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Can a white screen replace a light therapy lamp?

· 9 min read · The WhiteScreen.tv team

The sun low over dark hills under an orange and violet sky
Golden Hour, from our screensaver collection. Even a dull day outdoors gives more light than any screen.

This article explains the physics and summarizes published research. It is not medical advice. If you think you have seasonal affective disorder or depression, talk to a doctor or another qualified clinician.

Every autumn, people search for a free alternative to a light therapy lamp, and a full-screen white page looks like an obvious candidate. It is bright, it is white and it costs nothing. So we did the arithmetic.

The short answer is no. At full brightness and a normal viewing distance, a laptop or monitor delivers roughly 100 to 300 lux at your eyes. Light therapy for seasonal affective disorder (SAD) uses 10,000 lux. A screen falls short by a factor of about 30 to 100, and moving closer cannot close the gap.

What light therapy is, and how good the evidence is

In bright light therapy, a person sits in front of a light box every morning. The US National Institute of Mental Health describes a "very bright light box (10,000 lux) every day for about 30−45 minutes, usually first thing in the morning, from fall to spring" (NIMH). The 2016 Canadian (CANMAT) depression guidelines give the standard protocol as "10,000 lux (light intensity) for 30 minutes per day during the early morning", with response "usually seen within 1 to 3 weeks" (Ravindran et al., 2016).

The evidence is real but not perfect:

  • CANMAT rates light therapy as a first-line treatment for seasonal depression and a second-line option for mild to moderate non-seasonal depression (Ravindran et al., 2016).
  • A 2005 meta-analysis in the American Journal of Psychiatry found an effect size of 0.84 for bright light in SAD across eight studies, but also warned that "many reports of the efficacy of light therapy are not based on rigorous study designs" (Golden et al., 2005).
  • A 2020 meta-analysis of 19 randomized trials concluded that bright light "can be regarded as an effective treatment for SAD", while noting heterogeneous studies with small to medium samples and a moderate-to-high risk of bias (Pjrek et al., 2020).
  • The NHS in England says light therapy is "not usually available on the NHS as there's not enough evidence to tell whether it's effective", though "many people find it helps" (NHS).

Guidelines differ in how strongly they recommend it. They agree on the dose: about 10,000 lux at the eyes, for about half an hour, in the morning.

Lux and nits are different things

Two units get mixed up in this conversation.

Lux measures how much light lands on a surface, such as your face or your eyes. Light boxes are rated in lux at a stated distance. One medical encyclopedia describes sitting "2 feet (ft) or 60 centimeters (cm) away from the light box for about 30 minutes each day" (MedlinePlus).

Nits, or candelas per square meter, measure how bright a surface looks. Screens are rated in nits. Apple lists the MacBook Air at "500 nits brightness" and its 27-inch Studio Display at "600 nits brightness" (MacBook Air specs, Studio Display specs). Many office monitors and budget laptops are rated lower.

To get from one to the other you need geometry: how bright the screen is, how big it is, and how far away you are.

For a sense of scale, a common reference table gives about 1,000 lux on an overcast day, 10,000 to 25,000 lux in full daylight out of direct sun, and around 130,000 lux with the sun overhead (Schlyter). Workplace guidance puts adequate general lighting at 500 to 1,000 lux on the desk (CCOHS), and the light reaching your eyes indoors is usually lower than that.

The arithmetic

For a flat, evenly glowing disc of luminance L, the illuminance on its central axis is E = π × L × sin²θ, where θ is the angle from the center of your view to the disc's edge (Ivchenko, 2021). For a rectangle the idea is the same: add up the light from every part of the screen, weighted by its angle. We did that for a few real-world setups, with the screen straight in front of you and your eyes facing it:

SetupBrightnessDistanceLight at your eyes
14-inch laptop (31 x 17.5 cm)400 nits40 cmabout 120 lux
14-inch laptop500 nits30 cmabout 245 lux
27-inch monitor (60 x 34 cm)350 nits50 cmabout 215 lux
27-inch monitor600 nits50 cmabout 370 lux
Light therapy boxas directed10,000 lux

These are generous estimates. They assume the screen sends light out evenly at every angle, and most LCD panels are dimmer when viewed at an angle. Many OLED screens also dim themselves when the whole screen is white: in one review, a TV that reached 717 nits on small highlights managed "only 152 nits" on a full white screen (TFTCentral).

There is a striking detail in the 2020 meta-analysis. The trials it included compared bright light of at least 1,000 lux against "dim light (≤400 lx) or sham" (Pjrek et al., 2020). A white screen at arm's length sits inside the range those trials used as the comparison condition.

Why sitting closer does not fix it

Moving closer helps at first: our 400-nit laptop gives about 360 lux at 20 cm and about 750 lux at 10 cm. But there is a ceiling. Even an infinitely large flat panel produces at most E = π × L (Ivchenko, 2021). For a 500-nit screen that is about 1,570 lux, however close you get and however big the screen is. To reach 10,000 lux, a panel filling your whole view would need to glow at more than 3,000 nits, edge to edge, continuously. Ordinary laptops and monitors are designed for nothing like that.

Sitting with your face a hand's width from a glaring screen for half an hour is also uncomfortable, and it is not how light boxes are used. The usual instruction is the opposite: "Keep your eyes open, but do not look straight into the light source" (MedlinePlus).

If you are considering a light box

Talk to a clinician first, especially if any of these apply:

  • Bipolar disorder. "People with bipolar disorder are at risk of becoming manic if light therapy isn't used correctly" (Ohio State Wexner Medical Center).
  • Eye conditions or light-sensitizing medicines. Light therapy "might not be suitable if you have certain eye conditions or are taking some medicines that increase your sensitivity to light" (NHS). MedlinePlus lists some psoriasis medicines, antibiotics and antipsychotics as examples (MedlinePlus).
  • Side effects. CANMAT lists "eye strain, headache, agitation, nausea, and sedation" as common side effects (Ravindran et al., 2016). Using a box late in the day can also disturb sleep (Ohio State).

When choosing a box, the NHS advice is to make sure "it's bright enough (10,000 lux is standard), UV-free and has a UKCA or CE mark" (NHS). Check that the 10,000 lux figure is quoted at the distance you will actually sit.

What a white screen can do

A screen is a good light for nearby, everyday jobs. It can light your face on a video call, act as a reading or tracing light, or brighten a dark corner of a room. Our white screen and bright white screen pages are built for exactly that.

If what you want is more light in the morning, the most powerful free source is outside. Even an overcast day gives around 1,000 lux, several times what a screen can deliver, and bright daylight gives ten times more again. A morning walk, or working next to a window, does more for your light exposure than any web page. Researchers' recommendations for healthy adults also point that way: plenty of light during the day, and as little as practical in the evening and at night (Brown et al., 2022). Our article on using a screen as a night light covers the evening side.

None of this treats depression. If low mood is affecting your daily life, see a doctor. If you are thinking about suicide or are in crisis, contact your local emergency number now. In the US you can call or text 988; in the UK and Ireland, Samaritans are on 116 123, free and day or night.

Sources

More from WhiteScreen.tv: the screensaver collection and the changelog. How we source and check articles: editorial standards.