LED manufacturing and assembling

 

The manufacture of LEDs and LED based products requires specialized measurement technology for the accurate measurement of light intensity, spectral power distribution, color and other quantities. Gigahertz-Optik GmbH offers a comprehensive range of LED light measuring devices, accessories and calibrations. Some example uses of Gigahertz-Optik GmbH products within the field of LED manufacturing and processing follow.

Our sales team will be pleased to support you regarding your particular application requirements. Please contact us via +49 (0) 8193 93700-0 or info@gigahertz-optik.de. 

App. 001

Measuring the effect of temperature on LED performance

Good thermal design of LED light sources and luminaires is essential to ensure optimum LED performance with respect to light output and lifetime. LEDs do not radiate significant amounts of heat but within the LED’s semiconductor junction heat is generated which must be dissipated by convection and conduction. The internal quantum efficiency of LEDs decreases as the junction temperature increases. Junction temperature increases as the current through it is increased. Therefore, the operating junction temperature is determined by the drive current, ambient temperature and the efficiency of the heatsink design.

Lighting manufacturers ensure the quality of their products by measuring photometric and colorimetric parameters such as luminous flux, spectral power distribution, colour temperature and colour rendering.

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This requires precise control of the drive current and temperature stabilisation of the test device during the measurement as detailed in CIE S 025/E:2015 [1]. Most LED lighting products are operated in either constant current mode (Continuous Wave, CW) or some form of PWM, pulse width modulated current mode (Quasi-CW).  However, when specifying or ‘binning’ their products, LED chip manufacturers test their devices in single pulse mode. Therefore, test systems benefit greatly from allowing operation of the LED in both continuous wave and pulse mode, thereby permitting direct comparison of device performance with manufacturers’ claims, for example.

The TP121-TH LED testing system provides fully automated testing routines for SMD and on-board LED devices. The system’s photometric, colorimetric, thermal and electrical measurement parameters all conform to the latest norms and regulations including CIE S 025, IES LM-79-08 [2], and DIN 5032 Part 9 [3].


References

[1] CIE S 025/E:2015 Test Method for LED lamps, LED luminaires and LED Modules

[2] IES LM-79-08 Electrical and Photometric Measurements of Solid-State Lighting Products

[3] DIN 5032-9 Photometry - Part 9: Measurement of the photometric quantities of incoherent emitting semiconductor light sources

App. 002

Luminous flux and color measurement of board mounted LEDs

Manufacturers offer LEDs sorted or ‘binned’ according to their Correlated Color Temperatures (CCT), lumen output, and forward voltage parameters. For example, standards such as ANSI C78.377-2017 [1] specify the range of chromaticity values recommended for general lighting in terms of ‘bins’ that are defined by a series of chromaticity quadrangles plotted along the black body locus in the CIE 1931 color space.

Although this pre-sorting limits tolerance ranges, it does not release the user from metrological quality control. This is mainly due to the fact that the operating parameters used for LED binning do not match those of the end application.

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Manufacturers typically specify bins for their devices based on measurements using ~20 ms current pulse operation and with a junction temperature of 25°C. Therefore, in addition to the particular current drive conditions employed, the thermal design of the LED carrier board and associated heatsink can significantly influence the optical performance of any assembled LED module or product.

The two possible measures of the light intensity of assembled LEDs are luminous flux (lm) and luminous intensity (cd). The measurement of the luminous flux is preferable to the measurement of the luminous intensity, since no particular alignment of the measuring device with the beam of the LED is necessary. The BTS256-LED tester incorporates an integrating sphere in conjunction with its BiTecSensor technology enabling the direct measurement of the luminous flux, spectral power distribution, CCT and color rendering (CIE CRI and IES TM-30-15) of in-situ LEDs. The cone-shaped measuring aperture of the integrating sphere is simply positioned over the assembled LED for measurement.


References

[1] Specifications for the Chromaticity of Solid State Lighting Products, ANSI C78.377-2017

App. 003

Spectroradiometer requirements for LED Binning

Despite the most sophisticated manufacturing technologies employed by the semiconductor industry, light output and colour temperature of LEDs varies from chip to chip. Therefore, binning is employed to maximise yields and to categorise products. Standards such as ANSI C78.377-2017 [1] define tolerance bands or ‘bins’ with respect to chromaticity boundaries. Therefore, without exception, LED binning requires the absolute spectral power distribution of devices to be measured in order to precisely determine the light output and the correlated colour temperature (CCT) of each individual LED. Light output is most commonly measured in terms of luminous flux (lm) although Averaged LED Intensity [2] is also sometimes specified.

LEDs are mass produced necessitating the shortest possible measuring times for binning purposes.

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Manufacturers test their devices using a single pulse with typical durations of around 20 ms or less. This high speed testing places great demands on the spectroradiometer requiring high light throughput of the input optics, high sensitivity and the smallest possible dark signal as well as fast data processing and data transmission. Additionally, the software must provide for easy integration of the measuring device into complete automated systems. With the BTS2048-VL spectroradiometer and its measurement accessories for luminous flux and Averaged LED Intensity, Gigahertz-Optik GmbH offers a high-performance measuring device for LED binning.


References

[1] Specifications for the Chromaticity of Solid State Lighting Products, ANSI C78.377-2017

[2] CIE 127:2007 Measurement of LEDs

App. 004

Quality control of LED spotlight manufacturing processes with a single measuring device

The development and manufacture of good quality LED spotlights requires an extensive range of photometric and colorimetric measurements. The investment required for equipping and operating a comprehensive photometric test laboratory can seem prohibitive for the many medium-sized manufacturers offering products in this marketplace. Therefore, the possibility of a universally applicable and compact measuring device for the various measurement tasks is attractive.

The optical parameters that are required to be measured in the development and production processes of LED spotlights include:

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  • Luminous flux and chromaticity including CCT of the LED
  • Luminous flux and chromaticity including CCT of the LEDs assembled on PCBs
  • Luminous flux and chromaticity including CCT of the LED with optics
  • Luminous intensity
  • Luminous intensity spatial distribution

These photometric and colorimetric measures require a selection of input optics configured with a suitably calibrated spectroradiometer. With the BTS256-LED Plus Concept Gigahertz-Optik GmbH offers an affordable spectroradiometer with accessories for all of the above listed measurement tasks.