QUALITY ASSURANCE AT SEGULA

the Ulbricht sphere

IN-HOUSE QUALITY ASSURANCE AT SEGULA

At SEGULA, we place the utmost importance on the quality of our LED light sources. True to the motto ‘Trust is good, control is better’, all LED light sources that arrive at our premises undergo strict and meticulous quality control. This is regardless of the supplier or any existing tests and reports. That is what quality assurance means at SEGULA!

As well as visual inspection – which involves assessing factors such as the quality of the glass, weight and size – we have our own small lighting laboratory where we put every single light source, no matter how small, through its paces. To do this, we use what is known as an integrating sphere. In this article, we explain what this is and how it works. 

THE ULBRICHT SPHERE

The integrating sphere, or spherical photometer, is used to measure the luminous flux of an unknown light source. It is a hollow sphere painted in pure white with a matt finish and can have a diameter ranging from half a metre to five metres. For our purposes, it has a diameter of 1.20 metres. A light source, in our case an LED light source, is placed inside. The white inner surface ensures that every surface element is illuminated with equal intensity. Multiple reflections thus fill the interior of the integrating sphere with a uniform, diffuse light field. This results in a combination of direct and indirect luminous flux. A portion is absorbed and dissipated as heat. After switching on the light source, the intensity increases until the absorbed luminous flux equals that emitted by the light source.

FUNCTION OF THE ULBIRCH SPHERE

A photometer is mounted on the inside of the sphere, which measures only the diffuse, indirect illumination. It is shielded from direct light by a baffle. The Ulbricht sphere serves to collect the luminous flux from all directions and convert it into a simple, measurable illuminance. This is usually expressed in lux, but the photometer can be set to immediately display the required luminous flux in lumens.

And it is not only lumens that can be measured, but also other parameters relevant to LED light sources. These include, for example, the chromaticity, the spectrum and also the color temperature. 

The sphere is always just one part of a measurement setup. This also includes the photometer, various transformers and, of course, the evaluation devices, such as a display and specific software on the connected PC.

SET-UP AND CALIBRATION

This entire system is calibrated in advance. This is done using a light source whose spectral distribution and luminous flux values are known. These values then serve as a reference for all subsequent measurements. To avoid deviations and measurement errors, recalibration is carried out at regular intervals. This is because external influences, such as temperature fluctuations, humidity and dust, can alter the properties of the coating over time. 

Every product at SEGULA undergoes a thorough in-house inspection to guarantee consistently high quality and to immediately identify, document and communicate any deviations.

LONG-TERM TESTING

And it is not just these ‘short-term measurements’ that form part of our quality control. We also carry out internal long-term tests. The various types of filament are left to ‘hang’ for several weeks and months in a test room set up specifically for this purpose. ‘Dry-aged bulbs’, so to speak. 

This allows us to closely observe and document how SEGULA LEDs behave or change during continuous operation under normal conditions.