LED Measurement Applications

The measurement of LED's presents unique application requirements for which we offer the appropriate instrumentation and applications experience to assist customers in configuring a system.

Many years of working with LED applications has prompted the development of a variety of system configurations that meets most LED metrology requirements. Light Emitting Diodes can be measured in a wide variety of colours and brightness, so accurate measurement of the LED is therefore essential. This can be done in two ways - photometry and radiometry.

Photometry relates to visible radiation alone, just as the response of the human eye. Radiometry goes beyond these limitations. In both photometry and radiometry, the LED can be characterised in emitted power or in intensity. Emitted power is all the power (flux) emitted from the LED in lumens or Watts, collected and measured without regards to the direction of the flux. The intensity is the ratio of the flux, leaving the source and propagating in the element of solid angle containing the given direction, and is expressed in candelas.

For basic measurements of photopic parameters and irradiance (excluding flux), a system is typically configured with a AvaSpec-ULS2048-USB2-FCPC spectrometer, a 25 or 50µm slit and 300 line/mm grating covering the range from 360-1100nm, providing 1.4-2.4nm full width half maximum (FWHM) resolution. A 2m fibre optic cable (FC-UV200-2-FC-SMA) is mated to the instrument and terminated in a cosine function diffuser (CC-UV/VIS/NIR) which has 3.9 mm diameter surface area. The entire system is irradiance calibrated with a NIST source over the specified wavelength range for spectral irradiance (µW/cm2/nm). This calibrated system can be operated using Avantes proprietary AvaSoft-IRRAD software which provides the following parameters - X, Y, Z, x, y, z, u, v, CRI, Colour Temperature, Dominant Wavelength, Complementary Dominant Wavelength, FWHM, Centroid, Peak Wavelength & Purity. In addition, raw data in scope mode is displayed, as well as the X-Y chromaticity diagram. As an option, the system can be configured with longer fibre lengths and the AvaTripod to hold the diffuser in place during measurement. The system can be controlled via Avantes dynamic linking library (DLL) interface through LabView, C#, C++ and a number of other programming environments.

For flux measurements, the entire LED must be inserted into the port of an integrating sphere. Avantes offers a complete line of integrating spheres ranging from 30-200mm (internal diameter) to facilitate this.

For system calibrations by the enduser, we offer the AvaLight-HAL-CAL calibration sources which are offered in configurations that are compatible with cosine diffusers and small format integrating spheres (30, 50, 80mm).