400 watt with mylar = 600 watt?

Is this true... I have mylar on ceiling, floor and all 4 sides
of a 3x4 room... since adding the mylar, plant has doubled
in size in one week. Should I add second 400 light for flowering
or will I be OK....

Note: My first harvest gave me only 3oz per plant in same environment with 400 and very little mylar.

Using GH nutes in hydro, static buckets with lots of bubbles.

Room is 3x4, sealed, Huge CFM air movement with use of large induction exhaust motor fan.

No CO2 stuff.... I'm lost on this concept...

Water temps at 68-70
Hygrozime in 1/4 dose as maintenance... had rot problems, fixed now.

Plant has been bent and bent, nice SOG now at 2 1/2' tall flat top. In flowing for 2 weeks now. Growing like a weed....

Q: Will a 1,000 watt or 600 watt light give me enough extra yield to justify the cost of all new lights and lamps?

400w should be good enough for that size room. If you're going to buy abother hps I'd go with a 600w.
If you're getting 3 ounces dried and cured per plant you're doind good just as is.

yeah i'd say stick to the 400 or you might run into more ventilation and heat problems if you stick to the same size room with a higher wattage.