Incandescent / Halogen Lamp
Lamp
A tungsten filament heated white-hot by current — the original electric light. Beautiful colour rendering and dimming, terrible efficiency (~95% of the power leaves as heat). Halogen versions run hotter and last longer via the halogen recycling cycle.
Schematic symbol
Lamp
How incandescent / halogen lamp appears in a circuit diagram.
Types & variants
Key specs
Wattage
WPower drawn — 40/60/100 W GLS classics. Light output is only ~10–15 lm/W.
Voltage
V230 V mains types, or 12 V halogen (MR16) needing a transformer/driver.
Base/cap
—B22 bayonet (India standard), E27/E14 screw, GU10 twist, G4/G9 pins, R7s ends.
Colour temperature
K~2700 K warm white; halogen ~3000 K. CRI is a perfect 100 — the benchmark other lamps chase.
Lifespan
hours~1000 h for GLS, 2000–4000 h halogen. Filaments usually fail at switch-on inrush.
Markings
Wattage, voltage and cap type stamped on the glass or cap, e.g. '230V 60W B22'. Halogen capsules mark voltage and wattage on the pinch seal.
Standard values
GLS: 25/40/60/100 W in B22/E27. Halogen: 20/35/50 W MR16 & GU10, 150/500 W R7s linear, 10–40 W G4/G9 capsules.
How to choose
For almost all lighting, choose LED instead. Incandescent/halogen still earns its place for: perfect CRI display lighting, oven and appliance bulbs (LEDs die in the heat), rough-service and heat lamps (poultry brooders), and dimmer-heavy vintage fixtures. Never touch a halogen capsule with bare fingers — skin oil creates a hot spot that bursts the quartz.
Pinout & package
Two filament terminals through the cap. Bayonet caps contact via two bottom pads; screw caps use the shell and centre pad; capsule types use two pins directly.
Example circuits
- Series bulb as a current limiter for safely powering up repaired mains equipment (the 'dim bulb tester')
- 12 V halogen with an electronic transformer
- Filament bulb as a self-regulating soft-start resistor (classic amplifier trick)
- Heat lamp in a brooder or food warmer
Common failures
Filament fatigue and break (open circuit, often with a flash at switch-on), blackened bulb from tungsten evaporation, loose cap cement, and halogen capsules bursting from fingerprints or overvoltage.
How to test
Continuity across the cap contacts: a good filament reads tens of ohms cold (a 60 W/230 V lamp ~65 Ω cold, rising ~10× when hot). Open circuit = dead lamp. Visual check: broken or sagging filament, dark glass.
Substitutes
LED retrofit lamps with the same cap replace nearly all of them (a 9 W LED ≈ 60 W GLS). For dimmers, use dimmable LEDs matched to the dimmer type. Keep true incandescent only for heat-dependent or extreme-temperature uses.