Why measure before you specify
A lighting retrofit specified from a floor plan and a lux calculation is a guess. The actual performance of the existing installation — how much light is reaching work surfaces, what the colour rendering quality is, whether there's significant flicker, and whether the spectral content is appropriate for the tasks being performed — is only knowable from measurement. Spektris uses calibrated UPRTek spectral meters to provide objective data at every measurement point, producing a baseline that makes the retrofit specification defensible and the post-installation comparison meaningful.
What spectral measurement covers
Illuminance (lux)
Measured at the working plane against CIBSE SLL Code for Lighting zone requirements: 300–500 lux for general office work, 750 lux for drawing offices, 200 lux for corridors. Average, minimum, and maximum values per zone with uniformity ratio (Emin/Eavg). Comparison against BS EN 12464-1 maintained illuminance targets.
Colour metrics
Colour temperature (CCT in Kelvin) — warm white (2700–3000K), neutral (3500–4000K), cool white (5000–6500K). Colour rendering index (CRI/Ra) — the measure of how accurately the light source renders colours compared to natural light. Ra 90+ is required for colour-critical tasks; Ra 80+ is the minimum acceptable for most commercial interiors. R9 value specifically — the rendering of deep red, which drops sharply in lower-quality LEDs and affects skin tones, food presentation, and product assessment.
Biological and health metrics
Melanopic EDI (Equivalent Daylight Illuminance) — the measure most relevant to circadian rhythm support. WELL Building Standard v2 requires melanopic EDI ≥ 250 lux at the eye level by 9am for spaces intended to support alertness. EML (Equivalent Melanopic Lux) is the older metric still used in many WELL assessments. Both are calculated from the full spectral power distribution captured by the UPRTek meter — not estimated from manufacturer CCT data.
Flicker
Flicker percentage and flicker index, measured at 100Hz and 120Hz (the dominant frequencies from LED drivers on 50Hz and 60Hz mains supplies). IEEE 1789-2015 risk categories: low risk below 1% flicker at 100Hz. Stroboscopic effect visibility index (SVM) where relevant for spaces with moving equipment.
Glare
Unified Glare Rating (UGR) — calculated from luminaire photometric data and room geometry against the measurement data. UGR < 19 is the standard for VDU-intensive office work. Uniformity mapping — identifying areas of excessive contrast between task area and immediate surround that cause visual discomfort.
Instrumentation: UPRTek calibrated spectral meters are the professional standard for light quality measurement in the UK and EU, used by lighting designers, WELL assessors, and FM teams. Calibration certificates are provided with every survey report.
Survey output
Every survey produces a zone-by-zone measurement report in PDF and Excel formats including: measurement point map (annotated floor plan), full data table per point, CIBSE compliance summary, WELL criteria checklist, pre/post retrofit comparison template (completed post-retrofit), and a written interpretation of the results with retrofit recommendations where applicable.