Microwave Journal

Update on RF-driven Plasma Lighting

July 8, 2009

Ceravision Ltd is a leading innovator in the field of ultra-efficient, RF-driven plasma lighting. Ceravision's revolutionary lamp system has been developed for use in a broad range of applications, using either solid state or magnetron- based RF power sources operating at 2.4 GHz. The Ceravision system can be scaled from 70 watts to 5 kilowatts and outperforms and replaces incumbent technology in a number of fields including warehouse lighting, street lighting and stadium lighting. According to Ceravision's website, the microwave light has an efficiency of more than 50 percent, compared with fluorescent tubes' efficiency of about 15% and traditional light bulbs, which emit only about 5 percent of their energy conversion as light, the vast majority being emitted in the form of heat.

How it Works
Microwave energy at a frequency of 2.4 GHz is focused into a small transparent glass ampoule (called a Burner) containing a noble gas at low pressure and micro-gram quantities of selected metal halide salts. The microwave energy focused into the waveguide containing the burner forms an electric field ionizing the noble gas molecules to rapidly form a gas plasma within the glass ampoule, the plasma begins to vaporize the metal halide salts present. The plasma and metal halide salts combine to emit light, this technique provides the ability to produce a broad spectral emission using simple chemical compounds. This molecular excitation is a unique feature of the technology and allows the company to deliver the world's first mercury-free High Intensity Discharge lamp that can deliver white light of exceptional purity (a Color Rendering Index (CRI) measurement of 97 being achievable), and which also meets all current and projected regulations for control of radio frequency emission from any part of the system.

One of the breakthroughs claimed by Ceravision is the ability to prevent high levels of microwave power being reflected back to the source and damaging it at switch on. The microwave interface unit limits the amount reflected back to less than 0.5 percent of incident microwave power, the company said. Instead the output is launched via a metal antenna into a metal-coated low-loss dielectric resonator. The mechanical dimensions of the resonator determine the ultimate performance of the lamp system and where the microwave energy will be focused. At the focal point the resonator has a cavity into which the electrode-less "burner" is inserted.

Ceravision's original innovation utilizes focused microwave energy to excite the burner. The microwave energy produced is fully contained within a dielectric waveguide made from ceramic or similar materials. The waveguide itself is compact and is available in numerous configurations. When the lamp is operating the R-EFF™ microwave interface unit allows microwave energy from the power amplifier to pass into the waveguide and burner assembly, but prevents reflected microwave energy from bouncing back from the waveguide towards the amplifier. This patented component is unique to Ceravision products, and allows high-reliability, long-life systems to be built at low material costs. Using the R-EFF interface unit with the Waveguide and Burner assembly, there is no need for any expensive and complicated electronic circuitry to continually monitor and adjust the RF microwave power source operating characteristics. The R-EFF allows any solid state derived power source to operate in a phase locked spot frequency mode in either a continuous wave or modulated form.

The Microwave Power Source The Ceravision lighting system can use a wide variety of simple, low-cost microwave power sources. Ceravision currently uses a range of microwave power sources comprises designs with various microwave technologies to deliver power at different levels and costs.

Current designs include:
Gallium Arsenide microwave power transistors between 50W and 400W
Gallium Nitride microwave power transistors between 50W and 400W
LDMos Silicon microwave power transistors between 50W and 400W
Magnetron microwave power tubes between 100W and 5KW

The choice of microwave power technology is determined by customer requirements in power level, mechanical size constraints, operating lifetime and system cost for their specific application.