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Which lamp has the best Colour Rendering Index (CRI)?
LED
Fluorescent
Incandescent
High pressure sodium vapour
Incandescent
The Colour Rendering Index (CRI) is a measure of a light source's ability to reveal the true colors of objects compared to an ideal or natural light source. Incandescent lamps produce light through black-body radiation, providing a continuous spectrum that encompasses all visible wavelengths, resulting in an ideal CRI of 100.
The Colour Rendering Index (CRI) is a measure of a light source's ability to reveal the true colors of objects compared to an ideal or natural light source. Incandescent lamps produce light through black-body radiation, providing a continuous spectrum that encompasses all visible wavelengths, resulting in an ideal CRI of 100.
CRI=RaтАЛ=81тАЛтИСi=18тАЛRiтАЛ тАФ Calculation of General Color Rendering Index
Incandescent lamps function by heating a tungsten filament to incandescence using electrical current. This thermal emission follows Planck's Law of black-body radiation, which inherently includes a balanced distribution of spectral colors across the entire visible range. Because the spectral power distribution matches that of a thermal radiator, it yields perfect color fidelity.
CRI ranges from 0 to 100.
Sunlight and black-body radiators like incandescent bulbs define the reference index of 100.
Discharge lamps often exhibit 'spectral gaps' which lower their CRI compared to incandescent sources.
High CRI is essential in applications like color printing, surgery, and retail.
Excellent color accuracy (CRI ~ 100)
Simple construction and low cost
No external ballast or control gear required
Extremely low luminous efficacy
Short operational lifespan
High heat emission leading to energy waste
Home accent lighting
Photography and film set lighting
Calibration equipment
LED technology has significantly improved and many modern high-end LEDs now achieve CRI values > 95, but incandescent remains the theoretical benchmark for 'perfect' color.
Sodium vapour lamps have very poor CRI, often making it difficult to distinguish colors (appearing mostly monochromatic yellow).
C is correct тАФ Incandescent lamps operate on the principle of thermal radiation, providing a continuous spectral power distribution that results in a perfect CRI of 100.
In illumination exams, always associate 'Continuous Spectrum' with high CRI and 'Discharge/Line Spectrum' with lower CRI.