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CircadianLab — EML, Illuminance & Glare Calculator

CircadianLab is a free lighting analysis tool that calculates three key metrics: melanopic equivalent lux (EML) for circadian lighting design, illuminance in lux and foot-candles for general lighting analysis, and UGR (Unified Glare Rating) for visual comfort assessment. All calculations use real IES photometric data with radiosity simulation for accurate indirect light modeling.

Use it to design lighting layouts that meet WELL v2 Feature L03 requirements, verify illuminance levels against IES/CIE standards, evaluate glare comfort per CIE 117:1995, compare fixture options, and generate professional reports — all in your browser with no signup required.

What is EML and Why Does It Matter?

Traditional lighting design focuses on photopic illuminance (lux) — how bright a space appears to the human visual system. But the non-visual effects of light on circadian rhythms depend on a different metric: melanopic equivalent daylight illuminance.

EML is calculated as: EML = Illuminance (lux) × Melanopic DER

The melanopic Daylight Equivalent Ratio (DER) depends on the spectral power distribution of the light source and varies with color temperature (CCT). At 6,000K (daylight), the DER is 1.0 by definition. Warm LEDs (2,700K) have a DER of ~0.44, meaning they produce less than half the melanopic stimulation per lux compared to daylight. High-CCT sources like Innerscene Circadian Sky at 40,000K achieve DER values of ~1.53.

WELL v2 Feature L03 — Circadian Lighting Design

The WELL Building Standard v2 requires spaces to provide adequate melanopic light at eye level for occupant health and wellbeing:

  • Tier 1: ≥150 melanopic EDI in at least one vertical direction at 1.2m (seated eye height)
  • Tier 2: ≥275 melanopic EDI in at least one vertical direction at 1.2m

This calculator checks compliance at every measurement grid point and reports the percentage that passes each tier. The vertical-direction requirement means ceiling-mounted downlights alone often fall short — wall-mounted fixtures at eye level can be far more effective for melanopic stimulation.

How the Simulation Works

Direct Illuminance

Each fixture's intensity toward every measurement point is computed using IES Type C photometry with inverse-square law attenuation and cosine incidence correction. Area sources use 12×12 subdivision integration.

Radiosity (Indirect Light)

A 3-bounce iterative radiosity solver computes form factors between all surface patches, then solves for inter-reflected light. This captures how walls, floors, and ceilings redirect light throughout the space.

Melanopic Conversion

Photopic illuminance is converted to EML using measured melanopic DER values. For Circadian Sky fixtures, a 22-point lookup table from real spectral measurements is used. Custom DER values can be provided for any fixture.

Directional Measurement

EML is computed in 5 directions at each grid point: horizontal (desk level) plus the 4 cardinal vertical directions (north, east, south, west) at eye height. WELL compliance requires only one vertical direction to pass.

Validated Calculations

Every calculation in this tool is verified by an automated validation suite — 120+ tests covering inverse-square law, cosine incidence, radiosity energy conservation, IES lumen integration, melanopic DER accuracy, and WELL v2 compliance logic. Tests run against 20 IES photometric files from 8 manufacturers including BEGA, Philips, American Electric Lighting, and Innerscene.

Features

IES Photometry

Load real measured photometric data from IES files for accurate light distribution modeling

Circadian Sky Presets

All 5 Innerscene Circadian Sky sizes with measured melanopic DER data

Wall Fixtures

Mount fixtures on any wall with height and tilt control for eye-level melanopic stimulation

WELL Compliance

Automatic Tier 1/2 checking at every grid point with pass/fail statistics

CCT Control

2,200K to 40,000K with real-time EML recalculation using variable melanopic DER

PDF Reports

Professional reports with heatmaps for all directions, fixture schedule, and QR code

Share Links

Save and share your exact session — room, fixtures, camera angle, and results

Custom IES Upload

Upload any IES file with custom melanopic DER for third-party fixtures

3D Visualization

Interactive 3D room view with orbit controls, heatmap texture, and occupant models

Ceiling Grid Snap

Rotatable ceiling grid with fixture snap alignment for precise troffer placement

Illuminance (Lux/FC)

Calculate horizontal and directional illuminance in lux or foot-candles with inverse-square law and IES photometry

UGR Glare Analysis

Unified Glare Rating per CIE 117:1995 with directional heatmaps, Guth position index, and per-occupant evaluation

Floor Illuminance

Separate floor-level analysis for emergency egress and ambient light distribution

Frequently Asked Questions

What is EML (melanopic equivalent lux)?
EML (Equivalent Melanopic Lux), formally known as melanopic EDI (Equivalent Daylight Illuminance), measures how effectively a light source stimulates the melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs) in the human eye. These cells regulate circadian rhythms, alertness, and sleep-wake cycles. EML is calculated by multiplying photopic illuminance by the melanopic Daylight Equivalent Ratio (DER), which depends on the spectral power distribution of the light source.
What is the WELL v2 requirement for melanopic light?
WELL v2 Feature L03 (Circadian Lighting Design) requires melanopic EDI of at least 150 lux (Tier 1) or 275 lux (Tier 2) measured vertically at eye level (1.2m for seated occupants) in at least one cardinal direction. At least 75% of workstations must meet this threshold for compliance.
What CCT produces the highest EML?
Higher color temperatures produce more melanopic light per lumen. At 40,000K, the melanopic DER reaches approximately 1.53 for Circadian Sky fixtures. Standard LEDs at 6,000K have a DER of 1.0 (the daylight reference), while warm 2,700K LEDs have a DER of only 0.44. This means a 40,000K fixture produces roughly 3.5× more EML per lux than a 2,700K fixture.
How does the Circadian Sky melanopic DER compare to standard LEDs?
Standard phosphor-converted white LEDs are commercially available up to about 6,500K, where they achieve a melanopic DER of approximately 1.10. Above that, standard LEDs become harsh, bluish, and lose color rendering quality — so most offices use 3,500–4,000K (DER 0.61–0.69) or at best 5,000K (DER 0.87). Fluorescent lamps perform even worse: a T8 at 4,000K achieves only DER 0.56. Innerscene Circadian Sky uses a 4-chip ATMOS platform with a tunable CCT range of 2,200K to 40,000K while maintaining CRI 91+ throughout. This means it can operate at CCTs far beyond what standard LEDs offer — for example, at 10,000K (DER 1.23), 15,000K (DER 1.37), or 40,000K (DER 1.53) — delivering 2–3.5× more melanopic stimulation per lux than a typical office LED, without any additional glare penalty since UGR depends on luminance, not spectral content. At the same CCT, Circadian Sky also slightly outperforms standard LEDs: 0.76 vs 0.69 at 4,000K and 0.89 vs 0.87 at 5,000K.
What is radiosity in lighting simulation?
Radiosity is a global illumination method that simulates how light bounces between surfaces in a room. Unlike direct illuminance calculation alone, radiosity accounts for inter-reflections — light that hits a wall, reflects off it, then illuminates other surfaces. This tool uses a 3-bounce iterative Gauss-Seidel radiosity solver with form factor computation, providing physically-based indirect lighting estimates.
What are IES files and why do they matter?
IES (Illuminating Engineering Society) files contain measured photometric data describing exactly how a luminaire distributes light in three dimensions. Using real IES data instead of simplified cosine distributions produces much more accurate illuminance predictions, especially for directional fixtures like troffers and wall washers. This tool supports IES Type C photometry with bilinear interpolation.
What fixtures are included in the built-in library?
CircadianLab includes a searchable library of over 8,600 photometric files from 40+ manufacturers including Innerscene, Acuity Brands (Lithonia, Juno, Aculux, Peerless, Gotham, Holophane), Cooper Lighting (Eaton), TCP Lighting, Luminii, BEGA, Thorn Lighting, LSI Industries, Artemide, Lightnet, GE Current, Planlicht, LIGMAN, ERCO, Lutron, Cree, ARRI, ETC, Signify (Philips), and more. Fixture types include downlights, area/flood lights, linear/strip, troffers, wall wash, spot/track, high bay, bollards, flat panels, film/studio lights, and theatre fixtures. You can also upload any IES file from any manufacturer not in the library.
How do wall-mounted fixtures affect EML?
Wall-mounted fixtures at eye level can dramatically increase vertical melanopic illuminance because they direct light horizontally toward the occupant's eyes. Ceiling-mounted downlights primarily illuminate horizontal surfaces, producing high desk-level lux but lower vertical EML. For WELL v2 compliance, wall-mounted fixtures at seated eye height (1.2m) are often more effective per lumen than ceiling fixtures.
How does the illuminance calculator work?
CircadianLab calculates photopic illuminance in both lux and foot-candles using IES photometric data and inverse-square law physics. It computes illuminance on horizontal surfaces (desk level) and in all four cardinal vertical directions at eye height. The radiosity engine adds inter-reflected (indirect) light from walls, floor, and ceiling for realistic total illuminance predictions. Switch between lux and foot-candles using the metric/imperial toggle.
What is UGR (Unified Glare Rating)?
UGR (Unified Glare Rating) per CIE 117:1995 is the international standard metric for assessing discomfort glare from luminaires. The formula accounts for luminaire luminance, solid angle, background luminance, and the Guth position index based on the source's elevation and horizontal angle relative to the observer's line of sight. UGR ≤16 is very comfortable, ≤19 is suitable for offices, ≤22 is acceptable for industrial settings, and ≤25 is the limit for corridors. This tool calculates UGR heatmaps across the entire room and per-occupant values based on viewing direction.
What is the difference between lux and foot-candles?
Lux and foot-candles both measure illuminance (luminous flux per unit area) but use different units. 1 foot-candle = 10.764 lux. Foot-candles are commonly used in North American lighting design (IES standards), while lux is the SI unit used internationally (CIE standards). Typical office lighting targets are 30–50 fc (300–500 lux) on the work plane. CircadianLab supports both units and automatically converts between them.
Can I share my lighting design with someone?
Yes. Click the Share button to save your current session (room, fixtures, camera angle, selections) to a unique URL. Anyone with the link sees exactly what you see, including the heatmap results. Each share generates a new UUID — the simulation state is stored server-side and can be reopened at any time.
Is this tool free to use?
Yes, CircadianLab is completely free with no signup required. All calculations run in your browser using a Web Worker. You can upload custom IES files, generate PDF reports, and share links without any account or payment.

Supported Fixtures & IES Photometric Library

CircadianLab includes a built-in library of 0 photometric files from 0 manufacturers, covering 0 fixture categories: . You can also upload any IES file from any manufacturer.

Related Tools & Resources

Validation Suite
120+ tests against 20 IES files from 8 manufacturers
DWG Viewer
View AutoCAD DWG files online
SKP Viewer
View SketchUp 3D models online
Circadian Sky
Innerscene circadian lighting fixtures
Virtual Sun
Artificial skylight technology
WELL Standards
WELL Building Standard resources
Research
Circadian lighting research library

This tool is for design guidance only. Actual field conditions may differ due to furniture, finishes, maintenance factors, and other variables not modeled. Melanopic calculations follow CIE S 026:2018. WELL compliance assessment is based on WELL v2 Feature L03 requirements.