How much light is to much?

I have a friend taking down her 30 gallon tank she is willing to give me her lighting to use on my 20 gallon long, is this lighting going to kill everything or be totaly awesome?
I read some where that min is 4watt per gallon so this is way over.

HQI Aquarium Light MH 150W T5 HO

You will be fine. Just hang it a bit higher off the water or add a screen between the light and the tank to reduce the light. Free is great!

Watts per gallon doesn't matter, remember, your coral have no idea what size tank they are in, just how intense the light is and how far they are from it. I don't know what you have over your tank now but you'll want to screen it or something so your corals can adjust slowly, I have a 150 watt halide over my nanocube and upgraded from a 70 watt halide, most did fine, but some of the lower light things weren't happy. You can also lower or shade corals too.

Thank you guys for the help. I don't have my person to talk to anymore he passed on a few years ago. So I'm kinda running on what I remember. And yes I will play the girl card. I forget alot of things thanks to my kids and the never ending can you drop, make, buy, why not, your mean, I hate you, I'm sorry, she did this/that, and the break my heart I love you. Busy life I lead. But I wouldn't have it anyother way. I just keep telling my self summer is almost over.

Summer is almost over!!! Don't say that. I haven't even had my boat running yet this year... grr

I fun a full blow reef with a whopping 36 watts over a 25 gallon tank. LED's

I have also done a 10 gallon with a 250 watt MH. My Long Tentacle anem grew to the size of a dinnerplate in that tank. So it truly depends on your tank, and how you take care of it.