Question about light intensity and Par

[orion7769]

Hey guys, i was reading and saw several graphics about par measurements for different HID bulbs, placed at different distances and i have a question. I'm running dimmable ballast with 600w hps bulb, that i initially started at 250 w in the seedling stage and then moved it up to 400 w when the plants develop first few leaves and gradually placed it lower till i'm around 30-2 cm from the tops. The graphs shows that 600 w hps has almost twice as much par reading then the 400 w, placed at the same distance which was 45 cm from the tops. It also shows that the difference in the readings between 400 watts bulb placed at 45 and at 60 cm is around 70% more par for the closer placed bulb. So if i apply the simply logic, 400 w placed at 30 cm will have almost exact same par reading as the 600 w placed at 45 cm. I put my ballast at 600 w for a brief moment today, to see what is the difference and i noticed that it gave the room much brighter light than the 400 w and also alot more intense heat from the bulb. So my question is, if everything else is equal, will and how the 600 w will be more productive in terms of yield and bud quality from the closer placed 400 w bulb. My tent is 1.2 x 1.2 m, but is not full. Thanks guys.

[gbauto]

With artificial lighting, intensity follows the inverse square for distance from the source. That means that if the light is twice the distance from the source, the intensity or PPFD seen at the canopy is 1/4 the amount.

I'm not a HID grower, but I've always read that dimming those fixtures is a bad idea-really screws up the spectrum of the lamp.
If you're able to dissipate the heat, I'd run it at full power and adjust the intensity by adjusting the hanging height. You'll get less of a change in intensity through the canopy versus lowering the power and dropping the fixture closer to compensate.

[MJTECH]

Remember every time you double the distance from the source you reduce the light level by a factor of four.

http://www.softschools.com/formulas/physics/inverse_square_law_formula/82/

[orion7769]

Ok guys, thanks. I put the bulb at 600w and will control the distance. Thanks !