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On a short to medium term, energy efficient retrofit LED products can offer an attractive solution for traditional lamps
replacement in existing fixtures. To comply with user expectations, LED retrofit lamps should not only have the same
mechanical interface to fit (socket and shape), but also have the similar light effect as the lamps they replace. The
decorative lighting segment shows the best conditions to meet these requirements on short term.
In 2008, Philips Lighting Shanghai started with the development of an LED candle lamp for the replacement of a 15W
Candle shape (B35 E14) incandescent bulb, which is used in e.g. chandeliers. In this decorative application the main
objective is not to generate as much light as possible, but the application requires the lamp to have a comparable look
and, primarily, the same light effect as the incandescent candle lamp. This effect can be described as sparkling light, and
it has to be directed sufficiently downwards (i.e., in the direction of the base of the lamp). These requirements leave very
limited room for optics, electronics, mechanics and thermal design to play with in the small outline of this lamp. The
main voltage AC LED concept is chosen to save the space for driver electronics. However the size of the AC LED is
relatively big, which makes the optical design challenging. Several optical solutions to achieve the required light effect,
to improve the optical efficiency, and to simplify the system are discussed. A novel prismatic lens has been developed
which is capable of transforming the Lambertian light emission from typical high power LEDs into a butter-fly intensity
distribution with the desired sparkling light effect. Thanks to this lens no reflecting chamber is needed, which improves
the optical efficiency up to 70%, while maintaining the compact feature of the original optics. Together with advanced
driver solution and thermal solution, the resulting LED candle lamp operates at 230V, consumes 1.8W, and delivers
about 55 lm at 3000K with the requested radiation pattern and sparkle effect. Some field tests were done with positive
feedback.
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