Metal halides at lower wattages

Backreefing

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Hello I have a question for experienced metal halide users.
Can I run my metal halides at a lower wattage? Is it bad for spectrum and the bulbs or ballast?
Specifically I have 250 watt Phoenix bulbs . I have selectable ballasts. ( 150,175,250,and250superlumans )
Can I run these Phoenix bulbs at 175 watts? Will it change the spectrum of the bulbs or cause premature failure? Thx for any reply’s.
 
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KrisReef

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I don't think the 250 watt bulb will light at the lower wattage, but I've never tried that either. If it did light I think the output would be impaired at the lower wattage. Photons need energy to jump up to higher states so they can emit the light that we use them for.

But this is a question for @Dana Riddle if you want a solid answer.
 

Naso110

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If it's an older style selectable tar ballast it probably won't fire a 250w lamp if you wire it for a 175. They're not like LEDs that you can use a smaller driver, say 50w to run a 100w LED, thus extending the life by not driving it at 100% capacity. I've never actually tried it but I doubt it will light at all at 175w. HTH
 
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Backreefing

Backreefing

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I forgot to tell everybody, the reason I’m asking these weird questions about metal halide bulbs vs wattages is I’m certain my Halides are overpowering the aquarium. The only thing I can keep is acropora. Montipora, most birdsnest, Lps and softies like zoas all die . I do got a couple of hammers up against the side of the aquarium . I don’t have access to a PAR meter . Hamilton technology suggested I run the bulbs at a lower wattage. I replyed to them asking if this is safe for the bulbs. My original question to them is to suggest a part number for 150 watt ceramic mounts for my cayman fixtures .
 
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Backreefing

Backreefing

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I’m certain nutrients are ok . About 2 days ago I checked phosphate ( Hanna ulr ) it said .030 and I haven’t checked nitrates in long time . I am getting algae on the glass ever 2 days or so . I bought 5 different montipora last weekend. 4 are dead turned white then gone . This is typical is I put them on a rack high and to the side away from the light they last much longer. Since this weekend I lowered the lights time to just 5 hours a day from 7.5 . And I’m 100 % certain I don’t have pests such as MEN .
 

Dana Riddle

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Your question about using a different wattage ballast for a MH lamp is really one for an electrical engineer, but I'll give it a shot. If the lamp will even strike (light up) with a differently rated (lower wattage) ballast, it could operate at low efficiency and over-heating of the ballast could be an issue. My advice is to raise the luminaire, or shield it with fiberglass window screening. The bleaching of your corals sounds light-related, but could be due to temperature. Diagnosing tank issues from afar is always difficult, often impossible. A picture would help.
 
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Backreefing

Backreefing

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Hamilton technology emailed me about running metal halides at lower wattages . They said it would be fine and they pointed out that they sell dimmable ballasts. So I’m going to try it tonight and see if it fires up
 
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Backreefing

Backreefing

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Well it works I have my 250watt DE bulbs powered by 175 watts. They fired up normally. But the color looks slightly more blue. And it’s noticeably not as intense. Let’s see what happens.
 
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Jposch

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Yes. You can do this. Led users trying to weigh in just muddies the waters. You will get a shift in spectrum. And they are not running as efficiently. Your "lumens per watt" will be lower, but it works. If the tank seems better, then you'd be far better off replacing the bulbs with proper wattage.
That said, I have 2 150w 14000k bulbs on my 90 gallon, and the par readings are dismal. Growth has actually been great, but the highest part of any coral is only getting 75 par. 6" below the water. Lights about 10" from surface. Sand bed gets about 20-30 par. Surprisingly, nothing is really stretching for more light. It's been said many times, but halide par ≠ LED par. I've seen sps growing well at 250 par under leds, while I've seen it at 1000+ under halides, so
 

Jposch

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In the long run, you'll be better with the 250w bulbs, as the lower wattage bulb sizes are not used in any other industry much anymore, and are being phased out. And, will likely disappear before the 250w and 400w. For me, I'd rather run some some hydroponics bulbs before going to back to LEDS if it comes to it.
 
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