High power LED based standard lamps for luminous flux and luminous intensity

BelGIM together with Cersys Analitycs designed and manufactured LED-based reference lamps. The lamp was originally designed for use not only as a part of the national measurement standards, but also as a transfer standard for verifications and calibrations of customers' equipment. Our analysis of the sources of uncertainty of the LEDs' photometric parameters (associated with the light source itself) showed that the main ones are the uncertainties caused by the instability of the power source and the temperature regime of LED chip. Also in the works carried out within the framework of the EURAMET PhotoLED project it was shown that the lowest uncertainty of the results of measurements of photometric parameters (on equipment calibrated by the LED-based standard) is achieved when used as a reference LED with CCT of 4000 K. Based on this concept the reference lamp was created. COB LED manufactured by CREE is placed in an aluminum housing providing primary heat dissipation. Thermostabilization at a temperature of 20 degrees C is provided by a Peltier element and a feedback loop based on the pt-1000 temperature sensor located on the LED surface. Cooling of the Peltier element is performed by a supply fan, while the LED is completely shielded from the effect of air movement. The temperature controller of the LED is located outside the lamp and communicates with it, depending on the required configuration, either through the fittings of the calibrated equipment, or through an optional external cable. This measure reduces greatly the overall dimensions of the source, that allows to apply it in calibrations of photometric spheres with a diameter of 1 m or more. Lamps are equipped with a set of interchangeable connectors that provide compatibility with the power fittings of photometric spheres produced by Instrument Systems GmbH or by using E27 lamp cap. The lamps are powered by an external high-stabilized power source Keithley 2400. The light sources are made in two models: SELFI-I and SELFI-F (acronym for Standard Emitter for Luminous Flux [and luminous] Intensity), as reference lamps of luminous flux and luminous intensity respectively. The SIIP design differs from the SIIS by the presence of a diffuser for creation a uniform luminous flux and a horizontal orientation of the LED. The following was established based on research of metrological characteristics of standard LED lamps: Instability of photometric characteristics during 4 hours of continuous operation is not more than 0.05 %. Instability of photometric characteristics during 500 hours is not more than 0.1 %.