The 5 principles of Hatha yoga was explained by the Swami Sivananda by a metaphor with a car; "The body needs proper breathing (pranayama), breathing is the life force, as a car needs proper lubrication/oil. The body needs proper exercise (asanas) to make it function properly, as a car needs a proper engine. The body needs proper diet, as car needs fuel. The body needs proper relaxation, as a car needs a radiator to cool down. The body needs positive thinking and meditation, as a car needs a responsible and learned driver."
Take into account that at that time we were not overloaded by smartphones, internet, and all sort of electronic gadgets, so the Guru did not risk any misunderstanding like we are risking today. Today i read about an article called "Thync Vibes" created in the silicon valley, pretending to "zap your brain into a state of calm or energy with only the push of a button". it 's a small triangular device placed to the side of the forehead and attach another small strip to the back of the neck or behind the ear. Using the Thync iPhone app, you adjust the intensity and duration of the session, which can range from 5 to 20 minutes. During that time, pulses of electricity will activate either your parasympathetic nervous system (the "rest and digest" system, which slows the heart rate) or your sympathetic nervous system (responsible for the "fight or flight" response), depending on whether you choose the "calm" or "energy" setting. ( For More: http://www.huffingtonpost.com/entry/brain-stimulation-thync_55b15ed7e4b0224d88319a6d?ncid=tweetlnkushpmg00000067 )
It might be a great invention for neurologic health issues, but the risk of random people using it is terrible; using an external device seeking for inner peace lacks of sense, it's like taking drugs to avoid problem, laxatives for constipation etc. ; the result is only an illusion of satisfaction, more you seek for extrnal helps more it becomes difficult to reach the results by yourself. Anyone wanting to invest in this life to an inner accomplishment of internal peace should know that the path is leading to it is rough and unwalked, but each trial will smoothen the road and it's a road that you can take only by yourself.
Props, high-tech yoga mats, apps, White noises, color therapy lights, "himalaya soul candles" are just little helpers, decorations on this road, not tools. No problem enjoying some decoration but never forget that one of the Keys opening this road is non-attachment , "Vairagya"(term used to roughly translates dispassion, detachment, or renunciation, in particular renunciation from the pains and pleasures in the material world, Maya.) and discrimination "viveka" ( Discrimination is used to make choices that bring stable tranquility).