Quick Answer
Lux meter calibration uses a NABL-calibrated reference illuminance meter and a stable standard light source (A-type tungsten halogen lamp at known colour temperature) to verify the lux meter's reading accuracy at defined illuminance levels (typically 100 lux, 500 lux, 1000 lux, 5000 lux).
Key Takeaways
- Lux meter calibration uses a reference standard lamp at known colour temperature (2856 K Type A).
- Calibration points: 100, 500, 1000, 5000, 10000 lux (depending on meter range).
- Spectral mismatch correction factor (f₁) is important for LED and fluorescent lamp accuracy.
- Cleanroom light level verification (ISO 14644-3) requires calibrated lux meters.
- Prism calibrates lux meters, UV intensity meters, and UV dosimeters.
Applications Requiring Calibrated Lux Meters
- Workplace lighting compliance (Factory Act, IS 3646 — 500 lux for fine work)
- Pharmaceutical cleanroom lighting verification (ISO 14644-3)
- Operating theatre and hospital lighting (300–1000 lux per IS 12460)
- Forensic and inspection lighting for quality control
- UV curing system intensity monitoring (UV-A, UV-B, UV-C meters)
- Solar irradiance measurement (pyranometer calibration for solar farms)
- Emergency lighting testing and maintenance (IS 12193)
Lux Meter Calibration Procedure
Standard Source Setup
Set up calibrated tungsten halogen standard lamp at known power setting. Allow 30-minute stabilisation.
Reference Placement
Place NABL-calibrated reference photometer at defined distance from source. Record reference illuminance.
Test Meter Measurement
Place lux meter at same distance. Record lux meter reading and calculate error vs. reference.
Multi-Level Test
Repeat at 3–5 illuminance levels by adjusting lamp distance or power. Cover the meter's full range.
Certificate
Issue NABL certificate with calibration factor, error at each point, and expanded uncertainty (typically ±3–5%).
Frequently Asked Questions
Why does lux meter accuracy depend on the light source type?
Lux meters use silicon photodiodes with spectral response different from the human eye's V(λ) curve. The spectral mismatch correction (f₁ factor) means a lux meter calibrated with incandescent light will give different readings under LED or fluorescent light. For highest accuracy, calibrate the lux meter with the same type of light source used in the measurement environment.
How often should lux meters be calibrated?
Annual NABL calibration is standard. Lux meters used for Factory Act inspection or cleanroom qualification should be calibrated annually.
Does Prism calibrate UV intensity meters?
Yes. Prism calibrates UV-A (315–400 nm), UV-B (280–315 nm), and UV-C (200–280 nm) intensity meters using calibrated UV reference radiometers and NABL-certified UV light sources.
Can Prism calibrate pyranometers for solar farm monitoring?
Yes. Prism calibrates pyranometers (solar irradiance sensors) used for solar PV farm performance monitoring and yield analysis, in the 300–2500 nm solar spectrum range.
What is the NABL uncertainty for lux meter calibration at Prism?
Prism achieves expanded uncertainty of ±3–5% (k=2) for lux meter calibration using Type A tungsten standard lamp. LED source calibration may have higher uncertainty (±5–8%) due to spectral mismatch.
Written by
Er. Parthiv Kinariwala
Managing Director · Prism Calibration Centre · NABL CC-2480 · Ahmedabad
Er. Parthiv Kinariwala founded Prism Calibration Centre in 2004 and has over 20 years of hands-on experience in calibration engineering, NABL accreditation, and industrial compliance. His team performs 10,000+ calibrations annually from the Vatva GIDC laboratory, serving 5000+ industries across Gujarat.
Prism Calibration Centre — Vatva GIDC, Ahmedabad
Prism Calibration Centre
F-101, Rudraksh Complex 2, Phase 3, GIDC Vatva, Near Jasoda Nagar Cross Road, Ahmedabad — 382445, Gujarat, India
Phone: +91 98245 26444
Email: info@prismcalibration.com
NABL: CC-2480 · ISO/IEC 17025:2017
Hours: Mon–Sat, 9:00 AM – 7:00 PM