Lots of people feel blue when sunlight is scarce. But users of clinical-strength light boxes swear by light therapy as something that can help lift mood and make them feel more awake and energized. Not just any “happy lamp” will do, however. Experts say they must have at least 10,000 lux (a measure of light intensity), the lamp must be close enough to your face, and must be used for 20 to 30 minutes at a time. If you’ve decided it’s time to get more light into your life, here’s what to look for in a lamp.

This compact and portable model can go wherever you do, perfect if your every day is different. A variety of minute options, from 10 to 60, allows you to have it on as long as you like. Amazon

The Mayo Clinic recommends 20 to 30 minutes a day of a 10,000-lux lamp placed 16 to 24 inches away from your face. So be sure to check the light intensity settings of any model you’re looking at.

This model filters out ultraviolet rays completely, to keep your skin and eyes safe. Amazon

When ordering them online, some people are surprised by the size of the light lamps. Some models are quite large, and heavy! That’s not necessarily a bad thing—those models are often highly rated and have other desirable features, such as the ability to tilt the light to just the right angle. But if space is at a premium for you, be sure to check the dimensions carefully before you add one to your cart. Just know that you may need to sit closer to smaller models than larger ones to get the same benefit.

Thanks to its dimensions and accompanying stand, you don’t need to sit as close to this model as other smaller options. Amazon

Because light therapy is meant to mimic the sun, the ideal angle is shining down on you, and no lower than eye level. The light needs to enter your eyes to work—but you should never look directly into a lamp—so place it to your right or left (not center), allowing the rays to penetrate but not irritate.