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.

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.

Higher color temperatures produce more melanopic light per lumen. At 200,000K, the melanopic DER reaches approximately 1.89 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 200,000K fixture produces roughly 3.5× more EML per lux than a 2,700K fixture.

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 200,000K 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 200,000K (DER 1.89) — 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.

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.

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.

CircadianLab includes a searchable library of over 250,000 photometric files from 70+ 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.

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.

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.

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.

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.

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.

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.

Yes. CircadianLab simulates daylight through wall windows and skylights using the NREL Solar Position Algorithm for sun position (any date, time, and geographic location) and a Perez sky model for diffuse and direct horizontal/normal illuminance. Direct sun and diffuse sky contributions are added as initial flux on every radiosity patch and measurement point, then bounced through the same form-factor network as electric fixtures — so daylight and electric light are solved together in one unified radiosity pass. Glazing transmittance, reflectance, and diffusion are configurable per window. The result: a single combined heatmap showing total photopic illuminance and melanopic EML from all sources.

That is correct physics. Atmospheric airmass — the column of air sunlight passes through — is roughly 1/sin(altitude). At sun altitude 25° the airmass is ~2.4 and clear-sky DNI is around 64,000 lux; at altitude 2.5° (15 minutes before sunset on the winter solstice in Chicago) the airmass jumps to ~18 and DNI collapses to ~770 lux. Combined with the small cos(zenith) factor on horizontal surfaces, the workplane sees only a few foot-candles of direct beam. Move the time slider toward solar noon to see thousands of foot-candles in the same beam.