Lamp types: incandescent, halogen, fluorescent, HID, and LED compared

One-line orientation

Lamp selection trades off four variables — CRI, CCT, efficacy, and lifespan — and the exam tests which lamp type fits which application, which require ballasts, and which pose mercury disposal requirements.

Key points

Five lamp families:

• Incandescent: a tungsten filament produces light by heating to incandescence. It dims easily but creates high heat. It is largely replaced by LED, though it remains useful where instant warm dimming is important.
• Halogen: an incandescent lamp with halogen gas. It runs hotter than standard incandescent and has largely been replaced by LED.
• Fluorescent: an electric discharge creates ultraviolet light, which a phosphor coating converts to visible light. It requires a ballast, contains mercury, and requires regulated disposal.
• HID — Metal Halide: electric arc through metal halide gas. CRI ~85, CCT ~4000 K (neutral white), efficacy 80–100 lm/W, life 10,000–20,000 hrs. Requires ballast. Contains mercury. Long warm-up time (minutes) before full output. Applications: stadiums, gymnasiums, industrial.
• HID — High-Pressure Sodium (HPS): sodium-gas discharge with a long warm-up time and very poor CRI. It suits street and exterior security lighting where color accuracy is unimportant.
• LED: a semiconductor junction converts electricity directly to light. It needs a compatible dimmer and driver heat management. Main trade-offs are higher initial cost and gradual lumen depreciation (L70).

Confusions / comparison

Lamp	CRI	CCT	Efficacy (lm/W)	Life (hrs)	Ballast?	Mercury?
Incandescent	~100	~2500 K	~20	~2,000	No	No
Halogen	~100	~2700–3000 K	15–25 (std); 25–35 (IRC)	~4,000	No	No
Fluorescent	75–85	3000–6500 K	60–90	10,000–15,000	Yes	Yes
Metal Halide (HID)	~85	~4000 K	80–100	10,000–20,000	Yes	Yes
High-Pres. Sodium (HID)	~20	~2000 K	~100	15,000–25,000	Yes	Yes (regulated disposal required)
LED	85+	2700–6500+ K	90–120	50,000–100,000	No	No

Application	Best lamp	Reason
Residential / hospitality ambiance	Incandescent or warm LED	CRI ~100, CCT ~2700 K, easy dimming
Office / general commercial	LED or fluorescent	Efficacy, long life, range of CCT
Retail / art gallery	High-CRI LED (CRI 90+)	Color accuracy for merchandise / artwork
Stadiums / sports facilities	Metal Halide HID or LED	High output, good CRI, large area
Street / parking / security	HPS (legacy) or LED (preferred now)	High efficacy, long life; LED now dominant

Lamp types reduce to four performance patterns

QUALITATIVE MEMORY MAP

Read the same three meters in every panel: efficacy, color rendering, and life

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HPS is the trap: high efficacy and long life do not compensate for very poor color rendering (CRI about 20).

Qualitative grouping for recall; use the card table for exact ranges. Hg families also require a ballast. HID lamps also need time: roughly 1–4 minutes to strike from cold and 2–8 minutes to re-strike once hot, so they suit spaces that stay lit.

Related

→ Lighting: Lighting metrics (CRI/CCT/efficacy definitions) · Illuminance & daylight (how lamp choice affects fc calculation via lumens per lamp) · Lighting controls (dimming compatibility: incandescent/halogen = easy; fluorescent = special ballast; LED = compatible dimmer required).