luminous intensity
C2Technical/Scientific
Definition
Meaning
A photometric measure of the power of a light source to produce visible light in a given direction, per unit solid angle.
In physics and engineering, it is the fundamental quantity defining the brightness of a light source as perceived by the human eye, weighted by the spectral sensitivity of the eye. It is the basis for defining the candela, the SI base unit.
Linguistics
Semantic Notes
This is a precise scientific term, not a general synonym for 'brightness'. It is a directional property, distinct from luminous flux (total light output) and illuminance (light falling on a surface).
Dialectal Variation
British vs American Usage
Differences
No significant lexical or spelling differences. The term is identical in both varieties. Potential minor differences in pronunciation of 'luminous'.
Connotations
Purely technical, no connotative differences.
Frequency
Equally rare outside technical contexts in both varieties.
Vocabulary
Collocations
Grammar
Valency Patterns
The luminous intensity of [light source] is [value] candelas.[Light source] has a luminous intensity of [value].to measure/calculate/determine the luminous intensity.Vocabulary
Synonyms
Neutral
Weak
Vocabulary
Antonyms
Usage
Context Usage
Business
Rare. Used in specifications for lighting products, LED manufacturing, and safety standards.
Academic
Core term in physics, photometry, optical engineering, and lighting design courses.
Everyday
Virtually never used. People say 'brightness' instead.
Technical
Primary context. Used in datasheets, scientific papers, optical design software, and photometry labs.
Examples
By Part of Speech
adjective
British English
- The luminous-intensity measurement was critical.
American English
- The luminous-intensity value is given in candelas.
Examples
By CEFR Level
- The car's headlight must have a minimum luminous intensity to be legal.
- LEDs often have a very high luminous intensity for their size.
- The engineer calibrated the device to measure the luminous intensity distribution of the new spotlight.
- According to the standard, the luminous intensity in the main beam must exceed 10,000 candelas.
Learning
Memory Aids
Mnemonic
Think of a lighthouse: LUMINOUS INTENSITY is how strong its beam is in one specific direction, not how much total light it spills everywhere.
Conceptual Metaphor
LIGHT AS A MEASURABLE FORCE (intensity implies strength/power).
Watch out
Common Pitfalls
Translation Traps (for Russian speakers)
- Do not confuse with 'яркость' (brightness/luminance) which often refers to luminance (light per unit area). 'Luminous intensity' is 'сила света', a directional quantity.
Common Mistakes
- Using 'luminous intensity' to describe how bright a surface appears (that's luminance).
- Confusing it with 'luminous flux' (total light output).
- Omitting the directional aspect.
Practice
Quiz
What does 'luminous intensity' specifically measure?
FAQ
Frequently Asked Questions
The candela (cd), which is one of the seven base SI units.
Not exactly. 'Brightness' is a subjective perception. Luminous intensity is an objective, quantifiable photometric measure. In technical contexts, 'brightness' often incorrectly substitutes for luminance or luminous intensity.
Luminous flux (measured in lumens) is the total visible light power emitted by a source in all directions. Luminous intensity (measured in candelas) is the flux emitted in a specific direction per unit solid angle.
Primarily in technical fields: lighting design, automotive lighting regulations, flashlight specifications, optical physics, and photometric testing reports.