Discharge lamp, particularly cold-start fluorescent lamp, and method of its manufacture

US5614784A · kind A · utility

Assignee

• Patent-Treuhand-Gesellschaft fur elektrische Gluhlampen mbH · DE

Inventors

• Christian Harzig · Mering, DE
• Roland Hoffmann · Augsburg, DE
• Erolf Weinhardt · Diedorf, DE

Key dates

• Filing date: Jun 15, 1995
• Grant date: Mar 25, 1997
• Expiry date: Jun 15, 2015

Classification

• Technology area (CPC H): Electricity
• CPC primary: H01J9/042
• WIPO field: Electrical machinery, apparatus, energy
• WIPO sector: Electrical engineering

Abstract

The lifetime of cold-start fluorescent lamps is increased, and the ability to withstand repeated ON-OFF switching cycles enhanced by coating the electrodes with an emitter which consists of barium oxide and a small portion of metallic barium and, optionally, up to 20 mol-% of strontium oxide and a small portion of metallic strontium, preferably only up to about 5 mol-% of strontium oxide--metallic strontium. To make the emitter, barium carbonate, optionally mixed with strontium carbonate, is applied in paste form to the electrodes which, when coated, are introduced into an envelope and sealed therein. The envelope is then evacuated, and the electrodes are heated, thus converting the barium carbonate to barium oxide and metallic barium, and the strontium carbonate, if present, to strontium oxide and metallic strontium, so that the electrodes will be coated with barium oxide, optionally strontium oxide, and metallic barium and optionally metallic strontium. The evacuation and activating step can be carried out essentially simultaneously, by evacuating the envelope through a pump tube and heating the electrodes to above about 800.degree. C. by passing a current pulse therethrough.