Humans are supposed to asleep at night and be awake during the day. Blue lights, whenever possible, should be disabled at dusk. On mobile, tablet and computer, that can be done through specific apps. For your house lighting, one should acquire bulbs that do it already. Using technology close to sleep, meditating close to sleep, doing any other activity that requires intense focus (close to bed time) is going to to reduce your sleep quality. On the other hand, relaxing activities such as reading a paper book will help improve your sleep quality. Drink water at most 90 minutes before bed time or your sleep quality will be reduced and you might even have to wake up during the night and go to the toilet. Going to bed before part of the digestion is complete (the part that happens in the stomach) is again not only reducing the quality of your sleep but also interfering with proper digestion and absorption of nutrients. That's why eating late like it's tradition in Southern Italy, Spain and other countries is highly unadvised and to be prevented when possible. Two hours and a half to three are a safe bet for young people when it comes to that stomach phase of digestion.
Sleep needs are unique for everyone but generally anything between a minimum of 5 hours and a maximum of 9 hours is needed for full recovery, unless you're fighting some illness. In that case, more sleep is required.
The reason why blue light (and green light) interfere with sleep is that they mess with your pineal gland, making it believe that the sun is still up. In fact, the sun going down in nature and thus the absence of blue light is what triggers the release of the hormones that facilitate sleep. If you're constantly subjected to blue light, your endocrine system will become unbalanced and you'll never get high-quality sleep.
When using herbs in any case (this time as a sleep aid to become reaccustomed to healthy sleep patterns), remember they have little power of their own and they need to be infused with the power of the elements. Which elements you need is variable and depends on the herbs. Lemon balm is related to water and ruled by Jupiter. This means it should be infused with water energy. I'd add quintessence too to reinforce it.
Lemon balm, as a sleep aid, can be used in combination with valerian and chamomile. Before using any herb, check you're not allergic to any of them. Also, lemon balm is not indicated in case you suffer from hypothyroidism or you're pregnant (which isn't the case here :D)