How do you know when to change MH bulbs?

[MO Will]

I think I am getting close to bulb replacement time. I have a retrofit hood, 250 watt Hamilton 14K SE with IceCap electronic ballast, and 2 x 96 watt PC.

It has been about 9 months since I changed bulbs. I know people recommend changing bulbs around this time because of spectral shift - but how does one know if it is time to change - or does everyone go by the books?

Thanks

[BurntOutReefer]

you'll start seeing hair algae growing....(IME).....
regardless, change 9~10 months (depending on daily usage)....

[hyperfocal]

There is evidence that most of the loss of output occurs within the first 6 months of a bulbs life, and then the output remains fairly constant for the next several months (or more?). Based on that, either change your bulbs every six months for maximum output (insane $$) or every couple of years (give or take). The certainly goes against the 1-year rule of thumb but at least it's backed up with data.

here's the article.

[MO Will]

Thanks for the replies

I checked out the link hyperfocal - I guess the light output is pretty consistent but does the spectrum change?

For those using the Hamilton 14K SE - how often do you recommend changing?

WIll

[hyperfocal]

Quoted from the article:

"Of course, light intensity is only part of the story. I had no way of accurately assessing the changes, if any, in the bulbs’ spectral shift. The light spectrum, however, has been found to be far less important to corals' growth than total PAR levels.20 Changes in spectrum definitely affect the aquarium inhabitants' apparent color, though, and conceivably have a longer term effect on the corals' pigmentation. These effects are somewhat subjective, though. It may be that you would want to change the bulbs before their light output requires it simply because you don’t like how they appear. So far, though, in my tank I have not seen a noticeable change in the bulbs’ color, nor has the corals’ apparent coloration deteriorated."

-- Allen Chantelois, Light Output of the Phoenix 14,000K DE MH Bulb Over Time

[Jefe12234]

Very good info from hyperfocal. I have heard that DE bulbs generally last longer than SE bulbs due to their pressurized envelope, so the test data in that article may not necessarily apply to SE bulbs. But it certainly makes you reconsider the whole one year rule. I posted my thoughts on bulb replacement in this thread as well, Bulb Life

[hyperfocal]

Absolutely, Jefe. The results from that study are pretty narrow and it's hard to apply the results to SE bulbs with any certainty. But still, I find it hard to believe that DE bulbs last 2 - 2.5x longer that SE bulbs, particularly given their brighter burn. Hopefully we'll see similar studies for other bulbs.

[MO Will]

Thanks for the replies and the link

This will be the first time I change my MH light so I am not really too sure about what I should be looking for

Will