All praise is for Allaah alone and may the salaat and the salaam be upon His Messenger and his family and his Companions…
To proceed: Indeed the light sleep in which consciousness is not fully lost does not nullify the wudhoo.
For it is indeed established that the Prophet (sal Allaahu alaiyhi wa sallam) occasionally used to delay the isha prayer until the heads of the Companions would be nodding off with sleep, then they (the Companions) would pray and they would not make the wudhoo (again).
And with Allaah is the tawfeeq. And may peace and blessings be upon our Prophet Muhammad and his family and his Companions.