Measurement of junction temperature of light-emitting diodes in a luminaire

Abstract

There are vast numbers of light-emitting diode (LED) luminaires to choose from, but not all LED luminaires perform reliably. More than half of the input electrical power to a LED luminaire is wasted in the form of heat. Heat management is the one of the most critical issues faced by LED luminaire designers. The long term reliability of a LED luminaire is mainly dependent on the junction temperature of the LEDs. Hence, accurate junction temperature information during luminaire operation is critical for monitoring and assessing the health of the luminaire. In practice, it is extremely difficult to measure the junction temperature of LEDs in modern day luminaires. With the optical system and heat sink surrounding the tiny LED, measurement of junction temperature with direct methods like infrared cameras and thermocouples becomes more complex. This paper explores the possibility of monitoring and measuring the junction temperature of LEDs in a luminaire by making use of the strong correlation between the forward voltage drop at the LED junction and the temperature of that junction. Results of thermal investigations of a LED downlight are presented. The results suggest that the inherent forward voltage/ junction temperature dependency of LEDs can be used to measure and monitor LED junction temperature in a luminaire under operational conditions.

A generalised approach for the estimation of junction temperature and its effect on light output

“…Junction temperature estimation of LED luminaire Efficiency of the LED luminaire ( ¼ P L P E ) for all the drive currents of both the luminaires is computed from the experimental results and is modelled as a linear fit as shown in equation (9). Here, p and q are the coefficients, is efficiency and I d is the LED luminaire drive current.…”

“…7 For the direct temperature measurement and investigation of thermal distribution on the operating LED chip, a nematic liquid crystal thermo-graphic technique was employed. Junction temperature estimation for LED lamp with a forward voltage method at different ambient temperatures is explored by Ke et al 8 and a similar analysis is carried out by Shailesh et al 9 Gu and Narendran. 10 developed a non-contact method for determining the junction temperature of phosphor-converted white LEDs with the help of spectral power density curves.…”

Assessment of methods of marking LED sources with the power of equivalent light bulb

“…The signal then goes to the luxmeter measuring head (10). During laboratory measurements, as a result of the light emitted, this measuring head sends the electrical signal to the luxmeter control unit (11), which is connected to the computer (13) by means of an external power supply (12). The connection of both the meters (luxmeter L100 and power analyzer Norma 4000) to the PC type computer has been effected using the RS-232C serial transmission link.…”

“…Currently, a strong demand has been observed in the field of LED sources which are commonly accepted as excellent replacements of classic light bulbs. Simultaneously with the development of LED sources, considerable interest has been noticeable also in the literature where studies of lighting and electrical parameters of LEDs have been presented, and LED-based applications have been considered [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. From the point of view of the average consumer, the fact of strong marketing conducted by the manufacturers of LEDs, which focuses only on the advantages of these types of light sources, is also notable.…”

Comparative analysis of different cooling fin types for countering LED luminaires' heat problems

“…Temperature plays a significant role in optimizing light output and reliability. High junction temperatures will lead to higher device temperature, which will lead to deterioration of the encapsulate material [4]. It therefore becomes vital to know the operating junction temperature of the LEDs in the luminaire.…”