Don’t expect anything to happen in [one] 20-minute [session]; it’s not just going to go away because you put a machine on there.
When you receive a professional blue-light session, the first thing you'll notice is that the "light" is actually multiple diodes attached to a flat-panel apparatus that looks similar to the metallic sun shades that were popular in the '80s (think Magda in There's Something About Mary). You'll be fitted with a pair of protective goggles, the panels will be placed on top of your face, and then you'll percolate for about 20 to 30 minutes.
At-home blue lights aren't as strong, but they certainly have their place. Today's devices — which include standouts like the Me Clear Anti-Blemish Device and the FDA-approved Tria Acne Clearing Blue Light — can be used on milder, localised acne. For those with cystic acne, in-office treatments are best because they can be combined with prescription topicals and antibiotics. But if you're the type of person who gets minor breakouts around your period or during times of stress, at-home devices could be a good option.
If you want to see results, you've got to be ready to commit to using blue lights with the same frequency as you would any other type of skin treatment in your routine.