Is there such a thing as "too much light?"

So I know someone who is currently running a 450 watt high power fluorescent fixture with a 40,000 lumen output in a 4'x2' closet grow with 4 plants. He was wondering if he adds a 600 watt HPS light (I believe its output is around 87,000 lumens) would be overkill..does anybody know anything about a lumen maximum for plants? (Heat from the HPS light is not an issue) Input is appreciated!