understanding are sufficient to make a measurement preferred, as it is a real description of the source. Of course for evaluation, inspection, or control, having the real data specific to a device is necessary as the measurement is the point. So goniophotometers should have a sufficiently small field of view to allow enough CCD pixels to map to the surface of the light source to see any relevant fine scale detail on the LED die or device.
Figure 2Goniophotometers
By using a CCD-based imaging photometer as a detector on a goniophotometer, modern near-field goniophotometers allow the determination of the starting point and the direction of the emitted radiation of a light source expressed by a set of rays (near-field model). The various near-field goniophotometers available on the market are nowadays used for generating ray data (“ray files”), which are commonly employed for optical simulation tools for the computer aided design of modern luminaries, like modern headlamps which LEDs as light sources.
Near-filed testing will collect light data at a distance less then five times of light source’ diameter which is used in far-filed testing. In this case, light distributions are complicated and ample. Also complete description of light radiation on the basis of the ray data and luminous flux measurement with integrated photometer through integration of the illuminances will add to validation.sgjt
豫公网安备41160202000603
站长QQ:729038198
关于我们
投诉建议