How often should you change MH bulbs?

[Ann]

Thanks!

Ann

[scubadude]

I think most manufacturers suggest every 6 mos. but i think thats hogwash! You may lose a little par after 6 mos. on most bulbs but IMO they are generally good for 8-12mos. This will all vary too depending on the type of bulb, ballast and other things such as exposure etc etc. I think manufacturers just like to sell alot of bulbs! HQI bulbs supposedly have longer life. HTH

[Ninong]

Ann,

It all depends on the type of metal halide lamp. At one extreme would be the Radium 400w 20,000K HQI mogul base lamp which should probably be changed every 8-9 months, 12 months at the most, and at the other extreme would be the 250w & 400w 6500K Iwasaki mogul base lamps which can be run for 18 months if you like. The 150w 10,000K HQI DE lamps can go 18 months and the 250w 10,000K HQI DE lamps can go 14 months.

All of that is based on running them 10 hours per day. If you run them longer, replace them sooner. If you run them less, let them go a little longer between replacements.

There is also the possibility that different ballasts may affect the useful life of the same lamp. So that's another variable.

The above recommendations are sort of a rule of thumb that combines the two main variables: spectral shift and loss of intensity. In other words, do you replace your lamps when they have lost 30% of their intensity--in which case you could run them longer in most cases--or do you replace them sooner because they may have shifted their spectral distribution long before their intensity dropped by 30%.

If you post exactly what metal halide lamps you are asking about we can give you more specific advice.

Ninong

[Ann]

Well, I don't have any yet. I was just wondering how expensive it would be to maintain them. Sounds like more than I want to invest. If the bulbs weren't so expensive I might consider it!

Thanks a lot!

Ann

[Ninong]

Not all metal halide lamps are expensive. Both the 250w and 400w size Iwasakis are only $59 each. My 250w 10,000K HQI DE lamps are only $85 each. So not all of them are $129 each and require replacing every 9 months like the 20,000K Radiums.

As a matter of fact, it is cheaper to run Iwasaki metal halide lighting than comparable PAR VHO fluorescent lighting. Of course, if you start adding VHO actinics to your Iwasakis, you will run up the cost.

Regardless of which way you choose to start out, always keep in mind that you might want to add some metal halide lighting later on down the road. Depending on the size of your tank, you can still have a fantastic tank without metal halides, but metal halides may be cheaper than you think.

Good luck,

Ninong