Hot cathode fluorescent lamp

A hot-cathode fluorescent lamp, comprising:

• a glass bulb;
• a pair of filament coils disposed in respective ends of the glass bulb, each filament coil having a coiled portion coated with an electron emissive material;
• a pair of feeder members through which electric power is supplied to the respective filament coils;
• and
• a heat-resistant sleeve disposed to cover one of the coiled
• portions, wherein
• a winding axis of each coiled portion is substantially parallel to a tube axis of the glass bulb,
• the heat-resistant sleeve includes (i) a tubular conductive body having open ends and supported by one of the feeder members, and (ii) an insulating film attached to an inner circumferential surface of the conductive body, and
• the insulating film is thicker at a region corresponding to where a potential difference between the conductive body and the coiled portion occurring upon voltage application is larger than at a region corresponding to where the potential difference is smaller, with respect to regions where a distance between the conductive body and the coiled portion is shortest.

A hot-cathode fluorescent lamp, comprising:

• a glass bulb;
• a pair of filament coils disposed in respective ends of the glass bulb, each filament coil having a coiled portion coated with an electron emissive material and a first lead portion and a second lead portion each extending from respective ends of the coiled portion toward a closer one of the ends of the glass bulb;
• and
• a heat-resistant sleeve disposed to cover one of the coiled portions, wherein
• a winding axis of each coiled portion is substantially parallel to a tube axis of the glass bulb,
• the heat-resistant sleeve includes (i) a tubular conductive body having open ends, and (ii) an insulating film attached to an inner circumferential surface of the conductive body,
• the first and second lead portions of said one of the filament coil extend beyond one of the open ends of the sleeve adjacent the closer end of the glass bulb, and
• the insulating film is thicker at a region axially closer to the closer end of the glass bulb than at a region further away from the closer end of the glass bulb.

A hot-cathode fluorescent lamp, comprising:

• a glass bulb;
• a pair of filament coils disposed in respective ends of the glass bulb and having a coiled portion coated with an electron emissive material and a pair of led portions extending from respective ends of the coiled portion,
• a pair of feeder members through which electric power is supplied to the respective filament coils;
• a heat-resistant sleeve disposed to cover a corresponding one of the coiled portions;
• and
• a sleeve lead extending from the conductive body in a direction axially of the sleeve and connected to one of the feeder members, wherein
• a winding axis of each coiled portion is substantially parallel to a tube axis of the glass bulb,
• the heat-resistant sleeve is supported by said one of the feeder members via the sleeve lead and includes (i) a tubular conductive body having open ends, and (ii) an insulating film attached to an inner circumferential surface of the conductive body, and
• the insulating film is thicker at a region circumferentially closer to the sleeve lead than at a region circumferentially further away from the sleeve lead.