LED Filaments – A New Technology Enables Classical Design in LED Retrofit Lamps

LpS 2018 - LEDs, OLEDs & Laser Light Sources
26 Sep 2018
14:00-14:30
Seestudio

LED Filaments – A New Technology Enables Classical Design in LED Retrofit Lamps

The technical progress of LEDs in the last years has enabled new luminaire designs in the General lighting market. Due to the increase of efficacy, less LEDs could be used and with the reduced thermal load, heatsink sizes could be minimized or heatsinks could be omitted at all. As a result the luminaires became smaller, thinner and less heavy.
In contrast to the luminaire world, LED retrofit lamps have a strictly defined form factor and there has always been a strong demand to achieve the same appearance as during the last one hundred years. However the first LED retrofit lamps had a quite different look compared to the “good old” incandescent bulbs.  With the increase of LED efficacy, the bulky heatsinks disappeared and the LED bulbs looked more like their classical predecessors. But only with the development and continuous improvement of the LED Filaments, real incandescent look-alikes were possible.
One of the big technical challenges when using LED Filaments, is the thermal design. The main cooling path of an LED Filament lamp is going from the LED directly through the gas filling of the bulb. This requires a good understanding of the thermal situation and sophisticated measurement methods to determine the temperatures of the LED Filaments in the bulb.
Another challenge is the proper electrical driving of the LEDs. The Filaments are switched in different parallel – serial circuit configurations, depending on the input voltage and the targeted lumen output of the lamp. To ensure that the current does not spread inhomogeneously among the Filaments in parallel configurations the forward voltage of the LED Filaments must not differ too much.
The development of LED Filaments is still moving ahead. New upcoming designs allow to omit the usage of the gas filling and thus facilitate the manufacturing processes for LED Filament lamps. Other new developments of LED Filaments are targeted to provide decorative “new” lamp designs, like carbon filament lamps.
Lessons Learned
– A short recap of the history of LED Retrofit lamp development
– Detailed look into LED Filament technology
– Insights in thermal evaluation of LED Filaments in Retrofit bulbs
– Electrical considerations of LED Filaments in Retrofit bulbs
– Outlook on future developments of LED filaments