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How often should Metal Halide bulbs be replaced?

Hi folks, I've been using a 400W metal halide on the large intermediate Nepenthes grow chamber (slightly cooler by about 10*F day and night than my lowland tank). All the plants are growing very well but several of them have started to produce pitchers smaller than expected (condsidering growth of several months ago and also my current feeding schedule of every 7 days or so). I am simply equating it to fading lighting and figure it is likely due to be replaced.

How long should Metal Halide bulbs last? It has been over a year since I've begun using this bulb. I don't know how long the guy I bought the setup from had used it before I got it. I replace my fluorescent tubes every 8 -12 months but I thought MH were supposed to last longer, but how long I've no idea.

Can I use any MH tubes apropriate for plant growth or must it be something special dependent upon the ballast? Mine is a Hamilton PFO, dual control 400W remote ballast made for reef aquariums. I am using one 400W on this chamber and one over the new highland chamber - when it gets built. At the moment I am using Ushio 6500K long tube type MH but they have a nice looking 400W MH bulb at the garden center that is rounded with a warmer color temp (5500K) and is cheaper than a bulb made for growing corals (which I'm not doing anyway). My ballast is by Hamilton but is supposedly not one of those "PFO EYE" ballasts that will only use the Ushio 400W bulbs.

Thanks for any thoughts from the indoor halide growers!  
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I was under the impression they should be replaced yearly but I am only going on what I have heard.
 
Hi Josh,

MH lamps last quite long with a very small decline in output levels. At the end of life they degrade more rapid (from what I've read). The 70W MH-lamps I'm using have an average lifespan of 6000 hours. I don't know the lamps available in the US, but here in Germany we can use every 70W MH and Sodium lamp with the same ballast. They all need the same inductance. In case the seller is not sure about it try to get the datasheet of the bulb which will tell you the requirements.

Cheers Joachim
 
So if your running 14hrs a day, after one year it adds up to 5096 hours. I made a pretty good guess ;>

T
 
SO I gotta buy new bulbs for sure! Heck maybe something will flower when the light levels jump up cos it's sure the levels will be way brighter when I replace this 1-2 year old bulb!

Oh boy!
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What can I put below the lights as a shade (inside the chamber away from the bulb)? Can I just string up a shade cloth made out of a flour sack dish towel? (sort of like cheesecloth but a bit thicker).

How long do I have to leave the shade up? Do I have to take the shade off for a few hours each day for a week or two to acclimate them or...?

On the fluorescent lit tank I just switch 'em for new. I get reddening on the old leaves but that doesn't bother me as they don't burn and get crispy (cos I have the humidity set for 80-90%) they just get red and colorful. But then MH is a much more intense light...
 
Well I don't do alot of under light growing with MH/HPS.  Perhaps Jeff Shafer or Joachim could answer this better.  Perhaps a small piece of aluminum screen material to cut the light for a week or so?  I would not reduce daylength or anything.  Perhaps I am being overcautious but MH is indeed a different situation than fluorescent and I think the risk is potentially there.  

I would replace the bulb and shade lightly while monitoring the plants closely the first day for potential burning and again when removing the shade material.
 
Hi,

the efficiency of modern MH lamps and fluorescent lamps is very similar, so 400W MH lamps should have a similar effect to the plants as 400W fluorescent tubes. The spectral distribution of the MH-light is much broader and the colours are better due to this.

From the pictures of Josh's plants I would guess the new MH lamp with a colour temperature of 5500k will yield harder plants. I. e. I discussed the picture of N. ephippiata Joash posted some months ago with a friend and we both agreed, that the plant didn't looked like growing under 400W MH lamps - maybe this is an efect of the spectral distribution of the old lamp.

I won't expect too much damage from the new lamp, Nepenthes are quite hard. The light levels might be measured using the photo sensor of a camera. In case they are very big a slight shading can not hurt. Under my conditions even the soft plants from Andreas adjust to very high light levels in about three weeks time. OK, the new groth is much smaller after this procedure. ;)

Cheers Joachim
 
  • #10
Joachim, the N. ephippiata is not under 400W of metal halide lighting (yet). It's in the highland tank which has roughly 300W of compact fluorescent lighting. This lighting is also due to be replaced but I am going to build a new H/L chamber (fusca, rajah and hamata have outgrown their welcome in this one) so I will eventually be using the second channel of the dual 400W MH ballast over the new highland chamber.

Currently the only tank lit with the MH is the intermediate/lowland tank which houses things like N. maxima hybrids, truncata, eustachya, sanguineas, northiana (in a shadier part) and some other assorted hybrids.
 
  • #11
The bulbs need to be changed yearly. The company that manufactured mine stated to use them longer places a risk on the ballast and it can burn out as a result. Also the spectral efficiency declines over time. The bulbs only are good for so many "lights" so avoid turning them on and off. This will wear them out sooner.

I use a plain white plastic garbage bag, one layer thick, to cut back the light where needed, and it seems to work just fine for me.
 
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