Application Setup: LED Analysis

A USB4000 Spectrometer optimised for LED measurements is configured with a Grating #2, a 350-1000nm wavelength range, a 25µm Slit entrance aperture and an L4 Detector Collection Lens to increase light efficiency and reduce stray light. With this configuration, optical resolution is ~1.33 nm (FWHM). An OFLV-350-1000 Order-sorting Filter eliminates second- and third-order effects. This optical bench configuration maximises system sensitivity, mitigating the light loss inherent with use of an integrating sphere - the sampling optic of choice for most LED applications. (You also can collect LED signal with a CC-3-UV Cosine Corrector and fiber.)

The LED is mounted in the NIST-traceable LED-PS-NIST LED Power Supply, which provides a white background for the LED and a controlled drive current to characterise LED output. The FOIS-1 Integrating Sphere is placed over the LED-PS-NIST and collects the LED output. In this configuration, the integrating sphere measures the forward (or partial) flux in Watts/nm or lumens from the LED.The attached optical fiber collects the forward flux from the LED and transmits it to the USB4000 Spectrometer. The power and colour of the LED is determined by comparing the LED to a standard - the LS-1-CAL-INT Calibrated Source, which fits into the sample port of the FOIS-1.

The FOIS-1 integrating sphere has a diameter of 38mm and an entrance port size of 9.5mm. For measurements of the total flux from LEDs and LED clusters, as well as LEDs fitted with reflector housings or lenses, we offer a family of larger integrating spheres from Labsphere with diameters from 15cm to 2m.

The LED-PS Power Supply provides three useful functions: securing the LED in place; powering the LED; and displaying the LED’s drive current. Use the adjustable drive current feature to increase or decrease an LED’s current up to 50 mA. We offer a standard LED-PS and a NIST-traceable version.

The LED is powered by the LED-PS and is inserted into the 9.5mm diameter port of the FOIS-1 Fiber Optic Integrating Sphere, which has a 360° field of view. The P400-2-VIS-NIR Optical Fiber collects the light from the FOIS-1 and funnels it to the USB4000 Spectrometer.

The LS-1-CAL-INT is a NIST-traceable light source designed specifically to calibrate the spectral response of a spectroradiometric system that uses the FOIS-1 as the sampling device. It provides known absolute flux values at several wavelengths. The LS-1 is used as a reference for relative power measurements.