Direct sunlight is 32,000-132,000 lux. Lux is equal to lumens per square meter. 3'x3' is equal to 0.8364 m^2. So the dual 600W gives 180,000 lumens/0.836 m^2 = 215,200 lux. The single 1000W HPS is 173,400 lux. Tex seems to aim for much higher luminosity than sunlight. The obvious difference with sunlight is the spectrum, evenness and penetration.
I've been flirting with the idea of T5 for a while. Four bulbs per linear foot gives 54W/sq.ft. An 864W, 16-bulb T5 covers a 4'x4' area (1.5 m^2). T5 put out ~5000 lumens per 4' bulb...which works out to 80,700 total lumens; 54,000 lux at 12", 108,000 lux at 8.5", 216,000 lux at 6" (for argument's sake). So it seems T5 are on par with super intense HPS - would Tex approve? Light distribution is also virtually equal across the entire area. You can also cut bulbs - to lower light intensity without changing the colour spectrum. T5 are replacing HID in industry - they deliver more light at a lower electrical cost, with higher lumen maintenance and lower bulb replacement cost.
I now think it's proper to use initial lumens instead of mean lumens...however, lumens drop ~10% after two crops (1600 hrs).