Thanks for the feed back man. So wrist band gadgets truly helpful to get a better sleep, because they use the concept of accupressure (might you are familiar with) which helps in greater production of melatonin- harmone responsible for sleep.

Rem sleep and Nrem sleep are two major types of sleep. Rem is considered as light sleep and whereas Nrem sleep is deep sleep because in Nrem sleep you mind is literally inactive as compared to Rem sleep.

Now lets see the stages of sleep usually 5 stages, after 3rd stage Nrem sleep occurs and after Nrem sleep the chances of Rem sleep are high. Now see the sleep patterns, first light blue means you are going from 1-3 stage, in which your body go to sleep slowly, dark blue pattern means you are now in Nrem sleep and hence in deep sleep.Then again a light pattern, probably due to Rem sleep. Now this cycle continuous and with time Nrem sleep decreases and Rem sleep increases, also shown by increase in light patterns in above picture. But also for how much time Rem sleep last and Nrem sleep occurs cannot be shown by a gadget only in my opinion. Thus they are using simple science behind it. The amount and time for Rem and Nrem sleep may vary from person to person with time. Hope you understand it.

Feel free to ask if have any further and kindly note that, that was my opinion towards wrist gadgets, may be true or.may not be...