The best lamp to cure Gelish will be the Gelish lamp.
Every product will have different amounts of photointiators in them, and so will require different outputs of uv light. As every lamp will give a different output of uv light the only way to ensure a full and proper cure is to use the lamp designed for your system.
By using a lamp from a different manufacturer, you will be at risk of service break down and also increasing your clients chances of a reaction from uncured gel.
Also check your insurance, most will insist you use the system as a whole to be covered, and this will most definitely include the lamp.
