First, to growbe. Technically you may be right (although PAR watts don't account for differentials in energy to produce blue and red photons). But you're overcomplicating things for a grow light FAQ. If you've got lights in the correct end of the spectrum (blue light for veg growth; red light for flowering), lumen output is much, much easier to determine and almost as accurate.

The guys at Sunmaster--where you cut and pasted your info from, yes?--will give you all sorts of computations to discuss PAR watts and PPF PAR. But, realistically, the differences between that and lumen output if you're using the right bulb is fairly small...small enough so that doing the equation for PAR watts isn't worth it unless you're doing a grow over lots of square meters. And that's if you know how many PAR watts your bulb puts out; most people don't for a very good reason. Manufacturers usually don't list them. It's kind of a marketing ploy if you ask me.

Put it this way...a pretty typical 400w HPS puts out around 125 PAR watts. For top level growth, you need 135 PAR watts per sq. m.; 105 will go a good job; 75 will get you by, but you'll lose some yield. So your 400w HPS grow light will do a great job on .93 square m., a good job on 1.19 sq. m., and a mediocre job on 1.67 sq. m

But it's a lot easier to just look at the lumens...you get around 50,000 lumens from a 400w HPS. I said that 5000 lumens sq. ft./53750 a sq. m. gives you a top level grow, 4000 lumens sq. ft./43000 a sq. m. gives you a good grow, and 3000 lumens sq. ft./32250 a sq. m. gets you an okay grow with lower yields. If you use lumens instead of PAR, you get these numbers: .93 of a sq. m. for a great grow, 1.16 sq. m. for a good grow, and 1.55 sq. m. for a mediocre grow. Like I said, the difference in the calculations is small.

Still, you could argue that PAR is more exact...except very few bulb manufacturers list PAR watts for their bulbs. But almost all of them list lumens and color temp (kelvin).

So keep it simple. If you're going heavy into growth and have access to PAR watts...good for you. If you're buying your bulbs at Wal-Mart or a regular store or (my favorite) 1000bulbs.com...just go with the lumens and make sure your bulbs are in the right spectrum. To answer your question Gundari...some, but not all (or many) bulbs will list their spectrum. (Sometimes its listed like this--2700k or 2.7mk, which both stand for 2700 kelvin.) The best bet is to look at the box they came in. Barring that--lights for flowering are in the lower end of the visible spectrum. They'll look noticeably yellower or, as they say, "softer." Daylight bulbs--6500k is best--will be bright white. Hope this helps.