Let’s review what we know about SAD and light.
We know that light plays a role in seasonal affective disorder. We know further that certain wavelengths of light are more potent when it comes to affecting mood.
We know that blue wavelength light is more effective than red. See, for example, Light Therapy for Seasonal Affective Disorder with Blue Narrow-Band Light-Emitting Diodes (LEDs).
We also know something about how light does this. For example, light can suppress melatonin secretion. See, for example, http://science.sciencemag.org/content/210/4475/1267.
SAD lights can be effective for artificially inducing some of the effects that natural light can have. We say some because most of these lights filter out the UV bands that can be damaging to your eyes and skin. After all UV induced DNA damage is not really what we are after when we use a SAD light.
Which SAD light to buy can often be non obvious and often you’ll be faced with choosing between lights that are basically and roughly equivalent. We can walk you through the choices of SAD lights but just realize that the choice may ultimately come down to details that have nothing to do with the light coming out of the lamp.
The light of course is the first thing you look at to eliminate the obvious bad choices but the choice between the final lights may come down to details like whether it’s battery powered or not. Whether it is portable or not, etc.