A daily vespers is just simply a vespers service that falls on a weekday without a feasted saint. They are certainly more simple and “O Gladsome Light” being read is definitely a part of that. There is no entrance and “Vouchsafe” is read immediately following “O Gladsome Light.” Generally, a daily vespers is chanted more quickly.
However a daily vespers is different than a Small Vespers. A Small Vespers is the vespers service specifically served before a Vigil and can only be celebrated in conjunction with Great Vespers.
This basically solves a scheduling problem in monasteries. Vespers is usually done at 3pm, followed by dinner, then Compline. But, what if there is a Vigil? The Vigil is usually served with Compline, which would mean the 3pm time slot would be empty. This is filled by the “Small Vespers.” After the “Small Vespers” the monastics will eat, then go into Compline and begin the vigil proper.
Hope this makes sense!