PAR and Dimmable Ballasts

[daylighting]

Just picked up my first HPS since '99; a 400W with dimmable ballast. I was wondering if anyone has done a spectrophotometric analysis of PAR at different settings with a digital ballast to see how PAR differs with HPS and halides. Also, if I'm running my ballast at 50%, should I use a 200W bulb or 250W?

 

[hush]

If you are running a 400w ballast at 50%, or 75% for that matter, you still need to use a 400w bulb.

 

[daylighting]

Hmmm, that's not what I've read about digital ballasts; some seem to be capable of running lower wattage bulbs when used on lower settings, and at greater efficiency too!

 

[hush]

Well the truth is that it might even be different from manufacturer to manufacturer, but "officially" the ballasts are designed to dim the full strength bulbs, while also keeping the appropriate Kelvin temperature. I personally have no idea if they will work with lower wattage bulbs, maybe they do.. But when I worked in a hydro shop the Lumatek rep told us that they are designed to dim full strength bulbs. I've just found over the years that when it comes to electronics, it's usually best to operate in the manner the manufacturer intended.

Out of curiosity, why would you not want the option of running the ballast at its full intensity?

 

[daylighting]

I agree it absolutely varies from manufacturer to manufacturer. I bought a 400W setup as it was only a few dollars more than the 250W and I figured I could use the extra wattage later, but at this time I'd rather use less power since I'm also using CFLs and LEDs. I don't really want to run over 600W for three little plants!

It also seems running higher-powered bulbs on lower power settings leads to a loss of efficiency and change in light spectrum. The digital ballast I bought is a cheapie and has 50%/75%/100% settings. I contacted the dealer for their two cents on the issue, and I'm sure they'll contact the manufacturer in turn.

 

[hush]

Right on man, go for it. At least 250s are cheaper than 400s!

 

[daylighting]

I can get no brand bulbs in both wattages for ridiculously cheap prices, but am scared to use them lol. I think I'll stick to a 250W Son-T if I try the 50% setting as I feel they'd be less likely to explode in my tent (or in my face) than the cheap Chinese ones. Just a feeling I have.

 

[joe guy]

Well they say never ever not trust your gut feeling
But if hey are that cheap get a 250 and run it at 75%
It may just run like a 250 on over drive it won't last as long
But that's with any bulb on over drive mode.. Fuck it do it in the
Name of science brothr

 

[daylighting]

I'll pass on the risk of broken glass and fire...for now at least.

Just bought a 250W Son-T. The dealer said running a 250W at 50% would work just fine!

 

[St3ve]

I have done it all. I run lower wattage bulbs at lower settings, higher wattage bulbs dimmed, and over driven bulbs and it all seems to work fine to me.

 

[DZLHIT]

If you run a 400w lamp in that ballast, and dim it to 250 you will get slightly less light than if you ran a 250w lamp.

When you under drive a bulb, the output reduction is not linear...significant? I don't know, but certainly measurable...there is a pdf somewhere around here..

When you over drive a bulb, you reduce it's life time.

 

[daylighting]

Dimming HPS bulbs (400w to 250w, for example) means you lose some red and gain more yellow. There's still some red, but you're definitely better off with a 250W bulb. I ended up going with a 250W halide instead, but since I have a plant flowering under 400W HPS, I don't wanna switch over in case it stresses it.

 

[DZLHIT]

Here is the pdf I was refering to...

View attachment LAHID.pdf