Ratnatika , a tantric text The mental laser Dhyana is an effortless flow of the mind spontaneously directed toward the object. In other words, mental concentration lasts permanently during the whole period of meditation. The purpose of mental concentration is to keep the object before the mind's eye so to speak, and it is a static process.
Meditation takes place at a higher level of mind and implies mental dynamics.
This is the basic principle of meditation. The prevailing thought is created by concentration and the movement of the mind around that particular thought is meditation. One leads to another Concentration and meditation, even if they seem very close, are nevertheless distinct phenomena. If you realize a good concentration, this will lead automatically to meditation, because in yoga every step, when perfectly realized, gives the key to the next step. Do not force or do not try to accelerate the process of passing from concentration to meditation.