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What is melanopic lux?

By Spektrum Glasses Editorial Team · Published 2026-08-07 · Updated 2026-08-07 · Facts re-checked 2026-08-07 How this page is written and checked: our editorial method · how we verify claims

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Short answer

Melanopic lux is a measure of light weighted by the sensitivity of the melanopsin system in the eye, which peaks near 480 nm rather than the 555 nm peak of ordinary photopic lux. Two lamps that look equally bright can deliver very different melanopic lux, because the weighting follows spectrum rather than perceived brightness.

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What melanopic lux actually measures

Ordinary lux is a photometric unit: it takes the raw radiant power arriving at a surface and weights it by the photopic luminous efficiency function, the curve describing how sensitive human daytime vision is at each wavelength. That curve peaks near 555 nm, in the green, and falls steeply toward both the blue and red ends of the spectrum. Lux is therefore a brightness metric, tuned to cones. Melanopic lux uses the same arithmetic with a different weighting curve. Instead of cone sensitivity, it weights each wavelength by the sensitivity of melanopsin, the photopigment found in a small population of intrinsically photosensitive retinal ganglion cells (ipRGCs). Melanopsin’s action spectrum peaks around 480 nm, in the blue-cyan, with meaningful sensitivity roughly from 420 nm to 540 nm and very little response above about 570 nm. These cells signal ambient light level to the parts of the brain that track time of day, which is why melanopic quantities are the standard input variable in circadian lighting research. You will also see the term melanopic equivalent daylight illuminant lux, or melanopic EDI. That form normalizes to daylight: a source with the same melanopic effect as a given photopic level of standard daylight is assigned that value, so daylight has a melanopic-to-photopic ratio of 1.0 by definition and other sources are expressed relative to it.

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Why photopic lux and melanopic lux disagree

Because the two curves peak roughly 75 nm apart, the ratio between them depends entirely on the shape of the source spectrum. A warm, red-heavy source such as a low-color-temperature filament lamp puts most of its output where melanopsin barely responds, so its melanopic lux is a fraction of its photopic lux. A cool, daylight-type white LED puts a strong peak near 450-460 nm right under the melanopic curve, so its melanopic lux approaches or matches its photopic lux. The practical consequence is that brightness is not a usable proxy. Two rooms metered at the same lux with a standard light meter can differ by several times in melanopic lux. Conversely, a room that looks dim can be melanopically significant if the source is blue-rich. Any figure you find quoted for a specific lamp comes from that lamp’s measured spectral power distribution; there is no way to derive it from wattage, color temperature alone, or the number printed on a light meter. One detail is routinely lost in consumer writing: melanopic lux is defined at the eye. The convention is vertical illuminance at the corneal plane, facing the direction of gaze. A ceiling fixture measured on a desk surface and the same fixture measured at eye level looking forward give different answers. A phone held 30 cm from the face and a television 3 m away can produce similar melanopic exposure despite hugely different screen sizes, because illuminance falls off with distance squared.

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How a lens changes the number

A filter’s effect on melanopic lux is computable but not guessable. You take the source spectrum, multiply it wavelength by wavelength by the lens transmittance curve, then re-weight the result with the melanopic curve and compare to the unfiltered case. What matters is transmittance specifically in the 440-520 nm region, where the melanopic weighting carries most of its mass. Attenuation at 400 or 410 nm contributes almost nothing to a melanopic figure, because melanopsin has little sensitivity there and most light sources emit little there either. This is why an unqualified “blocks 99% of blue light” tells you nothing about melanopic lux. A lens can be entirely honest about 99.99% at 400 nm and still pass most of the light that the melanopic curve cares about. Wavelength band is not a footnote to the percentage; it is the percentage. Here are our own measured figures, with the band each was measured over. Clear lens values are from COLTS Laboratories report O-SPG111015, an A2LA-accredited ISO/IEC 17025 laboratory, spectral transmittance per ANSI Z80.3.

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What our lenses do in the melanopic region, and where our data runs out

The clear lens is near-clear by design: it transmits 91.6% of visible light, so at most 8.4% of all visible photons are removed. Melanopic lux is a weighted subset of that same visible band, which puts a hard ceiling on how much melanopic reduction a lens like this can deliver. The measured curve supports that reading directly. Filtering drops from 99.99% at 400 nm to 63.0% at 420 nm to 33.1% at 450 nm, and we have not published a value at 480 nm, where the melanopic curve peaks. Given the slope, the attenuation there is lower still. A clear lens is the wrong instrument for lowering melanopic lux, and we would rather say that than imply otherwise. The ZENOX clear lens, averaging about 52% across the blue band, illustrates the same ceiling from the other direction: a lens that stays visually clear cannot take out the whole band. The tinted lenses are a different case. The amber evening lens removes 98.3% across 460-480 nm, which is the heart of the melanopic peak, and 97.9% across 400-500 nm. Orange removes 99.96% and red 99.83% across 380-500 nm. Those are large reductions in exactly the region that dominates a melanopic calculation. Even so, we cannot hand you a single melanopic-lux reduction percentage from these reports, and we will not fabricate one. Melanopic sensitivity has a real tail from 500 nm to about 540 nm, and our published measurements stop at 500 nm. A complete melanopic figure also depends on the source spectrum being filtered, so it is not a property of the lens alone. Separately: the orange and red lenses are not suitable for driving, at any time of day.

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What melanopic lux does not tell you

Melanopic lux is a dose metric for light. It describes the stimulus, not any response in a given person. It says nothing about comfort, and it is not interchangeable with the other blue-weighted quantity people encounter, the blue-light hazard function, which is a photochemical weighting curve centered at shorter wavelengths near 435-440 nm. A lens can score very differently on the two. Leung, Li and Kee, writing in PLOS ONE in 2017, found that commercially available blue-light-filtering lenses reduced the calculated blue-light hazard by roughly 10-24% — a useful reference point for how modest a near-clear filter’s effect on any weighted blue metric tends to be, and a hazard figure rather than a melanopic one. We make no claim about what any of our lenses do to a person. Our lab report measures transmittance, and that is all it measures. The evidence connecting consumer lens filtering to symptom outcomes is limited and contested, and this page is not the place to paper over that. If the goal is a lower melanopic dose in the evening, the largest levers are not optical at all. Melanopic lux scales linearly with source intensity, so dimming a lamp by 90% cuts it by 90% regardless of spectrum. It falls off with the square of distance, so moving a bright source further from the eye is unusually effective. Choosing warm, low-blue sources changes the ratio at the source. A heavily tinted lens is a real filter with real measured numbers, but it sits alongside those measures rather than replacing them, and it only helps to the extent that its attenuation band overlaps the melanopic curve.

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Where these numbers come from

Every measured figure quoted here is transcribed from a third-party laboratory report, published in full with the wavelength band and the report number: lab results. Our rule for what may appear on this page at all is on how we choose what to publish.

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