It often takes one single event to interest teenagers in a topic that will become a passion or a career. It is in this spirit that
the SPIE and OSA Student Chapters at Université Laval created the Photonic Games three years ago, to kindle an
interest in teenagers towards studies and careers in optics. The activity, offered each year to more than a hundred grade
11 students, is divided in two parts. First, we offer a hands-on workshop in their classrooms about reflection, refraction,
dispersion, birefringence and polarization. A few days later, all the students come to the Centre d'optique, photonique et
laser (COPL) at Université Laval for a day of competition where a volunteer physics student accompanies each team of
four students. Challenges are various to promote the qualities that make great scientists: creativity, teamwork,
knowledge, inquisitiveness, self-confidence and perseverance. The first two editions of the Photonic Games have proven
to be beneficial for the students, teachers and volunteers, and we endeavor to improve it as we construct on our
experience with the past editions to fine-tune and improve the Photonic Games concept.
KEYWORDS: Light emitting diodes, Lamps, Power supplies, Energy efficiency, Light sources and illumination, LED lighting, Manufacturing, Modulation, Light sources, Solid state lighting
As energy efficiency becomes more and more important, light-emitting diodes (LEDs) are a promising alternative to
traditional lighting. Indeed, the energy efficiency of LEDs is still improving as their luminosity is modulated by current.
Moreover, for applications such as exterior lamp posts, their small size, directionality, colors and high frequency
response allow to combine them and provide design possibilities which are impossible with any other light source.
However, as any lamp, LEDs have a lumen depreciation which is a function of both current and temperature. Thus, to
take advantage of the full characteristics of LEDs, LED luminaire longevity strategies must be carefully studied and
planned, especially since the IES and CIE guidelines state clearly that the luminaire must maintain the rated
recommended light level until the end of the system's operating life. The recommended approach for LED luminaire
specification is therefore to use the end-of-life light level when evaluating the luminaire. Different power supply
strategies have been simulated to determine which one maximizes energy saving and lifetime. With these results, it
appears that active control can save at least 25% in energy, but the best strategy cannot be determined because of
uncertainties in luminosity degradation models.
Since high-power LEDs show great potential in reducing energy consumption worldwide, a great deal of
research has been performed to understand their degradation rate. As reported in many publications, temperature is of
critical importance so lifetests are mainly based on the internal temperature of the junction (Tj). A common testing
method is to overdrive the LED with high current in order to cause self-heating. However, by doing so, it is assumed that
current does not produce self-degradation. This topic is of great importance nowadays because of the recent development
of LEDs used to increase operating current. We have conducted a lifetest on LEDs to isolate the influence of current by
using a thermally-controlled heatsink to keep the same Tj for different driving currents. This paper presents the
experimental setup with the associated protocol used in the experiment. We also present preliminary results obtained
from two high-power white LEDs. These were stressed at currents ranging from 350 mA to 1000 mA and at
temperatures ranging from 75°C to 150°C. To our knowledge, this type of measurement has not been reported in the
literature. In the future, we would like to use a Weibull statistical model to study the combined effects of temperature and
current on the degradation of LEDs.
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