Digital dimmable ballast question

**UkMedicalGrower** · 11-01-21, 07:56 PM

With the 2x 600w my temps are stuck around 27 with everything running on max so not ideal.. Question I have is if I dim one of my ballasts down to 400w will it be okay to be used with the bulb that's currently in there or do I need a 400w bulb? Thanks

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**M_C** · 11-01-21, 07:58 PM

600w to 400w seems to be fine but most manufacturers say not to dim a 600w to 250w - not sure if that's to do with spectrum shift though....

**UkMedicalGrower** · 11-01-21, 08:02 PM

Originally Posted by M_C

600w to 400w seems to be fine but most manufacturers say not to dim a 600w to 250w - not sure if that's to do with spectrum shift though....

OK thanks I'll give it a go hoepuflly drop my temps by a degree or 2, just to double check I change it to 400w whilst it's all turnt off etc

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**M_C** · 11-01-21, 08:04 PM

I've always switched mine off to change things but someone, I'm sure it was bud? was saying they do it without switching off....

**Cannabug** · 11-01-21, 08:06 PM

Originally Posted by M_C

600w to 400w seems to be fine but most manufacturers say not to dim a 600w to 250w - not sure if that's to do with spectrum shift though....

Seen you say u grow with 250w the whole way through a grow in another thread and it was in my head if you used a 250w bulb or 600w to 250w. You've just answered my thoughts MC lol

**M_C** · 11-01-21, 08:18 PM

My ballast is a Lumatek 250w dimmable ballast with 150/175/250/SL options. That said, I do have a dimmable 600w ballast & 400w bulb.... but that's another story

**GEORGE** · 11-01-21, 10:01 PM

I would get A 400 Blub, I think even though you switch the number, she still's puts out 600W on A 400 Bulb. Any way I have A ballast that you just change bulbs with out switching any thing, and I notice that even with A 400W blub, it fires up at 600Watts. JMO

**Fatty1987** · 12-01-21, 10:23 AM

I had the same thing last week.. you must use a 400 bulb with 400w and 600 bulb with 600w

I tried it myself with a 400w bulb and 600w ballast and the ballast made a strange noise when it came on and would only run for 20 mins then shut off..

I wouldn’t risk it all the manufactures say you must use the correct bulbs for the power of the ballast even with an adjusting ballast, hope this helps

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**bigbadbillybob** · 12-01-21, 01:42 PM

if you use a 600 watt bulb at 400watts, it alters the light wavelength and spectrum.
use a 400 watt lamp at 400 and a 600watt lamp at 600

**Doug Dawson** · 12-01-21, 11:47 PM

With the Vivosun 1000watt ballast the company told me to only use 1000w bulbs and just dim them as I wanted to put a 600 bulb in it for the 600 setting. Dimming them down does alter the spectrum. Take a look at this chart for change in spectrum for MH and HPS.