A $35 to $45 lux meter is enough to check that your SAD lamp really gives 10,000 lux at your face and to see if your desk gets anywhere near daylight. Reading melanopic light, the kind that sets the body clock, takes a spectrometer.
Daylight does most of the work for free. Start with sunlight first.
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A meter measures light; it does not treat anything, so this grade covers the light targets it checks. In a lab study of 55 young adults, evening light of about 25 lux halved melatonin on average, with a more than 50-fold spread in sensitivity between people, and campers living on natural light got over 4 times more daytime light (4,487 vs 979 lux) than at home. When 24 commercial light therapy devices were measured, only 7 met all three clinical criteria. No trial has tested whether owning a meter improves sleep or mood.
Outdoors you rarely need a meter: even winter camping days averaged about 10,000 lux across the waking day. A meter earns its place indoors, where light is far dimmer, and for checking a SAD lamp at your sitting distance. Why morning sunlight matters.
| Product | Range | Accuracy | Cosine corrected | Melanopic reading | Sensor | Price |
|---|---|---|---|---|---|---|
| Extech LT300 | Up to 400,000 lux | ±5% of reading | Yes (cosine and color corrected) | No | Remote, 30 cm coiled cable | $244 |
| Dr.meter LX1330B | 0.1–200,000 lux | ±(4% + 10 dgt) below 20,000 lux | Not stated | No | Separate probe | $45 |
| UPRtek MK350S Premium | 1–150,000 lux | JIS Class AA, DIN Class B | Not stated | Yes (melanopic lux) | Built-in spectrometer | $4,125 |
| Extech LT45 | Up to 400,000 lux | ±3% basic | Yes (cosine and color corrected) | No | Remote, coiled cable to 1.5 m | $359 |
| UNI-T UT383BT | 0–199,900 lux | ±(4% + 8) below 10,000 lux | Not stated | No | Built-in | $35 |
| Konica Minolta T-10A | 0.01–299,900 lux | Linearity ±2% ±1 digit | Yes, f2 within 3% | No | Detachable head; 1–10 m corded versions | – |
| Sekonic C-800 SpectroMaster | 1–200,000 lux | JIS C 1609-1 Class A | Not stated | No | Built-in spectrometer | $1,899 |
| URCERI SMT912 | 0–200,000 lux | ±3% rdg ±8 dgt below 10,000 lux | Claimed (f2 ≤ 2%), unverified | No | Built-in | $30 |
Prices are approximate list prices in USD at the time we checked and change often.
Best overall
by Extech · $244
Cosine- and color-corrected lux meter with a 400,000 lux range and a remote sensor on a cable. Accurate enough to check SAD lamps, desks and full sun.
RangeUp to 400,000 lux
Best for: Checking a SAD lamp, your desk and daylight with one dependable meter
Best budget
by Dr.meter · $45
The classic budget lux meter: 0.1 to 200,000 lux, a separate sensor probe, and independent test data that shows where it errs. About $45 on Amazon.
Range0.1–200,000 lux
Best for: A cheap, good-enough check of a SAD lamp or room, with readings treated as ±10%
Best for melanopic light
by UPRtek · $4,125
Handheld spectrometer that reports melanopic lux alongside lux, color temperature, CRI and flicker. The only meter here that reads body-clock light directly.
Range1–150,000 lux
Best for: Lighting designers, researchers and anyone who needs melanopic numbers, not estimates
Best for LED lamps
by Extech · $359
LED-focused lux meter with ±3% basic accuracy, cosine correction and a 1.5 m sensor cable. An independent test found it tracks a Class A reference closely.
RangeUp to 400,000 lux
Best for: Checking LED lamps and colored LED light where accuracy matters
Best with app logging
by UNI-T · $35
Pocket lux meter that sends readings to a phone app over Bluetooth. 0 to 199,900 lux, ±4% + 8 digits below 10,000 lux, about $35 on Amazon.
Range0–199,900 lux
Best for: Logging how light in a room changes across the day on a small budget
Reference-grade lux meter with cosine error within 3%, ±2% linearity and readings down to 0.01 lux. Sold by quote, aimed at labs and lighting audits.
Range0.01–299,900 lux
Best for: Labs, lighting audits and anyone calibrating cheaper meters
by Sekonic · $1,899
Photo and film spectrometer with a Class A illuminance meter, spectrum display, CRI and TM-30. It shows no melanopic value and cannot export spectra.
Range1–200,000 lux
Best for: Photographers and filmmakers who also want to see a lamp's spectrum
by URCERI · $30
The cheapest meter here at about $30, with a color display, 200,000 lux range and ±3% spec, but no independent tests and a sensor fixed in the body.
Range0–200,000 lux
Best for: A rough, very cheap check of a SAD lamp or room
A lux meter measures illuminance: how much visible light reaches its sensor, weighted by how bright it looks to the eye. For body-clock purposes it checks two things: whether your SAD lamp delivers 10,000 lux at the distance you sit, and whether your desk gets anywhere near daylight levels. A $35 to $45 meter does both.
What it cannot tell you is how strongly that light reaches the body clock. That depends on the spectrum, which needs a spectrometer. More on that below.
A 2022 expert consensus in PLoS Biology set light targets for healthy adults aged 18 to 55, measured at the eye in the vertical plane, about 1.2 m up.1
| When | Target (melanopic EDI) |
|---|---|
| Daytime | At least 250 lux |
| Evening, from 3 hours before bed | At most 10 lux |
| Sleep | At most 1 lux, as dark as possible |
The evening limit is low because the clock is sensitive. In 55 young adults, evening light of about 25 lux halved melatonin on average, and individual sensitivity varied more than 50-fold.2 An earlier study of 23 people exposed to light at night put half of the maximum melatonin suppression at roughly 90 to 110 lux.3
Daytime is where most indoor lives fall short. A bright midday sky can exceed 100,000 lux, while typical indoor lighting is around 200 lux. When 8 adults camped for a week with only natural light, their average waking light rose more than 4-fold (4,487 vs 979 lux), and their melatonin onset moved about 2 hours earlier.4
The light levels chart lists typical readings for common places, and how many lux you need goes deeper on targets.
The consensus targets use melanopic EDI, not lux. A lux meter weights light by visual sensitivity. The melanopsin cells that signal the clock respond to a different curve that peaks near 490 nm, in the blue-cyan range.1
For standard daylight (D65) the two numbers match by definition. Electric light usually gives less. Warm white LEDs of about 2,800 to 3,100 K delivered only 0.46 to 0.53 melanopic EDI per lux in one 2023 analysis.5 So a desk reading 500 lux under warm LEDs gets roughly 230 to 265 lux melanopic EDI, right at the daytime floor.
The gap can run the other way too: a blue LED therapy device measured just 51 lux, yet its melanopic lux was 34.5 times its photopic lux.6
A workable rule: under warm white LEDs, aim for about twice the melanopic target in lux. To read melanopic light directly, you need a spectrometer that reports it, such as the UPRtek MK350S Premium. For evening, the reverse applies: warm or amber bulbs cut melanopic light more than the lux reading suggests.
Light falls off fast with distance, so the 10,000 lux on the box holds only at the distance the maker specifies. When researchers measured 24 commercial light therapy devices, only 7 met all three clinical criteria: at least 7,000 lux at the recommended distance, at least 5,000 lux 6 inches off center, and an acceptable glare rating. Several gave under 5,000 lux at the recommended distance. Some sold as 10,000 lux devices reached that only at unreasonably close range.6
The SAD lamp guide covers timing and session length, and light therapy lamps compares current models.
Phone light meter apps are free and sometimes close, but you cannot tell which. In a 2022 test of 10 phones against a reference meter at 400 lux, errors ranged from 1% (Samsung Galaxy A51) to 99% (Huawei Mate 20 Lite). Three Huawei phones with the same sensor gave different results.7
Android apps read the phone’s ambient light sensor, so every app on one phone gave the same number. iPhones give apps no light sensor, so apps use the camera and results varied by app. The best pairing in that test, an iPhone 11 Pro Max running Photone with a paper diffuser over the lens, stayed within 8% of the reference across five light levels.7
Use a phone to compare rooms or spot big gaps. Do not rely on it for a SAD lamp dose unless you have checked it against a real meter.
If you get outdoors in daylight every morning, a meter adds little, because outdoor light dwarfs indoor levels. Time it with the daylight planner and read up on morning sunlight instead.
A meter does not make bright light safe. If you have bipolar disorder, an eye condition, or take a photosensitizing medication, talk to a doctor before starting light therapy.
Brown TM, Brainard GC, Cajochen C, et al. Recommendations for daytime, evening, and nighttime indoor light exposure to best support physiology, sleep, and wakefulness in healthy adults. PLoS Biol. 2022;20(3):e3001571. doi:10.1371/journal.pbio.3001571 ↩ ↩2
Phillips AJK, Vidafar P, Burns AC, et al. High sensitivity and interindividual variability in the response of the human circadian system to evening light. Proc Natl Acad Sci USA. 2019;116(24):12019-12024. doi:10.1073/pnas.1901824116 ↩
Zeitzer JM, Dijk DJ, Kronauer RE, Brown EN, Czeisler CA. Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression. J Physiol. 2000;526(3):695-702. doi:10.1111/j.1469-7793.2000.00695.x ↩
Wright KP Jr, McHill AW, Birks BR, Griffin BR, Rusterholz T, Chinoy ED. Entrainment of the human circadian clock to the natural light-dark cycle. Curr Biol. 2013;23(16):1554-1558. doi:10.1016/j.cub.2013.06.039 ↩
Trinh VQ, Bodrogi P, Khanh TQ. Determination and measurement of melanopic equivalent daylight (D65) illuminance (mEDI) in the context of smart and integrative lighting. Sensors. 2023;23(11):5000. doi:10.3390/s23115000 ↩
Oldham MA, Oldham MB, Desan PH. Commercially available phototherapy devices for treatment of depression: physical characteristics of emitted light. Psychiatr Res Clin Pract. 2019;1(2):49-57. doi:10.1176/appi.prcp.2019.20180011 ↩ ↩2
Vujica Herzog N, Dobaj P, Buchmeister B, Spindler L. Comparison between lux meter apps and illumination measuring devices. In: Katalinic B, ed. DAAAM International Scientific Book 2022. Vienna: DAAAM International; 2022:31-46. doi:10.2507/daaam.scibook.2022.03 ↩ ↩2
A bright midday sky can exceed 100,000 lux, while typical indoor lighting is around 200 lux, according to figures reported in a 2013 Current Biology study. That gap is why a week of camping raised people's average daytime light more than 4-fold.
For rough comparisons, yes. In a 2022 test of 10 phones against a reference meter at 400 lux, errors ranged from 1% to 99%, so check your phone against a real meter before trusting it for a SAD lamp.
The research dose is 10,000 lux at the eyes, and most lamps reach it only at the distance the maker specifies. Measure from where you actually sit.
No. It weights light by how bright it looks, not by its effect on the body clock. Warm white LEDs give only about half as much melanopic light per lux as daylight, so the same lux reading can mean very different things.
A 2022 expert consensus recommends at least 250 lux melanopic EDI at eye level in the daytime, no more than 10 from 3 hours before bed, and no more than 1 while you sleep.
At eye level, facing the way you look, not flat on the desk. The consensus targets are measured at the eye in the vertical plane, about 1.2 m up.
