Daylight Lamps

Daylight lamps, also known as light therapy lamps, can be valuable tool to get bright light exposure at the time of your needs. Applied in the morning, they can help you

  • treat seasonal depression or less severe forms of that “winter blues” you max experience during the dark season of the year.1 See article S.A.D. for details on this.
  • advance your circadian clock to naturally become awake earlier and the morning and get tired earlier at night.2 See article light as zeitgeber for details. (If desired, you can of course also use it at night to intentionally delay your clock, before trans-meridian travel).
As both these benefits require higher light intensities than than typical indoor illumination can provide, turning on your ceiling lamp usually doesn’t do the trick. If you’ve read our article on light as zeitgeber, you might ask yourself whether just going outside wouldn’t provide even more light for your eyes? Indeed, if it’s bright outside in the early morning, go for it, no use for a lamp! That’s why seasonal depression vanishes during spring. Yet, seasonality, location or just professional demands may prevent you from getting natural light in the necessary morning hours. That’s when daylight lamps come in handy.

What’s to know?

There’s a ton of different daylight lamps on the market and oftentimes, their descriptions sound the same, too. If you’re serious about what you are doing (and you should be), the following are some important factors to consider. However, if you’re using light therapy for treating SAD, the information provided should not replace the consultation of a doctor.

Brightness

10 000 lux ≠ 10 000 lux

There is a major problem I have with daylight lamp descriptions: 10 000 lux. “A good light therapy lamp should offer 10k lux.” Yes, that is indeed the recommendation.1 However, lux is a measure of illuminance (how much light reaches your eye) and not a measure for brightness (how much light is emitted by the lamp -> measured in lumen). As illuminance exponentially decreases with distance from the light source, lux indications only make sense when accompanied by a distance, e.g. “10k lux at 20 inches” -> if you sit 20inches/50cm away from the lamp, 10k lux will reach your eye. If the distance is not provided, the offer is not serious. For most of the small devices you see on the market, it is 10-12 inches/25-30 cm, but guess what: You don’t realistically sit that close to a lamp, so what you’ll eventually get will be far less than what is advertised. To find out for yourself, you can use lightmeter smartphone apps to measure the illuminance at where your eyes will be.

UV-free

The light from the lamp should not hurt your eyes. Therefore, no ultra-violet (UV) light should be emitted by your daylight lamp. Generally, there are two different kinds of daylight lamps: Some are based on compact fluorescent lights (CFLs) and some on light emitting diodes (LEDs). CFLs do emit a portion of UV light. It is usually filtered out by a protective screen in daylight lamps, but the product description should state that for you to be sure. LEDs don’t emit significant amounts of UV light (unless explicitly designed to). However, it might give you peace of mind to still have the guarantee by the manufacturer that it’s UV free.

Irradiation Angle

Ideally, the light shines down diagonally from above with an angle of ~15°,1 for example above your monitor or on legs on the table so you can use the space underneath for breakfast. Some devices come in that design already or have legs included while others (usually cheaper ones) do not. You do not need to look directly into the light source, but have your eyes open.1

Conclusion

Daylight lamps can help you to effectively shift your circadian rhythm and alleviate symptoms of SAD. If you’re interested in getting one, make sure it really provides the desired illuminance, ideally from an angle slightly above eye level. Use the information from the article on light as zeitgeber to find out when and for how long to schedule session. To advance your circadian clock and/or treat SAD, this will be early in the morning. If you suffer under SAD, consult with a doctor for professional guidance. If you are turned off by the bulkiness or constraints that come with daylight lamps, you might also want to consider getting light therapy glasses instead, which achieve similar efficacy while allowing you to move around freely during your session.

[1] Blume, C., Garbazza, C., & Spitschan, M. (2019, September 1). Effects of light on human circadian rhythms, sleep and mood. Somnologie. Dr. Dietrich Steinkopff Verlag GmbH and Co. KG. https://doi.org/10.1007/s11818-019-00215-x

[2] Khalsa, S. B. S., Jewett, M. E., Cajochen, C., & Czeisler, C. A. (2003, June 15). A phase response curve to single bright light pulses in human subjects. Journal of Physiology. John Wiley & Sons, Ltd. https://doi.org/10.1113/jphysiol.2003.040477