So you are thinking about getting some blue-blocking glasses to wear for a couple of hours before bedtime... Are they really worth it? Is this just some fad – some kind of woo-woo hippy dippy crap?

I think the evidence from research studies on blue-blocking glasses paints an overwhelming picture of the benefits. Let's take a deep dive into the studies that have been done on blocking out blue light at night.

Background science:
Blue light (around 480 nm wavelenght) hits our retinas and signals to the brain to stop the production of melatonin.  This is supposed to happen when we get up in the morning and go outside to see the sun.  Melatonin levels are then supposed to rise again when the light levels fall in the evening. Artificial light at night from our bright overhead lights, TV's, laptops, phones, and tablets all gives off a strong amount of light in the blue spectrum. This delays our melatonin levels from rising, and decreases the overall amount of melatonin created over night.  

What is the big deal with melatonin?  Not only is it a signaling molecule to our core circadian rhythm genes, it also acts as an antioxidant inside our cells and regulates insulin levels overnight. So a lack of melatonin is thought to be one reason why light at night is linked to increased rates of breast cancer and diabetes.  

Research Studies on Blue Blocking Glasses Show:

A 2009 study published in the in the journal Chronobiology International and titled "Amber lenses to block blue light and improve sleep: a randomized trial" used 20 adults who normally have trouble sleeping to test the effects of amber colored lenses to block blue light at night. Half of the participants wore the amber glasses and the other half of the group wore yellow safety glasses.  After a one week long baseline assessment, the participants wore the glasses for 3 hours before sleep for two weeks. They were instructed not to remove the glasses until they had turned out the lights each night because even a short exposure to blue light will suppress melatonin.  The results of the study showed that quality of sleep rating for those wearing the blue blocking glasses rose by about 3 points (from about 4.5 to 7.5) but there was no improvement in quality of sleep for the control group wearing yellow glasses.

TL;DR: Study showed significant improvement in sleep quality.

Next up is a 2015 study in teenagers titled "Blue Blocker Glasses as a Countermeasure for Alerting Effects of Evening Light-Emitting Diode Screen Exposure in Male Teenagers". This was a crossover study, so the part of the study group wore the blue blocking glasses for the first week with the other half of the group wearing clear glasses. The second week, the groups swapped. This study design then eliminates any disparities between the groups. The teens wore the glasses for about three hours before bedtime for several days and then participated in an in-lab study that exposed them to 3 hours of computer usage in the evening (either wearing the blue blockers or clear glasses - depending on the week).  The results of the study showed that the blue blocking glasses raised salivary melatonin levels significantly, with peak levels about 40% higher.  Interestingly, the blue blocking glasses also led to a quicker drop in melatonin levels in the morning. The study also looked at psychomotor vigilance performance and found that wearing the blue blocking glasses slowed reaction times at night. This is an expected result; you naturally have slightly slower reaction times as you get sleepy.

TL; DR: Study of teenagers show that computer use at night suppresses melatonin unless you are wearing blue blocking glasses.

Another study  titled "Protective effect of blue-light shield eyewear for adults against light pollution from self-luminous devices used at night" in 2015 had participants wear blue light blocking glasses while using back-lit LED device (table/phone) before bed. This was also a crossover study, so participants  were tested twice, once with blue blocking glasses and once with clear glasses.  The study participants wore the glasses for two hours while reading or playing games on an iPad or iPhone before going to bed (in a sleep lab) for two consecutive nights. For most participants, melatonin rose when using the blue light blocking glasses.  Note that this was not a very long study, which shows how quickly blue light blocking glasses can have an effect.

TL;DR: Study on using a backlit tablet or phone found that melatonin levels rise with blue blocking glasses (for most people) after just a night or two.

A study titled "Blue‐blocking glasses as additive treatment for mania: a randomized placebo‐controlled trial " investigated the effects of blue blocking glasses on psychiatric hospital patients with bipolar disorder who were manic.  The blue blocking group wore orange lensed glasses from 6pm until morning for seven consecutive days.  The placebo group wore glasses with clear lenses.  All patients continued with their regular medications. The study used the Young Mania Rating Scale to judge the effectiveness of the blue blocking glasses.  The overall results showed an average decrease of Mania score by 14.1 in those wearing blue blocking glasses vs an average decrease of 1.7 in those wearing clear glasses.

TL;DR: Study on bipolar patients found that they greatly improved with blue blocking glasses worn in the evenings/night for one week.

A 2017 study titled "Attenuation of short wavelengths alters sleep and the ipRGC pupil response" looked at the effect on pupil response time, sleep, and melatonin levels in 21 adults wearing blue blocking glasses from 8pm until bedtime (average was 3+ hours later) for two weeks.  (This study was done in the summer with sunset occurring around 8pm.) The participants wore activity and sleep monitors, completed sleep quality questionnaires, and had melatonin and pupil response levels measured. After two weeks of wearing the blue blocking glasses, night-time melatonin levels increased by 58% and morning melatonin levels dropped a little. Sleep quality score either improved or remained the same for everyone in the study (overall average was improved, and no one had worsened sleep quality). Pupil response time for blue light stimulus differed significantly after wearing the blue blocking glasses for two weeks.

TL;DR: Blue blocking glasses from 8pm until bedtime (after 11pm) raised melatonin levels by 58% in two weeks. Sleep improved.

The final study that I'm going to highlight here is a study titled "Wearing blue light-blocking glasses in the evening advances circadian rhythms in the patients with delayed sleep phase disorder: An open-label trial" investigated the use of blue light blocking glasses in  people who have delayed sleep phase disorder (fancy term for night owls who go to bed late at night). The study participants wore blue blocking glasses from 9pm until bedtime for 2 weeks and the results were compared with two weeks of not wearing the glasses.  By the end of the two weeks with blue blockers, the delayed sleep phase disorder patients had sleep onset time advanced by over two hours (132 minutes) and dim light melatonin onset occurred over an hour earlier (78 minutes).

TL;DR: Blue blocking glasses worn from 9pm onward for two weeks in people with 'delayed sleep phase disorder' shifted their sleep time to be two hours earlier.

Conclusion:
Lots of studies, showing the same result: improved sleep, increased melatonin production at night. There is no downside here.  Get some blue blocking glasses and sleep well!