Define LED Lighting — What Is LED Lighting?

LED照明是什么

If you specify, buy, or install lighting professionally, you need to define LED lighting more precisely than "an energy-efficient light bulb." LED lighting is an entire system — chip, phosphor, optics, thermal management, and driver electronics — and each of those elements determines whether the product delivers on its datasheet. This guide breaks the system down so you can define LED lighting in specifications, contracts, and tenders with verifiable numbers instead of marketing claims.

How Does LED Lighting Work? The Physics of Electroluminescence

At the heart of every LED is a p–n junction: two layers of semiconductor material, one doped with electron-rich atoms (n-type) and one doped with electron-deficient "holes" (p-type). When forward voltage is applied — typically 2.7–3.5 V for a blue InGaN (indium gallium nitride) chip — electrons and holes recombine at the junction. Each recombination event releases energy as a photon, a process called electroluminescence.

The photon's wavelength — and therefore its color — is determined by the semiconductor's bandgap energy. InGaN chips emit blue light around 450 nm; AlInGaP (aluminum indium gallium phosphide) chips emit red around 620–640 nm. There is no efficient direct-emission white LED. Instead, nearly all white LED lighting uses one of two architectures:

1. Phosphor-converted (PC-LED): A blue InGaN chip is coated with a yellow YAG:Ce phosphor (often blended with red nitride phosphors). Part of the blue light is down-converted to yellow, green, and red wavelengths; the mix appears white. This is the dominant architecture — over 95% of general LED lighting — because it is simple, stable, and efficient.
2. RGB(W) mixing: Separate red, green, blue (and sometimes white) chips are blended by optics and driver control. This allows tunable color but suffers from poorer color rendering and differential aging between chip types, so it is mostly used in entertainment and architectural color-change applications.

Two practical consequences follow from this physics. First, LEDs are inherently directional — the chip emits into a hemisphere (~120° Lambertian pattern), not omnidirectionally like a filament. That is why LED downlights, high bays, and street lights waste far less light in reflectors than legacy sources. Second, LEDs are current-driven, low-voltage DC devices. They cannot connect directly to 230 V AC mains; every LED product includes a driver that rectifies, regulates, and often dims the current. The driver — not the chip — is the most common failure point in LED lighting, which is why driver quality matters more than chip brand when you define LED lighting quality requirements.

Heat: The Silent Performance Killer

Although LEDs run far cooler than incandescent lamps, roughly 55–70% of input power still becomes heat at the junction. Unlike a filament lamp, that heat is not radiated away with the light — it must be conducted through the solder pad, PCB, and heatsink. Every 10 °C rise in junction temperature above the rated point accelerates lumen depreciation and phosphor degradation. A "50,000-hour" LED module operated 20 °C above its rated case temperature may reach L70 (70% of initial lumens) in half that time. When comparing products, always check the rated ambient temperature (ta) and case temperature point (tc) declared per IEC 62031, and demand IES TM-21-21 lifetime projections based on LM-80 chip test data — not a bare marketing number.

Key Data: LED vs. Legacy Light Sources

The vocabulary used throughout this table — luminous flux, efficacy, luminous intensity, illuminance — is formally defined in CIE S 017:2020, the International Lighting Vocabulary. When you define LED lighting terms in a contract, cite CIE S 017 so both parties are bound to the same definitions.

Anatomy of an LED Luminaire: Five Subsystems

To define LED lighting quality, evaluate all five subsystems — a weak link in any one of them degrades the whole product:

1. LED package (chip + phosphor): Determines base efficacy, CRI, and color stability. Common formats: mid-power SMD (2835, 3030) for panels and troffers; high-power ceramic packages for spotlights; COB (chip-on-board) arrays for downlights and track heads.
2. PCB and thermal path: Aluminum MCPCB or ceramic substrates conduct heat to the heatsink. Look for a declared tc point and thermal derating curve.
3. Driver: Converts mains AC to regulated DC current. Key specs: power factor (≥ 0.9 for commercial), THD (< 20%), output ripple (< 5% per IEEE 1789-2015 low-risk criteria), surge protection (2–10 kV for outdoor), and rated lifetime at case temperature (e.g., 100,000 h at tc = 75 °C).
4. Optics: Lenses, reflectors, and diffusers shape the beam. This is where lumens become useful candela distributions — verified by goniophotometer testing per IES LM-79-19.
5. Housing and ingress protection: IP20 for dry indoor, IP65+ for outdoor and washdown, IK08+ impact rating for vandal-prone locations, all tested per IEC 60598-1.

Practical Applications of LED Lighting

Office and Commercial Interiors

LED panels and linear luminaires dominate office lighting because they combine high efficacy (130–160 lm/W system level) with the glare control EN 12464-1:2021 demands — 500 lx maintained on desks, UGR ≤ 19, Ra ≥ 80. Tunable-white LED systems (2700–6500 K) additionally support circadian-aware lighting schemes that shift CCT across the workday.

Industrial and Warehouse

LED high bays replaced 400 W metal halide almost overnight: a 150 W LED high bay delivers the same 20,000+ maintained lumens with instant restrike (metal halide needs 5–15 minutes to re-ignite after a power dip), L90 lumen maintenance at 50,000 hours, and compatibility with occupancy-sensor dimming that discharge lamps could never tolerate.

Retail and Hospitality

COB LED spotlights with CRI ≥ 90 and R9 ≥ 50 render merchandise and food accurately, while narrow-beam optics (10–36°) create the 5:1 accent contrast retail design requires. Because LEDs emit negligible UV and IR, they can light textiles, artwork, and fresh food without fade or heat damage.

Street and Outdoor Lighting

Full-cutoff LED street lights meet EN 13201 and IES RP-8-22 luminance classes at 40–60% lower energy than high-pressure sodium, with better color recognition (Ra ≥ 70 vs. ~25 for HPS). Adaptive midnight dimming — impractical with sodium lamps — adds another 30% saving.

Horticulture, Healthcare, and Special Applications

Because LED spectra can be engineered per application, LED lighting extends beyond illumination: tuned red/blue spectra for plant growth, cyanosis-observation-compliant spectra for hospitals, and UV-free museum lighting for conservation. No legacy source offers this spectral programmability.

How LED Lighting Relates to Other Photometric Terms

You cannot properly define LED lighting performance without the three core photometric quantities, all defined in CIE S 017:2020:

• Lumen (lm) — luminous flux: the total visible light an LED luminaire emits in all directions. This is what IES LM-79-19 measures in an integrating sphere. Divide lumens by input watts to get efficacy (lm/W), the headline efficiency figure for any LED product.
• Candela (cd) — luminous intensity: the flux concentrated in a given direction. LED optics redistribute a fixed lumen budget into candela distributions — a narrow-beam LED spotlight can exceed 5,000 cd from only 600 lm.
• Lux (lx) — illuminance: the flux landing on a surface (1 lx = 1 lm/m²). Standards like EN 12464-1 specify spaces in lux, not lumens — so the ultimate test of an LED installation is measured lux at the task plane, not the fixture datasheet.

The chain is: the LED chip generates lumens, the optic shapes them into candela in useful directions, and the room geometry converts that intensity into lux on the working plane. A complete LED specification addresses all three levels.

Specifying LED Lighting: A 7-Point Checklist

1. System efficacy ≥ 130–150 lm/W (luminaire level, per LM-79 report — not chip-level claims).
2. Lumen maintenance: L80 or L90 at 50,000 h, projected per TM-21 from LM-80 data.
3. Color quality: Ra ≥ 80 general, Ra ≥ 90 + R9 ≥ 50 for retail/medical; chromaticity within ANSI C78.377 bins, Duv ±0.003 across a batch.
4. Flicker: ripple < 5% at 120 Hz per IEEE 1789-2015 for occupied spaces.
5. Driver: PF ≥ 0.9, declared lifetime at tc, appropriate dimming protocol (DALI-2 per IEC 62386 for addressable control).
6. Safety and EMC: IEC 60598-1, IEC 62031, IEC 61547 compliance with test reports.
7. Environment: IP/IK ratings matched to the installation, rated ta covering the real ambient.

Key Takeaways