This work presents a bibliographical review of a preventive technique to avoid weed emergence. This technique has produced contradictory results in different research work and is thus a controversial method. The photocontrol consists in sowing and doing other labour at night or covering the tools with a light-proof cover, avoiding that weed seeds receive the necessary light stimulus for germination. Firstly some theoretical aspects are described about the physiology of light dependence of weed seed germination, which is not a constant need, and the interactions between different environmental stimuli concerning light dependence. The second part is a review on the field work conducted mainly in Northern Europe and describes the weed species, whose emergence was reduced. Finally, some conclusions concerning the possible viability of this preventive technique are expressed. The main problem seems to be the irregular efficacy, which is difficult to control as it is related to the different light sensitivity between weed species influenced by soil moisture, temperature regime and aspects of the own seed physiology.