Before LEDs dominated specifications, four light sources ruled. Each had a job. LED replaced most, but not all. Knowing what came before makes you read modern spec sheets sharper.
Four ideas to carry into the next specification conversation you have.
A tungsten filament in a high-pressure inert fill with a trace of halogen, sealed in quartz. 9 to 21 lm/W bare lamp, 1,000 to 5,000 h. Regulation ended it, not efficacy alone.
A low-pressure mercury arc puts about two-thirds of its power into invisible 254 nm ultraviolet, which a phosphor converts. 69 to 104 lm/W bare lamp by lamp type. Being phased out of manufacture and trade under the Minamata Convention.
Metal halide 73 to 112 lm/W, high-pressure sodium 91 to 137 lm/W, both bare lamp and both strongly wattage-dependent. Metal halide lost on warm-up, restrike and maintained output; sodium lost on colour.
LED has not replaced germicidal UV-C, infrared process heating, or tungsten as a photometric transfer standard. Pre-LED tech still ships, and for good reasons.
Bare-lamp values for late-generation pre-LED products against modern LED equivalents. Lamp lm/W are initial bare-lamp figures at 100 h and 25 °C on reference gear; system efficacy with control gear is lower. Lamp life is hours to 50% failures and depends on the switching cycle, while LED life is L70 lumen maintenance. The two columns are not on the same basis.
| Source | Typical efficacy · life | LED replacement |
|---|---|---|
| Incandescent (60 W, 120 V) | 14 lm/W · 1,000 h | LED A-lamp, roughly 7× the efficacy |
| Halogen (mains and capsule) | 9-21 lm/W · 1,000-5,000 h | LED MR16 88 lm/W bare lamp · L70 40,000 h |
| Compact fluorescent (CFL) | 40-67 lm/W · 6,000-13,000 h | LED A-lamp, roughly 1.5× the efficacy |
| Linear fluorescent (T12 to T5) | 69-104 lm/W · 15,000 h+ | LED T8 lamp 130 lm/W and 1,600 lm (DLC SSL V6.0) · L70 50,000 h |
| Mercury vapour HID | 50-55 lm/W · 24,000 h | LED high bay 135-150 lm/W luminaire · L70 80,000 h |
| Metal halide HID | 73-112 lm/W · 15,000-20,000 h | LED high bay 135-150 lm/W luminaire |
| High-pressure sodium | 91-137 lm/W by wattage · 24,000-40,000 h | LED street luminaire 125-141 lm/W |
| Low-pressure sodium (not HID) | 176 lm/W monochromatic · 18,000 h | Narrow-band amber LED, 585-605 nm |
Five points that help you read retrofit jobs correctly.
A halogen lamp cools as it dims because the filament itself cools, and its colour temperature follows supply voltage as V0.37. From 3000 K that is roughly 2700 K at 40% light output and about 2300 K at 10%. Efficacy collapses with it, to around 30% of rated at 10% output. Most LEDs hold their CCT instead, so warm-dim products are engineered to imitate the curve, typically 2700 K down to 2200 K.
The three types are defined in UL 1993. Type A runs on the luminaire's existing electronic fluorescent ballast: it will not work on a magnetic one, and the surviving ballast costs about 20% of rated efficiency. Type B bypasses the ballast and wires mains to the lampholders: it requires electrical modification, the correct wiring configuration and a permanent retrofit label, and GSA's 2024 P100 barred it outright, though that standard was rescinded in February 2025 and its replacement carries no equivalent prohibition. Type C fits an external LED driver in place of the ballast: the most installation work, but a purpose-designed LED system with no fluorescent-ballast compatibility to worry about. Survey the existing ballasts before you price a Type A rollout: a dimming ballast with a non-dimming lamp destroys the ballast.
How long depends on the lamp. A protected pulse-start metal halide reaches 90% brightness in about 3 minutes and restrikes hot in 2 to 4; a standard switch-start lamp takes around 15 minutes to restrike, and a 1500 W stadium lamp 10 to 15. Always ask which output threshold a quoted figure refers to. Stadiums kept HID late because dark periods during play are not tolerable, and LED took the sector once instant restrike made the argument moot.
Saudi Arabia acceded to the Minamata Convention on 27 February 2019, never signing or ratifying it, and it entered into force for the Kingdom on 28 May 2019. The Kingdom made no declaration under Article 30(5), so annex amendments apply through the Convention's default Article 27 mechanism unless a timely notice of non-acceptance is submitted; state the relevant amendment and its effective date. The Convention restricts manufacture, import and export after a phase-out date, not use, and its lamp dates are 2020, 2025, 2026 and 2027 by lamp type and mercury dose. Retrofit projects still have to plan hazardous-waste handling under the Waste Management Law (Royal Decree M/3, 2021), which governs hazardous waste generically without naming lamps.
Observatory towns once specified low-pressure sodium because nearly all its output sits in the sodium doublet near 589 nm, a single band that can be notched out of telescope data. That era has closed: sodium is out of production and dark-sky practice has moved to narrow-band amber LED. Tucson and Pima County's proposed 2025 draft code defines it by peak wavelength (585 to 605 nm) and a full width at half maximum below 18 nm; both jurisdictions still enforce their 2012 code, so a low CCT alone is not evidence of compliance. Reptile husbandry still specifies UV-B fluorescent. A 2024 Zoo Biology survey of 18 UVB-LED lamps found all had little similarity to the solar UV spectrum, every one lacking output in the 315 to 335 nm band the authors call essential to the natural self-regulation of cutaneous vitamin D3 synthesis. Those lamps were sampled before the study was submitted in January 2023, so the finding does not describe models released since. "Just put LED" is not always the right answer.
From halogen wall-wash to HID high bay to T8 retrofit, we audit existing installations and specify the LED equivalent against illuminance, distribution, colour and dim behaviour on the task plane, not against the old lamp's lumens.
Every figure on this page traces to a primary document. Standards are cited in their current active revisions; lamp figures come from the manufacturer's own datasheet for a named order code.
Every numbered citation the carousel carries, in order. Standards are cited in their current active revisions; lamp figures come from the manufacturer's datasheet for a named order code. Data checked 24 August 2026.
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