The Daylight Lantern is a simple magic item which mimics the abilities of a standard lantern, created as a lesser enchanted device for an Ars Magica covenant.
Now assuming that the creator of this didn’t want to take the easy way out, and just use a Circle spell to make an indefinite small light – I’d almost always opt for the simple ring/circle spell.
Daylight Lantern – a lantern crafted from steel, inset with a ceramic core. The lantern may be turned on and off by command word, and also by turning the lid clockwise and counter-clockwise. It provides a bright soft light equivalent to daylight which shines all around.
Shine as the Day – CrIg 18 (Base 4 for light of a cloudy day, +1 Touch, +1 Conc), 6 uses per day +3, device maintains concentration +5.
Created with Shape and Material bonus of a lamp (+7 to produce light). If being reproduced from a labtext the lantern could be created by junior wizards or perhaps an apprentice.