This prism has 50 charges. While you are holding it, you can use an action to speak one of three command words to cause one of the following effects: • The first command word causes the gem to shed bright light in a 30-foot radius and dim light for an additional 30 feet. This effect doesn’t expend a charge. It lasts until you use a bonus action to repeat the command word or until you use another function of the gem. • The second command word expends 1 charge and causes the gem to fire a brilliant beam of light at one creature you can see within 60 feet of you. The creature must succeed on a DC 15 Constitution saving throw or become blinded for 1 minute. The creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. • The third command word expends 5 charges and causes the gem to flare with blinding light in a 30-foot cone originating from it. Each creature in the cone must make a saving throw as if struck by the beam created with the second command word. When all of the gem’s charges are expended, the gem becomes a nonmagical jewel worth 50 gp.
RollQuest ships the D&D 2014 SRD as a content pack, on a 5e character sheet that does the maths - roll from the sheet and let the numbers work themselves out. Free to start.