Who this tool is for
The SPD Analyzer turns any spectroradiometer file into the metrics specifiers actually need to put on drawings, datasheets, and submittals — without installing software, paying a subscription, or uploading anything to a server.
Lighting designers & electrical engineers
Drop the SPD CSV from your spectroradiometer (JETI specbos, Sekonic C-7000, Konica Minolta CL-500A, GL Spectis) and instantly get CCT, Duv, CRI Ra, R9, R12, and α-opic ratios in the format you need for fixture submittals and lighting plans.
WELL APs & sustainability consultants
Compute melanopic-EDI, mel-DER, and α-opic ratios per CIE S 026:2018 — the exact metric WELL v2 Feature L03 references. Side-by-side WELL threshold checks (150 / 200 / 275 lx mel-EDI) for Part 1, Tier 1, and Tier 2.
Architects on healthcare, hospitality & wellness projects
Validate that fixtures specified for circadian benefit (ICU, oncology, long-term care, hospitality, residential wellness) actually deliver the spectral content their datasheets claim. Compare CCTs side-by-side with a tunable-CCT slider.
Lighting researchers & LED engineers
Quickly check S/P, M/P, α-opic ELR, chromaticity (x, y, u′, v′), spectral band contributions, and Planckian locus position for any new lamp, phosphor mix, or multichip combination. Use the bundled Node CLI for batch analysis.
About this tool
The SPD Analyzer computes the metrics that matter for circadian-aware lighting specification: melanopic Daylight Equivalent Ratio (DER) per CIE S 026:2018, correlated color temperature (CCT) via the Ohno 2014 method, Duv, CIE 13.3-1995 CRI (Ra and R1–R14), and the α-opic responses for all five photoreceptor classes.
All calculations are performed locally in your browser using validated CIE reference data — your file never leaves your device.
For room-level mel-EDI calculations across an actual fixture layout, use CircadianLab with our 250,000+ IES file library. To inspect a goniophotometric IES file, use the IES Viewer.
What do these numbers mean?
Lighting metrics use a lot of acronyms. Here's a plain-language guide to what each one tells you, why it matters for the people sitting under the light, and where to read more.
mel-EDI / mel-DER
How much of the light is "circadian-active" — the part your body's non-visual photoreceptors (ipRGCs / melanopsin) actually respond to. Higher mel-EDI during the day = better alertness, mood, and night-time sleep quality. Lower in the evening = easier to fall asleep.
mel-EDI is in lux: "how many lux of D65 daylight would produce the same circadian effect as your light." mel-DER is the dimensionless ratio (D65 = 1.000).
CCT (Correlated Color Temperature)
The "warm vs cool" appearance of the light, measured in kelvin. 2700 K is the warm orange of an old incandescent; 4000 K is neutral office white; 6500 K is overcast daylight; above 10 000 K is the deep blue of a clear northern sky. Specified by virtually every product datasheet and lighting plan.
Duv
How "off-white" the light is — distance from the pure blackbody curve. Positive Duv = greenish tint above the locus; negative = pinkish/magenta below. ANSI specifies "white" as |Duv| < 0.006. Most sources at |Duv| > 0.01 look visibly tinted.
CRI (Color Rendering Index)
How accurately the light renders colors compared to a reference (Planckian or daylight) at the same CCT. Ra is the average of R1–R8 (eight pastels); R9 is saturated red; R12 is deep blue. Above 90 = excellent; 80 = typical LED office; below 70 = noticeably distorted (skin looks gray, food looks muted). Hospitality and clinical settings target Ra ≥ 90 with R9 ≥ 80.
α-opic responses (S, M, L cone, rhodopic, melanopic)
The five photoreceptor classes in the human retina. Three cones drive color vision (S = blue, M = green, L = red), rods (rhodopic) handle low-light vision, and melanopsin (melanopic) drives circadian rhythm, pupil response, and alertness. Each one has its own spectral sensitivity curve, and CIE S 026 lets us quantify how strongly any light source stimulates each one.
WELL v2 L03 thresholds
The WELL Building Standard's circadian lighting feature defines minimum mel-EDI at occupant eye height (1.2 m, vertical plane) for at least 4 daytime hours. 150 lx meets L03 Part 1; 200 lx earns Tier 1; 275 lx earns Tier 2. The dashed gold lines on the output chart mark these levels.
Standards and calculation details
Color metrics
- CIE 1931 2° standard observer (ISO/CIE 11664-1:2019) — color-matching functions x̄, ȳ, z̄ integrated at 5 nm.
- CCT — Ohno 2014 modified parabolic search on the Planckian locus, range 1 000 K to 100 000 K. Beyond ~100 000 K the locus has asymptoted; sources whose chromaticity falls outside that range will report Duv larger than the CIE 15:2004 validity threshold of ±0.05. Background: Circadian Sky CCT range, measuring color, color consistency / MacAdam ellipses.
- Duv — signed distance from the Planckian locus in CIE 1960 UCS; positive = above locus (greenish), negative = below (magenta-ish). See: Duv in lighting.
- CRI Ra and R1–R14 — per CIE 13.3-1995. Reference illuminant: Planckian (CCT < 5 000 K) or CIE D-illuminant (≥ 5 000 K). Chromatic adaptation: CIE 1964 von-Kries-like; color difference in W*U*V* (CIE 1964 UCS); Rᵢ = 100 − 4.6 ΔE. Background: CRI, R9, and TM-30.
α-opic and circadian metrics
- Action spectra — CIE S 026:2018 (S/M/L cone, rhodopic, melanopic), peak-normalized to 1.0. Source: official CIE ToolBox v1.049 SI Action Spectra dataset.
- α-opic DER (Daylight Equivalent Ratio) per CIE S 026:2018 Annex B — self-normalized against D65, so absolute SPD scaling is not required. By construction DERα = 1.000 for D65 in all five photoreceptor classes.
- α-opic ELR (Equivalent Luminous Radiation, mW/lm) per the CIE S 026 toolbox conventions.
- mel-EDI = photopic illuminance × mel-DER. By definition, D65 produces 1 mel-EDI lx per photopic lx.
- WELL v2 L03 thresholds — 150 lx mel-EDI (Part 1), 200 lx (Part 2 Tier 1), 275 lx (Part 2 Tier 2), measured vertically at eye height (1.2 m). See WELL v2 — Feature L03 official spec and Innerscene's WELL standards summary.
Ingest, sampling, and integration
- Inputs accepted: IES TM-27-20 SPDX (XML) and tolerant CSV/TSV — auto-detect of comma / tab / semicolon delimiters, dot or comma decimal separators, header-heavy files, multi-column files with a column picker.
- All inputs are resampled to a 5 nm grid (380–780 nm) via linear interpolation. Colorimetric and α-opic integrals use Riemann sums with Δλ = 5 nm, which matches the CIE-recommended sampling for these calculations.
- Source wavelengths outside 380–780 nm are zero-padded. Narrow-band warnings appear when the source starts after 460 nm (biases melanopic) or ends before 700 nm (biases red CRI).
Reference data and validation
- CIE 1931 2° CMFs, D65 illuminant, CIE 13.3-1995 TCS reflectances, and CIE 15:2004 D-series basis functions are sourced from colour-science. CIE S 026:2018 α-opic action spectra come from the official CIE ToolBox v1.049 dataset shipped with luxpy. The full pipeline is validated against 28 CIE / IES reference illuminants (A, D50/D55/D60/D65/D75, C, E, FL1–FL12, FL3.1/.5/.10/.15, HP1–HP4) — all CCT, Duv, x/y, and CRI Ra values match colour-science's ground truth within published tolerances.
Related Innerscene resources
- CircadianLab — full room radiosity simulation with 250 000+ IES files, computes mel-EDI at occupant eye height with WELL L03 compliance checks.
- IES Viewer — inspect goniophotometric IES files: 2D/3D polar plots, beam analysis, iso-footcandle plots.
- Health impacts of artificial light — overview of circadian, sleep, and mood effects.
- Circadian Sky — Innerscene's tunable-CCT artificial skylight measured by the SPD file used in this tool's sample.
- Circadian Sky spec help — full library of articles on CCT, CRI, Duv, melanopic, multichip technology, and more.
A note on the Innerscene Circadian Sky published values
The bundled Circadian Sky photometric report (the multi-CCT JETI export shipped with the product) was generated against the predecessor standard CIE TN 003:2015, not the current CIE S 026:2018. Its "Melanopic Ratio" column runs uniformly ~10% higher than the values shown here — a flat 0.906× offset that holds across every CCT from 2 200 K to 200 000 K. Both numbers are correct against their respective references; this tool reports the current CIE S 026:2018 values that WELL v2 L03 and 2019+ photobiology literature use. CCT, Duv, and CRI columns from the same xlsx match this tool's output within rounding precision (Ra delta < 0.1, CCT delta < 50 K).
Frequently asked questions
What is melanopic EDI and how do I calculate it?
Melanopic Equivalent Daylight Illuminance (mel-EDI), measured in lux, is the integral of the source spectrum weighted by the CIE S 026:2018 melanopic action spectrum, calibrated so D65 daylight produces 1 mel-EDI lux per photopic lux. This tool computes it from any SPD: mel-EDI = photopic illuminance × mel-DER. WELL v2 L03 requires mel-EDI ≥ 150 lx for Part 1, ≥ 200 lx for Tier 1, ≥ 275 lx for Tier 2.
What's the difference between mel-DER, mel-EDI, and Melanopic Ratio?
mel-DER (Daylight Equivalent Ratio) is dimensionless, equal to 1.000 for D65 by definition. mel-EDI (Equivalent Daylight Illuminance) is mel-DER multiplied by photopic illuminance, in lux. The older term "Melanopic Ratio" is essentially mel-DER but typically refers to the pre-CIE-S-026:2018 normalization, which runs ~10% higher than current values.
How do I calculate CCT from an SPD?
Correlated Color Temperature is computed from the SPD by integrating against the CIE 1931 standard observer to get tristimulus XYZ, converting to CIE 1960 UCS (u, v), then finding the closest point on the Planckian locus. This tool uses the Ohno 2014 method (golden-section refined search) over 1000–100 000 K. The result reads as a single Kelvin value.
Does this tool work for WELL v2 L03 compliance?
Yes. The tool reports mel-EDI per CIE S 026:2018 (the standard WELL v2 references) and visualizes the 150 / 200 / 275 lx thresholds for L03 Part 1, Tier 1, and Tier 2. For room-level mel-EDI at occupant eye height with multiple fixtures, see the CircadianLab tool which adds radiosity simulation on top of the SPD math.
What spectroradiometer file formats are supported?
IES TM-27-20 SPDX (XML) and a wide range of CSV/TSV exports — including JETI specbos, Sekonic C-7000, Konica Minolta CL-500A, and GL Spectis formats. The parser auto-detects delimiter (comma/tab/semicolon), decimal separator (dot or comma), and metadata-row header structure. Multi-column files (e.g. tunable-CCT fixtures with one SPD per CCT) are supported with a CCT slider.
How accurate is the CRI calculation?
The CRI Ra and R1–R14 implementation follows CIE 13.3-1995 exactly: Planckian reference for CCT < 5000 K, CIE D-illuminant for ≥ 5000 K, CIE 1964 von-Kries chromatic adaptation, W*U*V* color difference. Validated against published values for 28 CIE/IES illuminants (D-series, F-series, A, FL3.x, HP1–HP4) within rounding precision (<0.1 Ra delta).
Do I need to install software or upload my files?
Neither. The entire computation runs locally in your browser — your SPD file never leaves your device. Drag-and-drop a CSV or TM-27 SPDX onto the page or use the built-in samples (D65, blackbodies at common CCTs, Innerscene Circadian Sky multi-CCT data).