Lux Levels: How Much Light You Need, Day and Night

Lux levels outdoors dwarf indoor light. Midday sun can exceed 100,000 lux, while typical indoor lighting is around 200 lux.¹² For your body clock, experts recommend at least 250 melanopic lux at eye level during the day, no more than 10 in the 3 hours before bed, and no more than 1 while you sleep.³

What is a lux, and why is it not the whole story?

A lux is a unit of illuminance: how much visible light lands on a surface, weighted by how sensitive your eyes are to each color for seeing. A lux meter reports that number. It works well for reading, safety and office design.

Your body clock does not see light the way your vision does. It relies heavily on melanopsin, a pigment in a small group of retinal cells that responds most to blue-cyan light. In 2018 the International Commission on Illumination published CIE S 026, a standard for measuring light by its effect on these non-visual responses.⁴ The 2022 expert targets below use its melanopic metric: melanopic equivalent daylight illuminance, or melanopic EDI.³

Melanopic EDI is expressed in lux, scaled so that for daylight it roughly matches an ordinary lux reading. For warm indoor light it reads much lower. The ratio between the two is called the melanopic daylight efficacy ratio, and the 2022 consensus paper gives typical values:³

• Warm white LEDs at 2,700 to 3,000 K: below 0.35
• Fluorescent tubes at 3,000 to 4,000 K: below 0.6
• Tunable white LED at 6,500 K: about 0.83
• Daylight: about 1

So 300 lux from a warm LED might be only about 100 melanopic lux. That gap explains why a room can look bright and still be dim to your clock.

How many lux is sunlight compared with indoor light?

Outdoor light is typically at least ten times brighter than indoor light.³ The numbers below are approximate. Clouds, season, latitude and which way you face all move them a lot.

Setting	Approximate lux	What it means for your clock
Midday sun	100,000 to 130,000	Far above any indoor source12
Daylight out of direct sun	10,000 to 25,000	Strong daytime signal2
Sunrise or sunset	About 10,000	Still bright, outdoors1
Overcast day	About 1,000	Still above most indoor rooms2
Very dark overcast day	About 100	Similar to dim indoor light2
Office desk lighting	About 500 on the desk	Often below 200 melanopic lux at the eye3
Typical indoor lighting	About 200	Short of the daytime target1
Evening at home	About 20 (one small study)	Enough to affect melatonin in many people15
Twilight	About 10	Dusk-level signal2
Moonlight	About 0.1 to 0.3	Near dark12

Most people spend little time in the top half of that table. In a classic San Diego study of 106 adults aged 40 to 64, the median person spent only about 58 minutes a day above 1,000 lux.⁶ A 2023 UK study of 59 adults wearing light loggers found they averaged 2.9 hours above 250 melanopic lux between 8 am and 5 pm. On about 7% of days, they never reached it at all.⁷

The camping study by Wright and colleagues shows the size of the gap. Eight adults averaged 979 lux during waking hours on their normal routine and 4,487 lux while camping with only natural light.¹ For the morning side of this, see our guide to morning sunlight.

What lux levels do experts recommend?

In 2022, a group of circadian and sleep researchers published consensus recommendations in PLoS Biology.³ They apply to healthy adults aged 18 to 55 on regular daytime schedules, and are measured at eye level in the vertical plane, about 1.2 m up.

Time of day	Melanopic EDI at the eye	Rough lux with daylight	Rough lux with warm 2,700 to 3,000 K LED
Daytime	At least 250	250 or more	700 or more
Last 3 hours before bed	No more than 10	10 or less	About 30 or less
Sleep	No more than 1	1 or less	About 3 or less
Night, if you need to see	No more than 10	10 or less	About 30 or less

The lux columns are our arithmetic from the paper’s efficacy ratios, not figures the paper sets. Treat them as ballpark. The panel also notes that older adults may get about half the effective retinal dose because the lens yellows with age, so they may need more daytime light.³ Visual safety limits still come first.

Why 250 melanopic lux in the day?

Brighter days seem to make the clock less sensitive to light at night. In a crossover study of 12 adults, a week with about 4.3 hours a day of bright light made melatonin significantly less suppressed by 3 hours of 500 lux than a week spent in dim light, though individuals varied widely.⁸ In 32 older adults with insomnia, those who got less daytime light showed larger phase delays from evening light (correlations above 0.78).⁹

Bright daytime light also tends to raise alertness. A systematic review of 68 studies found brighter white light increased self-rated alertness in most of them. Many studies were small, though, and effects on reaction-time tests were much less consistent.¹⁰ In the UK logger study, brighter light at the time was linked with lower sleepiness, most clearly in the morning.⁷

The largest data set is observational. Among 86,772 UK Biobank adults who wore light sensors, more daytime light was linked with lower risk of depression, PTSD, psychosis and self-harm, independent of night light.¹¹ That cannot prove cause, but it points the same way as the lab work.

Why only 10 melanopic lux in the evening?

Your clock is sensitive to ordinary room light late in the day. A few numbers from controlled studies:

• In 116 healthy young adults, room light under 200 lux in the 8 hours before bed delayed melatonin onset in 99% of people and shortened melatonin duration by about 90 minutes, compared with dim light under 3 lux.¹²
• In 23 adults, about 100 lux of evening light produced half the clock delay and half the melatonin suppression seen with about 9,000 lux.¹³
• In 55 young adults, the group-level dose for 50% melatonin suppression was about 25 lux. Individuals ranged from 6 lux to 350 lux. Ten, 30 and 50 lux delayed melatonin onset by 22, 77 and 109 minutes.⁵

Real homes often exceed the limit. Across 59 homes in Melbourne, average melanopic light before bed ranged from about 4 to 77 melanopic lux, and 48% of homes were bright enough to suppress melatonin by half in an average person. Homes with LED or fluorescent lighting had about 90% more melanopic light than homes with incandescent bulbs.¹⁴ In the UK logger study, each tenfold increase in pre-bed light was linked with about 30 minutes longer to fall asleep.⁷

The practical fix is fewer, dimmer and warmer lights after dinner. Our guide to the best light color for sleep and the circadian light bulbs category cover the options.

Why 1 melanopic lux during sleep?

In a lab study of 20 healthy adults, sleeping one night with the overhead light at 100 lux raised nighttime heart rate and increased next-morning insulin resistance, compared with sleeping under 3 lux.¹⁵ In 84,790 UK Biobank adults followed for about 8 years, those in the brightest 10% for night light had about 1.5 times the risk of type 2 diabetes of the darker half (adjusted HR 1.53).¹⁶ That is association, not proof, but there is little downside to a dark room. Blackout curtains are the usual fix for streetlight.

How do you measure lux at home?

You do not need lab equipment to check whether you are in the right range. You need a reading taken the way the targets are defined.

1. Use a dedicated lux meter if you can. They measure illuminance with a sensor designed for it. Our light meters category compares options.
2. Measure at your eyes, not your desk. The targets are for the vertical plane at eye level.³ Sit where you normally sit, hold the sensor next to your face and point it where you look. A desk reading is often higher than what reaches your eyes.
3. Convert to a rough melanopic figure. A standard lux meter cannot see color. Multiply the reading by about 1 in daylight, about 0.5 under fluorescent tubes and about 0.3 under warm LEDs.³ Some spectrometers report melanopic EDI directly.
4. Take readings at the times that matter. Mid-morning at your desk, an hour before bed in the living room, and in bed with the lights off. These three numbers tell you most of what you need.
5. Check the result. Our lux levels tool interprets a reading, and the light exposure planner turns your wake time into a day-to-night light schedule.

Can you use your phone as a lux meter?

Only for rough comparisons. Phones are not built as light meters, and the error is large.

DIAL, an accredited German lighting lab, tested 7 smartphones (older models such as the iPhone 5 and Galaxy S5) with 7 light meter apps against a calibrated reference meter.¹⁷ Errors reached 113%: one phone read 1,063 lux under 500 lux. The median iPhone read about 60% low and the median Android phone about 60% high. Even identical phones with the same app disagreed, and calibrating at one level did not fix readings at others. The lab concluded that apps are not suitable even for rough estimates.

A phone still has a limited use. If it reads 40 in your living room tonight and 400 tomorrow after you switch on the ceiling light, the direction of the change is probably right even if neither number is. For absolute numbers against the targets above, use a dedicated meter.

Who should be careful with bright light?

Ordinary daylight and normal indoor lighting are not a concern for most people. Intentionally bright light, such as a light therapy lamp, needs more care for some groups:

• Bipolar disorder. In a review of 41 studies and 799 patients with bipolar depression treated with light therapy, 0.9% switched into mania and 1.4% into hypomania. The rate rose to 18.8% in the 16 patients with rapid-cycling illness.¹⁸ Use bright light only under medical supervision.
• Eye conditions and photosensitizing drugs. Talk to an eye doctor before regular bright-light sessions if you have retinal disease or take medication that increases light sensitivity.
• Shift workers. The 2022 targets explicitly exclude shift work, which needs a different schedule.³

If you plan to use a lamp in winter, our guide on how to use a SAD lamp covers distance and timing.

The short version

Get outside in daylight, even on cloudy days, since 1,000 lux outdoors still beats most rooms. Aim for at least 250 melanopic lux at your eyes during the day. Drop to warm, low light, about 30 regular lux or less, for the last 3 hours before bed. Sleep as close to dark as you can. Measure once with a real lux meter at eye level so you know where you stand.

This guide is general information, not medical advice.

Footnotes

1. 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. Current Biology. 2013;23(16):1554-1558. doi:10.1016/j.cub.2013.06.039 ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷

2. Schlyter P. Radiometry and photometry in astronomy: How bright are natural light sources? ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷

3. 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 Biology. 2022;20(3):e3001571. doi:10.1371/journal.pbio.3001571 ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰

4. International Commission on Illumination. CIE S 026/E:2018: CIE system for metrology of optical radiation for ipRGC-influenced responses to light. ↩

5. Phillips AJK, Vidafar P, Burns AC, et al. High sensitivity and interindividual variability in the response of the human circadian system to evening light. Proceedings of the National Academy of Sciences. 2019;116(24):12019-12024. doi:10.1073/pnas.1901824116 ↩ ↩²

6. Espiritu RC, Kripke DF, Ancoli-Israel S, et al. Low illumination experienced by San Diego adults: association with atypical depressive symptoms. Biological Psychiatry. 1994;35(6):403-407. doi:10.1016/0006-3223(94)90007-8 ↩

7. Didikoglu A, Mohammadian N, Johnson S, et al. Associations between light exposure and sleep timing and sleepiness while awake in a sample of UK adults in everyday life. Proceedings of the National Academy of Sciences. 2023;120(42):e2301608120. doi:10.1073/pnas.2301608120 ↩ ↩² ↩³

8. Hébert M, Martin SK, Lee C, Eastman CI. The effects of prior light history on the suppression of melatonin by light in humans. Journal of Pineal Research. 2002;33(4):198-203. doi:10.1034/j.1600-079x.2002.01885.x ↩

9. Zeitzer JM, Friedman L, Yesavage JA. Effectiveness of evening phototherapy for insomnia is reduced by bright daytime light exposure. Sleep Medicine. 2011;12(8):805-807. doi:10.1016/j.sleep.2011.02.005 ↩

10. Souman JL, Tinga AM, Te Pas SF, van Ee R, Vlaskamp BNS. Acute alerting effects of light: a systematic literature review. Behavioural Brain Research. 2018;337:228-239. doi:10.1016/j.bbr.2017.09.016 ↩

11. Burns AC, Windred DP, Rutter MK, et al. Day and night light exposure are associated with psychiatric disorders: an objective light study in >85,000 people. Nature Mental Health. 2023;1(11):853-862. doi:10.1038/s44220-023-00135-8 ↩

12. Gooley JJ, Chamberlain K, Smith KA, et al. Exposure to room light before bedtime suppresses melatonin onset and shortens melatonin duration in humans. Journal of Clinical Endocrinology and Metabolism. 2011;96(3):E463-E472. doi:10.1210/jc.2010-2098 ↩

13. Zeitzer JM, Dijk DJ, Kronauer R, Brown E, Czeisler C. Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression. Journal of Physiology. 2000;526(Pt 3):695-702. doi:10.1111/j.1469-7793.2000.00695.x ↩

14. Cain SW, McGlashan EM, Vidafar P, et al. Evening home lighting adversely impacts the circadian system and sleep. Scientific Reports. 2020;10:19110. doi:10.1038/s41598-020-75622-4 ↩

15. Mason IC, Grimaldi D, Reid KJ, et al. Light exposure during sleep impairs cardiometabolic function. Proceedings of the National Academy of Sciences. 2022;119(12):e2113290119. doi:10.1073/pnas.2113290119 ↩

16. Windred DP, Burns AC, Rutter MK, et al. Personal light exposure patterns and incidence of type 2 diabetes: analysis of 13 million hours of light sensor data and 670,000 person-years of prospective observation. Lancet Regional Health – Europe. 2024;42:100943. doi:10.1016/j.lanepe.2024.100943 ↩

17. DIAL GmbH. Luxmeter app vs. measuring device. June 23, 2022. ↩

18. Benedetti F. Rate of switch from bipolar depression into mania after morning light therapy: a historical review. Psychiatry Research. 2018;261:351-356. doi:10.1016/j.psychres.2018.01.013 ↩