How much light do I have

I have a very small grow in a mylar tent that's 2x4x5. I have a 250 w hps in there now but I'm wondering if I put in my other 150 watt hps in there if I would acvtually have 400 watts of light in there or is it still just going to be 250 watts??? Thanks!

you will have a total of 400W in there, but not the same lumes as a 400W.