Colour and appearance
CDL — Cool Daylight
A common Indian retail abbreviation for a cool, blue-white appearance. It is often associated with a CCT near 6500K, but the exact Kelvin value on the product is authoritative.
WW — Warm White
A warm, yellow-white appearance, commonly near 3000K. WW is a colour label, not a lumen or efficiency grade.
NW — Natural or Neutral White
A balanced white appearance, commonly near 4000K. Naming boundaries vary, so compare the numeric CCT.
CCT — Correlated Colour Temperature
The colour appearance of a nominally white light source, expressed in kelvin (K). Lower values appear warmer and higher values cooler. CCT does not state brightness.
CRI — Colour Rendering Index
A family of measures used to describe how a light source renders colours compared with a reference. A single general CRI value does not describe every test colour and should not be inferred from CCT.
Light quantities
Lumen (lm)
The SI unit of luminous flux: total visible light output. Compare lumens when the question is how much light a lamp or luminaire emits.
Lux (lx)
The SI unit of illuminance: one lumen per square metre at a surface. Lux changes with distance, distribution, angle and obstructions.
Watt (W)
The unit of power. For a light, watts describe electrical input at a rate; they do not directly describe brightness.
Lumens per watt (lm/W)
A ratio calculated as lumens divided by watts. It expresses luminous efficacy for the stated boundary—lamp or complete luminaire—which must be consistent when products are compared.
Luminous efficacy
The effectiveness with which electrical input is converted to visible light, commonly expressed in lm/W. It is different from efficiency in percent and does not by itself cover glare, colour quality or life.
Electrical performance
Power factor (PF)
The ratio of real power to apparent power in an AC circuit. It is dimensionless and product-specific. Do not infer PF from wattage.
THD — Total Harmonic Distortion
A measure describing harmonic content relative to the fundamental waveform. Current THD and voltage THD are not interchangeable; use the product/test declaration.
SPD — Surge Protective Device
A device intended to limit transient overvoltage and divert surge current under defined conditions. Its rating, coordination and installation are engineering matters; “surge protected” without a value is insufficient for specification.
LED driver
The electronic power-control component that supplies an LED light engine. Drivers may provide current regulation, dimming or protection. Compatibility must be verified.
Protection and construction
IP rating
An ingress-protection code for an enclosure. The first numeral relates to solid objects/dust and the second to water. A rating applies to the tested enclosure and installation condition.
IK rating
A code classifying resistance of an enclosure to external mechanical impact under defined test conditions. It is not a general durability guarantee.
COB — Chip on Board
An LED packaging approach in which multiple dies are mounted closely on a substrate. COB does not by itself specify beam angle, brightness or quality.
SMD — Surface-Mount Device
An electronic component mounted directly on a circuit-board surface. In lighting it often refers to packaged LEDs used in arrays; the finished luminaire determines performance.
Beam angle
A convention describing angular spread around the beam axis, usually referenced to a specified intensity threshold. It does not describe all spill light or guarantee spacing.
How specifications interact
| Buying question | Primary evidence | Secondary checks |
|---|---|---|
| How much total light? | Lumens | Distribution, mounting and shade losses |
| How much power? | Watts | Operating hours and quantity |
| How efficiently? | lm/W using compatible boundaries | Optical usefulness and other quality metrics |
| What colour appearance? | CCT in kelvin | CRI, colour tolerance and finishes |
| How much reaches the task? | Lux or a photometric calculation | Uniformity and glare |
| Will it suit outdoors? | Model-specific IP/IK and installation instructions | Surge design, drainage, seals and maintenance |
Avoid acronym-led purchasing
A long specification is not automatically a good one. Each value should connect to the installation. An indoor bulb may not need an outdoor IP rating; a road luminaire may need far more optical, electrical and environmental evidence than a household lamp. Define the job, then request the terms that decide it.
Do not copy a value from a family brochure onto every model. Wattage, CCT, driver option and optic can change performance. For a comparison, keep the model code and source document beside every number.
Read units carefully
lm and lx are not interchangeable, W is not Wh or kWh, and lm/W is not a percentage. IP and IK codes use different test concepts. PF is a ratio, while THD should identify whether current or voltage distortion is meant. A misplaced unit can turn a plausible specification into a meaningless one.
How to use these terms together
For a purchase, lumens answer output, watts answer input, lm/W answers efficacy, CCT answers colour appearance, and optical data helps explain where light goes. PF, THD, ingress, impact and surge data answer different engineering questions. No single metric is a quality score.