Applications · Lighting

Lighting Welding: Bulbs, Tubes and Lamps

Lighting manufacturing groups a wide range of joints under one banner: tungsten filament to lead-in wire on incandescent and halogen lamps, cathode and electrode assemblies inside HID and fluorescent tubes, LED bracket leads and heat-slug attach on modern packages, and contact welds inside the metal base. The through-line is refractory-metal handling — tungsten (mp 3422°C), molybdenum (mp 2623°C) and tantalum (mp 3017°C) survive filament operating temperatures but resist fusion, and most joints pair a refractory-metal side against a lower-melting lead-in wire.

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Interior of a clear glass lamp bulb showing a coiled tungsten filament welded to a support electrode inside the bulb, close-up on a dark background

Typical joints

Typical lighting bulb, tube and lamp parts and joints

Lighting product families share a limited palette of joint geometries. Volume assembly and long-lifetime specialty lamps both circulate through the same short list:

Incandescent and halogen filament-to-lead-in joints — tungsten filament coil ends welded to molybdenum or nickel lead-in wires anchored in the stem press
Halogen and HID pinch-seal molybdenum foil joints — thin moly foils carry current through the fused-glass seal, with external and internal lead wires welded to each end of the foil
HID, metal-halide and high-pressure sodium arc-tube electrode assemblies — tungsten electrode rods joined to molybdenum feedthroughs at the ends of the quartz or ceramic arc tube
Fluorescent lamp cathode-to-lead-wire attach — coiled tungsten cathodes welded to nickel lead wires inside the end cap, with an emitter coating baked on after weld
LED bracket, lead-frame and heat-slug attach — package lead ends, heat-slug bonds on chip-on-board substrates and support-bracket welds around the LED die; die-level wire bonding to the die itself is thermo-compression or ultrasonic, an adjacent process scope
Lamp base metal contact welds — E27, E14, B22 and GU10 screw and pin bases with internal contact terminations to the lead wires

Process fit

Which process fits lighting bulb, tube and lamp welding

Resistance spot

Filament-to-lead-in workhorse

Resistance spot handles the bulk of filament-to-lead-in work. Short-pulse energy tacks fine tungsten filament ends onto molybdenum or nickel lead-in wires on incandescent, halogen and HID stems, and also lands fluorescent cathode-to-lead-wire attach cleanly. Volume runs favor this route because a validated parameter window locks in and repeats over long batches on a fixed lamp design, and the concentrated pulse keeps heat away from the glass stem. See the resistance spot line →

Laser

Refractory joints and LED-side welds

Laser earns the difficult refractory joints and most of the LED side of the page. High energy density completes fusion in a pulse short enough to stay ahead of atmospheric oxidation on tungsten and molybdenum, and autogenous seams suit LED bracket leads, heat-slug attach and chip-on-board fixture welds where a filler bead would foul optical or thermal-management geometry. See the laser line →

Pulse arc / Micro TIG

Larger cathodes, prototype, repair

Pulse arc / micro TIG covers larger cathode assemblies, prototype and repair on lamp bodies, and heavier lead-frame terminations on lamp bases. Refractory-metal work needs strong inert shielding — argon at minimum, often an argon-helium blend — or the weld pool oxidizes on approach, so plan the shielding coverage as part of the setup rather than as an afterthought. See the pulse arc line →

Refractory-metal parameter windows do not transfer between alloy grades or between filament and electrode form factors — a sample weld on the actual filament or electrode alloy is the reliable go/no-go before parameter tuning starts.

What’s hard

Common difficulties in lighting bulb, tube and lamp welding

Four difficulties recur across most lighting welding programs, and they are hard in a specific sequence — get the shielding wrong and the other three become moot:

Rapid oxidation of tungsten and molybdenum at weld temperature — both metals oxidize aggressively above roughly 500°C in air, and the oxides that form on molybdenum are volatile at weld temperature so material is lost from the joint surface. Controlled inert shielding, chamber welding, or pulses short enough to stay ahead of oxide formation are the three levers; a bare-air weld on tungsten reads as a scaly gray-brown deposit within seconds.
Dissimilar-metal joints between refractory filament and non-refractory lead-in — the melting-point gap between tungsten (3422°C) and nickel (~1455°C) sits in the 1500–2000°C range, so one side is molten well before the other has warmed through. Asymmetric electrode geometry and a pulse profile that biases heat toward the higher-melting side are needed to reach fusion on both metals within a single pulse.
Thermal shock cracking on tungsten — tungsten is brittle at room temperature and cracks under rapid cooling gradients from the weld peak. Ramped energy profiles, local pre-heat where geometry allows, and controlled cool-down all reduce the temperature excursion the joint has to survive.
Molybdenum foil seal integrity on pinch-glass feedthroughs — the moly foil-to-glass seal is thin and mechanically fragile, and the weld attaching the external lead to the foil has to complete without disturbing the glass bond. Pulse energy stays low and duration stays short, or the glass cracks around the seal and the lamp fails vacuum or fill-gas retention downstream.

Refractory-metal parameter windows shift by alloy grade, electrode formulation and seal geometry, so what locks in on one lamp design rarely transfers straight to the next. Send a sample of the actual filament coil, electrode assembly, moly foil seal or LED substrate — we test-weld it before you commit, and the evaluation costs nothing.

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