When you’re shopping for a SAD lamp, to ensure that you receive the full therapeutic benefits of the light, there are a few important factors to consider, namely how much light it delivers and how close to the lamp you need to sit for the treatment to be effective.
First, know that the FDA does not test, approve, or regulate light-box devices. As such, you should not use one without a physician’s guidance. We based our picks on research, customer feedback, and product specifications—including optimal sitting distances—provided by manufacturers, as well as conversations with experts who study and prescribe these units.
A light box should deliver between 2,500 and 10,000 lux. A lux is a unit that measures 1 lumen per square meter. The more lux a light delivers, the less time you need to spend positioned in front of it. For most 10,000-lux lights, 30 uninterrupted minutes per day, preferably in the morning, should suffice. “If you’re going to sleep too early and want to stay awake longer, a little bit of light therapy in the afternoon can help mitigate that,” said Teodore Postolache, PhD, a professor of psychiatry at the University of Maryland School of Medicine.
We also looked at how close to each box you need to sit to score the maximum results. Light intensity is subject to the inverse square law, which says that the intensity of light falls off by the square of the distance that you move away from it. For instance, if you are 2 feet away from a light source, you see a fourfold decrease in intensity. The farther away a person is able to sit from a lamp and still receive 10,000 lux for maximum efficacy, the more flexibility they have in terms of what they can be doing and how they can be sitting during treatment. “I insist, absolutely, that any reputable, reliable manufacturer has to tell the consumer what the distance it should be from the eyes to achieve 10,000 lux,” Lewy said. “If a light box doesn’t have that information, I wouldn’t use it.”
The larger the surface of the light box, the better. In Winter Blues, Rosenthal notes that the lights “used in almost all research studies … have an illuminated surface that is at least about one foot square.” For that reason, and the fact that smaller therapeutic lamps have not undergone the same kind of rigorous study that their bigger cousins have received, we strongly recommend light boxes with the largest surfaces. (We do recommend a smaller lamp, the HappyLight Luxe, which we think is a serviceable option if you don’t have the space or budget for one of our larger picks. However, our top pick has a longer track record of efficacy in home and academic use, and in a side-by-side comparison that we performed with a commercial luxmeter, the HappyLight Luxe’s light output did not seem as strong.)
We avoided any lamps that did not have a plastic filter to remove most if not all ultraviolet waves (which are potentially harmful to the eye), and we avoided those with incandescent bulbs, which can build up a lot of heat, as well as models that used blue LEDs, as there’s still some controversy over whether blue light, which is different from blue-enriched white light (PDF), is harmful to the eyes.
Although many SAD lamps fit the above specifications, we discounted a number of them because of their high price, overly cumbersome design, too-small size, or dubious claims about features like “ion therapy.”
Because we are not qualified or equipped to evaluate SAD lamps for efficacy, we focused instead on how easy they were to use, how much space they took up on a tabletop, and whether they met their stated specs, including their total size and weight, light-face dimensions, cord lengths, and approximate light intensities. In a nonscientific test, we compared lux readings obtained with a commercial luxmeter to check for any significant inconsistencies between stated light intensities and real-world readings.
For this review, we focused on light therapy lamps. We did not consider dawn simulators, sunrise alarm clocks, or so-called light therapy glasses.