Lighting Knowledge Base & Glossary

Understanding lighting terminology enables informed product selection and effective communication with professionals. This comprehensive knowledge base covers essential terms used throughout the lighting industry.

Light Output and Measurement

Lumen (lm)

The lumen measures total visible light output from a source. Unlike watts (which measure power consumption), lumens quantify actual light production. A standard 60W incandescent bulb produces approximately 800 lumens, while an equivalent LED uses only 8-10 watts.

Candela (cd)

Candela measures luminous intensity in a specific direction. While lumens measure total output, candela describes brightness from a particular viewing angle. Spotlight specifications often use candela to indicate beam intensity.

Lux (lx)

Lux measures illuminance—light falling on a surface. One lux equals one lumen per square meter. Lighting design standards specify required lux levels for different activities: 150 lux for general living areas, 500 lux for reading, and 750+ lux for detailed tasks.

Efficacy (lm/W)

Luminous efficacy measures light output per unit of power consumed, expressed as lumens per watt. Higher efficacy indicates more efficient light sources:

  • Incandescent: 10-17 lm/W
  • CFL: 50-70 lm/W
  • LED: 80-150+ lm/W

Color Quality Metrics

Color Temperature (CCT)

Correlated Color Temperature, measured in Kelvin (K), describes light appearance:

  • 2700K: Warm white, similar to incandescent, relaxing atmosphere
  • 3000K: Soft white, slightly cooler, versatile residential use
  • 4000K: Neutral white, crisp appearance, good for task lighting
  • 5000K-6500K: Cool white/daylight, energizing, excellent color rendering

Color Rendering Index (CRI)

CRI measures how accurately a light source reveals colors compared to natural daylight, rated on a 0-100 scale:

  • 90-100: Excellent color rendering, suitable for color-critical tasks
  • 80-89: Good rendering, acceptable for most residential applications
  • Below 80: Poor rendering, may distort colors noticeably

Color Quality Scale (CQS)

CQS is an alternative to CRI developed by NIST that addresses limitations in how CRI evaluates LED sources. CQS uses more saturated test colors and may better predict color quality for modern light sources.

Electrical Terms

Volt (V)

Voltage measures electrical potential difference. Standard residential voltage is 120V in North America and 230V in Europe. Low-voltage lighting systems operate at 12V or 24V requiring transformers.

Watt (W)

Watts measure power consumption—the rate at which electrical energy is used. With efficient LED lighting, wattage no longer correlates directly with brightness, making lumens the preferred comparison metric.

Ampere (A)

Amperage measures electrical current flow. Circuit breakers are rated in amps (typically 15A or 20A for lighting circuits). Total amperage on a circuit must not exceed breaker ratings.

Driver

An LED driver converts AC line voltage to the DC power required by LEDs, regulating current to protect the light source. Drivers may be integrated into fixtures or external depending on design.

Fixture Types and Components

Downlight/Recessed

Light fixtures installed into ceiling cavities, directing light downward. Available in various sizes (4", 5", 6" diameters common), trim styles, and with different beam spreads.

Troffer

Rectangular light fixtures designed to fit into suspended ceiling grids, typically 2'×2' or 2'×4'. Common in commercial spaces but increasingly used in residential applications.

High-Hat/Can Light

Colloquial terms for recessed downlights, referring to the cylindrical housing installed above ceiling level.

PAR and BR Lamps

PAR (Parabolic Aluminized Reflector) and BR (Bulged Reflector) describe lamp shapes with built-in reflectors. PAR lamps produce focused beams, while BR lamps provide wider flood distribution.

A-Lamp

The classic light bulb shape (Arbitrary designation), commonly used for general lighting in table lamps and fixtures.

Control and Dimming Terms

Triac Dimming

Phase-cut dimming technology that works by chopping portions of the AC waveform. Leading-edge Triac dimmers are most common but may not work well with LEDs.

0-10V Dimming

Analog control protocol where voltage between 0 and 10 volts DC controls light output. Standard for commercial LED fixtures, providing smooth dimming performance.

DALI (Digital Addressable Lighting Interface)

A digital communication protocol for lighting control allowing individual fixture addressing, scene setting, and integration with building management systems.

Daylight Harvesting

Control strategy that dims artificial lighting when natural daylight is available, reducing energy consumption while maintaining target illumination levels.

For practical applications of these terms, explore our technical deep-dive or tools sections.