I just finished testing over 35 SAD light therapy lamps! Here’s the data:
Is it OK to gaze at a 10,000 lux SAD lamp at close range, with your eyes just 10 centimetres from the lamp surface, given that on a sunny summer day, the light level is also around 10,000 lux? A SAD lamp is a rectangular illuminated panel used to treat seasonal affective disorder
I just finished testing over 35 SAD light therapy lamps! Here’s the data:
Does it exist? SAD Light therapy with 10,000 lux + Sunrise alarm combo?
How long do I need to use a Lumie bright light therapy lamp each day?
Can I use a bright light therapy lamp while doing other activities, such as reading or working?
Can bright light therapy help with seasonal mood changes or winter blues?
Videos
I still have a number of lamps to test, but since we’ve hit the gloomy season I thought I’d share this with ya’ll in case you’re in the market for one!
For those of you who want to check it out: Here’s the database!
(I now also have a list of the best SAD lamps according to my testing for those interested)
It’s hard to know who’s telling the truth about their products, this includes SAD lamps. So just like in a previous post of mine on blue-blocking glasses, I set out to objectively test these lamps with a lab-grade spectrometer!
Testing is done by placing each lamp 1 foot from the spectrometer. Readings are then taken every minute for an hour.This allows me to see what the emission spectrum is like over time since LEDs often shift (sometimes quite dramatically) as they warm up...
The following metrics were tested:
Lux
This is of course the most popular measurement for a SAD lamp. Lux is an area-based numerical value based on the spectrum of light a human is most visually sensitive to.
We often see "10,000 lux" touted as the holy grail minimum, and so many lamps claim to hit this as a sort of buzzword marketing gimmick. But...
There's nothing special about hitting a minimum of 10,000 lux, so I wouldn't be overly concerned with that number specifically.
There's a better metric for circadian effectiveness anyway...
Circadian Light
Using the spectral data collected during testing, we can calculate the circadian light from each light source.
Circadian light is similar to lux, but is spectrally weighted towards the portion of the visible spectrum most suited to activating the ipRGCs in your eye, or your circadian system.
This means that a light source that emits let's say 5,000 lux and 4,000 CLA is less effective than a lamp that emits 4,500 lux and 4,500 CLA.
When it comes to white light, these metrics track pretty well with each other, generally more lux means more CLA, but not always!
So just something to be aware of.
Lux per in²
One more thing to keep in mind with a SAD lamp is how comfortable it is, not just how bright and effective it is.
For this reason, I’ve measured each light’s radiating area and calculated the “lux per in²" from each, which gives you an idea of just how much “glare” a light source might have.
There is a better metric for circadian effectiveness anyway... then look for the standout bright lights with low glare, which at this time are the Alaska Northern Light NorthStar and the Carex Classic. These lights offer disproportionately more light output for their size than others.
I personally found that going over a Glare of around 300 starts to get a little uncomfortable. Doable but I prefer equal to or less than.
Note: This is all based on a 1-foot measurement on the brightest setting of course, so you can move things away and dim them to modulate this effect.
Other Stuff
We’ve also tested CRI, color temperature, SPDs or spectral graphs, flicker, and more!
So hopefully this resource will help you objectively find the right SAD lamp if you’re on the hunt for one!
Any suggestions or questions are welcome!
I have a SAD lamp which I use to treat my seasonal affective disorder (SAD, aka: winter depression). SAD lamps are usually powdered by fluorescent tubes or LEDs, and have an illuminated rectangular surface typically around 30 x 20 cm.
When I measure the light level of this lamp using a digital lux meter, the reading is around 10,000 lux when the meter is placed just a few centimetres from the illuminated surface.
Outside on a bright sunny summer's day in the UK, I get a similar reading of around 10,000 lux on my meter, when the meter is pointing away from the Sun.
So I wonder if I can conclude from this that it would be OK to gaze directly into the SAD lamp at close range, say 10 cm away, where the illuminated rectangular surface will fill most of my field of vision? My reasoning is that if we are exposed to 10,000 lux when we are outside in the summer, it should be OK to stare directly at a SAD lamp.
Normally SAD lamp manufacturers say to place the lamp 50 cm away.
One study found that people using SAD lamps for 6 years had no adverse ocular effects, when the light level was 10,000 lux, measured at the position of their eyes.