Effect of adding hps to plants in flower - +rep

I'm new to hps, getting it today. I have 5 plants in week 4 of flower that have been under T%s and are stretched pretty tall. How high does the 400w hps have to be above plant tops? I'm worried I won't have enough vertical space if they keep growing. Will adding the hps tend to slow or stop vertical growth? If not this light can be dimmed to 50% or 200w. Would the clearance for 200w be less than for 400? Thanks!

A general rule of thumb on light distance is that if it isn't too hot for the back of your hand it should be ok for plants. About a foot or so is probably ideal I'd say, but in my first grow in the basement I had a couple I had to let grow sorta to the side of the light. The reason your plants are leggy is the flourescents. They are reaching for more light. Vertical growth will likely slow (not stop) with HPS, especially if you take other steps like topping or LST. I would not dim the lights unless you absolutely have to.

Hi - You cannot dim an HPS.
You generally want about 18in - kinda depends on your hood or reflector too. Put your hand at the bud tops - if it feels hot it's too close.

This light has a digital ballast that is dimmable to 50%. I should have topped them before the got this far into flower. I don't have much room in the closet to be tying them over but I may have to try that. Thanks

just bend and tie branches down as you need to and you should be ok. any pix?

You get some height on a plant when you switch 12/12 with hps but dunno with being so far into budding

The hotter light might cause stress to your plants if you switch and have it to close , Your plants will need to harden off a bit so keep the light high for a couple of days , For sure your going to see a big change in how they grow under a HPS

If your worried about space , Just pinch or top the main stem ( Topping ) to stop the main stem growing , This allows the other branches to catch up and will give you a flatter crown

[video=youtube;QGe_WvezuAc]http://www.youtube.com/watch?v=QGe_WvezuAc&feature=related[/video]

Illegal Smile said:

This light has a digital ballast that is dimmable to 50%. I should have topped them before the got this far into flower. I don't have much room in the closet to be tying them over but I may have to try that. Thanks

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My Bad - I misread. I thought you were asking if you could use a dimmer - like a standard dimmer on your HPS. LOL

Yeah, go with tying them down - doesn't cause the stress of topping, and you can REALLY bend them without too much problem.

just bend the tops of the plants over and tie them so they are growing sideways. You do not want to dim your bulb. If you dim it, you won't get enough light for your plants to grow healthy.