||Launched in 1991 to coincide with the 100th Anniversary of the company, Philips' QL was the worlds first commercial induction lamp (although for a number of years previously, Matsushita of Japan had marketed the 'Everlight' luminaire which contained a permanently integrated electrodeless fluorescent lamp that could not be removed). Induction lamps offer an exceptionally long service lifetime owing to the fact that no filament or electrodes are used.
The QL system is comprised of three principal elements: the light generating discharge vessel, an antenna to couple power into the lamp, and an HF generator to drive the antenna. The discharge vessel consists of a hollow soft glass bulb, containing a tubular re-entrant portion at the centre such that the antenna can be inserted into the lamp but is not in contact with the lamp's internal atmosphere. The re-entrant is coated with an electron emissive material, while the bulb is coated with a triphosphor fluorescent powder and alumina precoat to reduce blackening from mercury adsorption. The internal atmosphere is a Ne-Ar-Kr mixture and because of the high operating temperature, special amalgams are necessary. One is attached to the re-entrant, and another resides in one of the two exhaust tubes.
This lamp has been made with a partially coated bulb to reveal the internal construction. The auxiliary amalgam flag attached to the re-entrant is shown clearly in the first photo. In the side view of the operating discharge, the shape of the magnetic field produced by the antenna is clearly visualised. Note that there is no discharge in the bulb crown or neck areas where the axial field is relatively weak, and hence the radial electric strength is insufficient to ionise the gas.