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Wednesday, August 12, 2009

Ceravision : Using microwaves to produce light

Earlier this week Ban The Bulb visited an innovation centre at Bletchley Park to meet the team behind a company called Ceravision that has developed a revolutionary lighting technology, which could replace traditional incandescents light bulbs, halogens, fluorescents, high intensity discharge lamps and LEDs over the years ahead.

Their ingenious electrodeless, plasma lamp technology uses carefully contained and focused microwaves to heat special blends of gas in a way that efficiently produces a full spectrum of bright and controllable light (equivalent to 70W - 5000 W incandescents) without producing excess heat or using mercury.

Ceravision's technology consists of the following components:

a magnetron which emits microwave energy,

a transparent quartz resonator which concentrates the microwave energy in a small volume,

a plasma space (molded within the one-piece resonator) which contains a mixture of gas and metal halides.

an antenna which delivers the microwave energy into the resonator, causing an electric field to ionise the gas plasma, which vaporises and combines with the metal halides to produce light.

In the past, people have tried using microwaves to heat gases in large glass bulbs. However, this technology is different, and represents a major step forward, because it uses a solid block, known as resonator, to shorten the wavelengths of the radio frequencies and heat gases within a far smaller volume.

Initially, Ceravision used opaque discs of ceramic to focus microwaves on a small glass bulb containing gas embedded within the ceramic disc. This approach succeeded in providing a bright point source of light, but the opaque block of ceramic prevented most of the light produced by the glass bulb, embedded within the resonator, from being emitted.

Ceravision have therefore changed their original design by patenting the use of a transparent quartz resonator, which allows more of the light produced by the glass bulb to be emitted.

Fortunately, the microwaves needed to make this device work are safely trapped within the resonator by a simple metal mesh, which acts as a Faraday Cage.

As a result of this well understood containment process, the microwaves are radiated into the bulb via the antenna, which lies next to the glass bulb at the centre of the resonator, and can be used to create an illuminating gas plasma inside the glass bulb.

Using this technology it is already possible to replace High Intensity Discharge (HID) lamps and new small source lamps (such as car headlights and projector lamps), UV lamps and domestic lamps are under development - with new designs that are 2+ x more energy efficient, 2x - 25x longer lived and affordable.

Ceravision's electrodeless microwave driven lamp system is extremely exciting because it offers better colour rendering and dimming than both compact flourescent lamps and high intensity discharge lamps, and has fewer problems with excess heat production than incandescents and LEDs.

It simply remains to be seen how well the energy performance and purchase price of domestic versions of Ceravision's technology will compare to the competing technologies, but it is definitely a very positive development that the EU's ban of traditional incandescents has allowed radically new lighting technologies, such as this, to come to market.

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 microgramme 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 Ceravision to deliver the world's first mercury-free High Intensity Discharge lamp that can deliver white light of exceptional purity (a Colour 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.

The burner is made of low hydroxyl quartz glass and contains no metal wires or metal electrodes. This allows the light formation from the plasma process to continue without contamination of the burner contents by metal wires or electrodes modifying the internal chemistry. This simplicity of construction maintains an unprecedented purity of materials within the burner during its continuing operation and allows the lighting platform to offer designers excellent colour constancy and lumen maintenance over an extended operating lifetime.

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