Plasma globe

Plasma lamps refer to a type of highly efficient electrodeless lamp energized by radio frequency (RF) power now being introduced to the general lighting market. In the past it has also referred to the novelty plasma lamps which were popular in the 1980s.

The plasma lamp was invented by Nikola Tesla after his experimentation with high frequency currents in an evacuated glass tube for the purpose of studying high voltage phenomena. Modern versions were first designed by Bill Parker. but had no practical use for lighting. The first practical lamp was the sulfur lamps manufactured by Fusion Lighting. This lamp suffered a number of practical problems and did not prosper commercially. These problems have gradually been overcome by manufacturers such as Ceravision and Luxim and only now are High Efficiency Plasma (HEP) lamps being introduced to the general lighting market.

Description

Modern plasma lamps are a family of light sources that generate light by exciting a plasma inside a closed transparent burner or bulb using radio frequency (RF) power. Typically, such lamps use a noble gas or a mixture of these gases and additional materials such as metal halides, sodium, mercury or sulfur. In modern plasma lamps a waveguide is used to constrain and focus the electrical field into the plasma. In operation the gas is ionized and free electrons, accelerated by the electrical field collide with gas and metal atoms. Some electrons circling around the gas and metal atoms are excited by these collisions, bringing them to a higher energy state. When the electron falls back to its original state, it emits a photon, resulting in visible light or ultraviolet radiation depending on the fill materials.

The first commercial plasma lamp was an ultraviolet curing lamp with a bulb filled with argon and mercury vapor developed by Fusion UV. That lamp led Fusion Systems to the development of the sulfur lamp, a bulb filled with argon and sulfur which is bombarded with microwaves through a hollow waveguide. The bulb has to be rotated rapidly to prevent it burning. Fusion Lighting did not prosper commercially, but other manufacturers such as LG Group continue to pursue sulfur lamps.

In the past, the reliability of the technology was limited by the magnetron used to generate the microwaves. Solid state RF generation can be used and gives long lives. However, using solid state chips to generate RF is approximately fifty times more expensive currently than using a magnetron and so only appropriate for high value lighting niches. It has recently been shown by Dipolar [1] of Sweden to be possible to greatly extend the life of magnetrons to over 40,000 hours making low cost plasma lamps possible. Plasma lamps are currently produced by Ceravision and Luxim and in development by Topanga Technologies

Ceravision has introduced a combined lamp and luminaire under the trade name Alvara for use in high bay and street lighting applications. It uses an optically clear quartz waveguide with an integral burner allowing all the light from the plasma to be collected. The small source also allows the luminaire to utilize more than 90% of the available light compared with 55% for typical HID fittings. Ceravision claims the highest luminaire efficacy rating of any light fitting on the market and to have created the first High Efficiency Plasma (HEP) lamp. Ceravision uses a magnetron to generate the required RF power and claim a life of 20,000 hours.

Luxim's LIFI, or light fidelity lamp, claims 120 lumens per RF watt (ie before taking into account electrical losses) . The lamp has been used in Robe lighting's ROBIN 300 Plasma Spot moving headlight. It was also used in a line of, now discontinued, Panasonic rear projection TV..