For leafy greens, look for a light that covers your growing area evenly, is rated for plant growth, and can be hung at a height that keeps the plants from getting too hot.
Coverage
Check how large an area the light covers. An even spread matters more than a single very bright spot.
Distance and height
Follow the distance guidance from the manufacturer, and adjust the height as the plants grow.
Heat
Some lights produce more heat than others. Watch the leaves and the air around the plants, and adjust the light if they look scorched or the space becomes too warm.
Timer
A timer keeps the daily light period consistent, which is easier on the plants than switching the light on and off by hand.