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Light therapy lamp distance calculator

Enter what your lamp is rated at and how far you sit. You get an estimate of the light reaching you and how long a comparable session takes. No signup needed.

What does your lamp say on the box?

I sit this far from the lamp

Measure from your eyes to the face of the lamp.

Light at your seatAn approximation. Lamps are wide panels, not points of light.

4,440 lux

At 45 cm from a lamp rated 10,000 lux at 30 cm.

Comparable session

About 68 minutes

Compared with

10,000 lux for 30 minutes

How the light falls off with distance

Light falls with the square of distance. About 4,440 lux at 45 cm, from a lamp rated 10,000 lux at 30 cm.07.5k15klux2,500 lux15 cm30 cm60 cm90 cm120 cmRated4,440 lux at 45 cm

The same lamp at other distances

  1. 130 cmAbout 10,000 luxAbout 30 minutes
  2. 245 cmAbout 4,440 luxAbout 68 minutesYour seat
  3. 360 cmAbout 2,500 luxAbout 2 hours
  4. 490 cmAbout 1,110 luxOver 2 hours

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Related reads: Light therapy lamps: how to choose one and when to use it, How much morning sunlight you need and Sunrise alarm clocks.

10,000 lux distance: how the estimate works

Twice as far

About a quarter of the light

Comparison session

10,000 lux for 30 minutes 1

Flagged below

2,500 lux at your seat 1,2

Learn more

A lamp's lux rating is only true at the distance it was measured. The calculator takes that rating and scales it by the square of the distance ratio: sit at 45 cm from a lamp rated 10,000 lux at 30 cm and the estimate is about 4,440 lux. It then scales a 10,000 lux, 30 minute session to your brightness, so dimmer light means a longer session, capped between 10 and 120 minutes 1.

Why this is an approximation

The square rule is exact for a point of light, and a light box is a wide glowing panel. Close to the panel, light falls off more slowly than the rule says, so the real number at your seat may be somewhat higher than this estimate up close. The angle you sit at, whether you face the lamp, and how the rating was measured all matter too.

Learn more

For a real reading, hold a lux meter, or a phone light meter app as a rough check, where your eyes are, pointed at the lamp. Treat the result here as a way to compare distances and lamps, not a measurement.

How far to sit from a light therapy box

Learn more

Start at the distance printed on the lamp, with the lamp slightly above eye level and off to one side so light reaches your eyes without you staring into it. If your desk or table puts you further back, the estimate shows what you lose and how much longer a similar session would take. For what to look for in a lamp, read our guide to choosing a light therapy lamp.

Light therapy lamp FAQ

How far should I sit from a 10,000 lux light box?

At the distance the lamp was rated at, which is printed on the box or in the manual. Many lamps are rated at 10,000 lux somewhere between 30 and 60 cm (about 12 to 24 inches). Move back and the light drops quickly: at twice the rated distance this estimate gives about a quarter of the brightness.

Why does the light drop so fast when I move back?

Light spreads out as it travels, so the same light covers a larger area further away. For a small source, brightness falls with the square of distance. A light box is a wide panel rather than a point, so up close it usually falls off a little more slowly than this estimate, and further away it behaves more like the simple rule.

How long should I sit in front of a light therapy lamp?

Sessions in lamp research are often described as 10,000 lux for about 30 minutes, and roughly 2,500 lux takes much longer for a similar amount of light. This calculator scales the time to the brightness at your seat, between 10 and 120 minutes. It is a comparison, not a prescription; follow your lamp's instructions and any advice from your clinician.

Does a lamp brighter than 10,000 lux work faster?

More lux at your eyes means more light in less time, which is why the session estimate gets shorter as you sit closer. Very bright light can be uncomfortable or glary, though, so look past the lamp rather than straight into it, and stop if it gives you headaches or eye strain.

Can I use this to treat seasonal depression?

This calculator estimates brightness; it does not tell you whether a lamp is right for any condition. If you are thinking about a lamp for low mood, seasonal or not, talk with a clinician first, especially if you have an eye condition, bipolar disorder, or take medication that makes you sensitive to light. It is wellness education, not medical advice.

References

  1. Terman M, Terman JS (2005). Light therapy for seasonal and nonseasonal depression: efficacy, protocol, safety, and side effects. CNS Spectrums, 10(8), 647-663. doi.org/10.1017/S1092852900019611
  2. Pjrek E, Friedrich ME, Cambioli L, et al. (2020). The efficacy of light therapy in the treatment of seasonal affective disorder: a meta-analysis of randomized controlled trials. Psychotherapy and Psychosomatics, 89(1), 17-24. doi.org/10.1159/000502891

This calculator is for wellness education and gives estimates, not medical advice. It does not diagnose or treat any condition, and it does not say whether a lamp is right for you. If you have an eye condition, bipolar disorder, or take medication that increases light sensitivity, talk with your health care provider before using a bright light lamp.

Light Therapy Lamp Distance Calculator | Calibrate