Family: Technology
Incandescent bulbs
Overview
Incandescent bulbs produce light by thermal radiation. Electric current meets resistance in a thin tungsten filament, heating it to roughly 2,500-3,000 kelvin until it glows and emits visible light along with substantial infrared. The filament sits in a glass envelope filled with inert gas or held under vacuum to slow evaporation. Because emission follows the physics of a hot body, the light is a smooth continuous spectrum set almost entirely by temperature. This mechanism is simple and well understood, but it is inherently tied to heating the filament, which shapes efficiency, colour and lifespan discussed in the rows that follow.
Production method
- How light is produced
Thermal radiation from a wire filament heated by resistance until it glows.
More detail
Incandescent bulbs produce light by thermal radiation. Electric current meets resistance in a thin tungsten filament, heating it to roughly 2,500-3,000 kelvin until it glows and emits visible light along with substantial infrared. The filament sits in a glass envelope filled with inert gas or held under vacuum to slow evaporation. Because emission follows the physics of a hot body, the light is a smooth continuous spectrum set almost entirely by temperature. This mechanism is simple and well understood, but it is inherently tied to heating the filament, which shapes efficiency, colour and lifespan discussed in the rows that follow.
Quality indicators
- Energy efficiency
Roughly 10-15 lumens per watt; the large majority of energy becomes heat.
More detail
Incandescent bulbs are generally characterised by energy agencies as low-efficiency light sources, typically delivering only around 10 to 15 lumens per watt. The large majority of the electrical energy becomes heat rather than visible light, a direct consequence of the thermal-radiation mechanism. Because of this low efficacy, several jurisdictions have restricted or phased out general-service incandescent lamps through efficiency regulations. Exact figures depend on wattage and design, and specialised or rough-service types differ. The physics that gives incandescent light its continuous spectrum is the same physics that limits its efficiency, so improvements within the technology are inherently constrained.
Qualitative characteristics
- Heat output
High radiant and conductive heat; surface can reach burn-hazard temperatures.
More detail
Incandescent bulbs release most of their input energy as heat, both as infrared radiation and as conduction through the glass, since heating the filament is how they make light. Surface temperatures can become high enough to pose burn or fire risks near flammable materials, and this is reflected in safety guidance. The same waste heat has occasionally been used deliberately, for example in small heat lamps or older enclosed appliances. In normal lighting use, however, this heat represents the energy that does not become visible light. The strong thermal output is a direct, unavoidable feature of the incandescent mechanism rather than a design flaw that can be tuned away.
Health-related indicators
- Light and the body
The recommendations are expressed not in lamp types but in the spectrum and level of light at the eye
More detail
Light affects circadian rhythms and sleep, and through them well-being and performance. The consensus lighting recommendations are formulated not in the names of technologies but in a measurable quantity — melanopic equivalent daylight illuminance under an international standard. The question is therefore settled by the spectrum and level of light at the eye, not by whether the lamp is incandescent.
Consumer experience
- Cost over time
Low purchase price, higher energy use; total cost depends on hours and rates.
More detail
Incandescent bulbs typically have the lowest purchase price, which can make them appear cheaper at the point of sale. Over time, however, their low efficiency raises electricity use and their short rated life means more frequent replacement, both of which add to the total cost of ownership. How large that running cost becomes depends heavily on usage hours, local electricity prices and how the lamp is operated, so comparisons vary between households and countries. Some specialised or infrequently used applications may see little difference. Because the outcome is so context-dependent, reliable universal cost figures are limited, and estimates should be read as scenario-based.
Regulatory notes
- Market access and efficiency rules
Withdrawn from the European market by regulation; the process is traced from 2000 to 2020
More detail
The incandescent lamp is a rare case of a category leaving the market not by the buyer's choice but by a regulator's decision. A study traces this phase-out in Europe after the ban entered into force, from 2000 to 2020, and examines the processes that accompanied it. This concerns the European market: elsewhere the timing and scope of such measures differ.
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Common comparisons
Sources and evidence
Sources by kind of evidence
AGENCYAgency2
REVIEWSystematic review2
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