No abstract

High-power LEDs with high luminous efficacies, compact sizes, long lifetimes and a wide colour range, are rapidly taking the place of conventional light sources in general lighting applications. But these properties of high-power LEDs are dependent on temperature and driving current. In this study, 24 samples of commercially available, high-power, white LEDs were measurement for their electrical, optical and thermal characteristics as well as their efficiency, luminous flux, luminous efficacy, correlated colour temperature and colour rendering index over six temperature steps at three different driving currents. LED manufacturers' catalogues including such information will allow consistency between the design and application stages of an installation. Also, it will make the technical and economic optimization of luminaires using high-power LEDs easier.

The increase in the LED junction temperature is an important problem since it directly affects the lumen output and the colour characteristics of the LED chips, resulting in low performance in LED-based lighting systems. In this study, commercial computational fluid dynamics software is used with the JEDEC's tworesistor compact thermal model to analyse the temperature distribution in two selected luminaires. It is aimed to show that use of the two-resistor model and measurement combination is a fast and easy way of predicting thermal behaviour of the system and LED junction temperatures instead of trial and error designs and thus ensures a better estimation for the total luminous flux of the luminaire and lowers the costs and time required for the prototyping processes.

This study investigates visibility levels for different road lighting scenarios. Four different road lighting classes (M2, M3, M4, M5), two different colour temperature luminaires (4000 K and 6000 K) and four different critical object reflectances (0.20, 0.30, 0.40, 0.50) were used to determine the effects of lighting classes and colour temperatures on the critical object detection. In total, 1920 photographs were taken on a test road and visibility levels were calculated for each case. From these 1920 visibility levels, photographs corresponding to 245 visibility level values ranging from 1 to 9 were selected and evaluated by 30 subjects aged between 25 and 35 years in a laboratory environment. As a result of the study, it was shown that visibility levels are between 7.0 and 8.5 for road lighting classes ranging from M2 to M5, illuminated by light sources with different colour temperatures, for 100% detection of critical objects. This result is in line with the suggested VL values changing between 7 and 10 in the literature.

As the equipment is improving, the luminous efficacy of Chip on Board (COB) LEDs are increasing. In this study, the utilization of COB LEDs in an industrial high-bay luminaire, which can be considered as a relatively high power application, has been investigated starting from the initial design process. For an industrial hall, single-chip LED based reference luminaires, which can provide the required lighting quality criteria have been identified. COB LED selection and photometric measurements are done, and the number of COB LEDs to be used has been calculated by targeting the luminous flux value of reference luminaires. The COB LED based luminaire prototype with a plate finned heat sink was modelled by using a CAD software and the computer aided thermal simulations were performed. Then the prototype was manufactured and experimentally analysed. The highest difference between the experimental analysis and the thermal simulation was found to be less than 7 %, which demonstrates the consistency of design and analyses. This study is an example of the steps to be followed in the manufacturing stage of a COB LED based luminaire. Additionally, it is aimed to provide a perspective to the use of COB LEDs in high power applications.