When to replace a MH bulb?

[elaminator]

2 part question.........If u have the light ON for 8 hours/day, 9am to 12pm and then 6pm to 10pm, generally what's the life span on the bulb? The bulb is a 150w double ended phoenix 14k. On a daily basis, should light be on continously or with a few hour interval in between, or does that really matter?

 

[Cheetos]

2 part question.........If u have the light ON for 8 hours/day, 9am to 12pm and then 6pm to 10pm, generally what's the life span on the bulb? The bulb is a 150w double ended phoenix 14k. On a daily basis, should light be on continously or with a few hour interval in between, or does that really matter?

Does the sun take a break miday for a few hours? I think not!

 

[OceanGuy]

I leave mine on from 7 am to 5pm. I change them every 8 months unless one burns out before then. I save the remaining ones as spares.

 

[smcnally]

Does the sun take a break miday for a few hours? I think not!

I agree...I wouldn't break the light cycle like that.

 

[hans1976]

9-noon (that is 3 hrs) and then 6-10 (is 4 hrs). That is only 7 hrs a day.

I wouldn't break the cycle like that either.

 

[reefsmurf]

Reef lighting online stores say about 12 months.

Some sites say from 5000-10000 hours depending on the type of bulb and orientation (?) That's about 1.5 - 2.5 years. on a 10hour/day cycle.

According to Westinghouse lighting:

# What is the economic life of a metal halide?
Economic life usually refers to the hours of operation a lamp is designed to provide in terms of optimum light output, color quality and energy consumption. Economic life is generally defined at 60% -75% of the lamp's rated life.

From Growlights.com:
"Metal Halides produce an abundance of light in the blue spectrum. This color of light is excellent for green leafy growth and keeping plants compact. The average lifespan is about 10,000 cumulative hours. By this time the mixture of gases has become ineffective and the bulb should be replaced. The bulb will light up beyond this time but due to the gradual decline of light, it is not worth your while to wait for the bulb to finally burn out."

Who knows?

Speaking of bulbs does anyone have a spare 150W DE bulb they don't want? My main 250W fixture blew a transformer, and now my 150W that I pulled from my spare tank is on the fritz and I' not sure why, hoping it's the bulb.

 

[dz6t]

about 12 to 18 month.

Why break up the light cycle? Thanks

 

[JohnK]

My understanding is that it varies across different bulbs and the goals of the aquarist.

Generally - but not an exact rule - the higher the K temp the more frequently the bulbs need to be changed, ie 6-8 months for 20k, closer to 12 months for a 10k, and maybe up to 18 months for a 6.5K. Those are just estimates, and different brand bulbs likely have different longevity potential.

Overall (again by my understanding) bulbs shift color and lose intensity throughout their lifespan. You will not see it, as it's super gradual, but it happens.
As aquarists we tend to strive to acheive consistency and don't want to stress our corals by running a bulb too long then shocking the corals with the increased intensity of a brand new bulb (or slow their growth/health by allowing the light charestics to change a lot). We are also quite sensitive (and our corals of course) about the spectrum of the bulbs. As the bulbs age they generally get less blue along with losing intensity. These factors tend to suggest changing bulbs well within the limits of their functional lifespan (I'm defining "functional lifespan" as how long they will still fire).

The quote above from Growlights.com (I assume) is referring to horticurtical applications. It is certainly relevant, but running a MH bulb until it stops working is not what most reefkeepers want to do. For stability's sake, IMO reeftank bulbs should be replaced before they shift/fade a lot.

Just at a guess I would suggest something like 8-10 months for the average 14k bulb.

As for turning the bulbs on and off 2x per day, I can't say anything as a fact, but I suspect that that may actually shorten the bulb life, compared to running the same # of hours / day in one light cycle. I have read that repeatedly starting bulbs can negatively affect lifespan, but I can't state it as a fact as I have seen no hard data on the topic. Most people seem to set their timers so that the lights will be on when they are home. Also, some people do run lights in phases - ie 20k on for say 10 hours, then 10k light kicking in for the middle 5 hours (but this only works if you have several lights to play around with).

Just my $.02, then again I guess it's more like my $.10 as I tend to babble....

 

[Greg Hiller]

Jimmy gave you a very good answer. It's true that multiple on-off cycles will decrease bulb life, but I don't think that going from 1 on-off cycle to 2 per day is likely to make a big difference. It's true that it's not natural though for the light to be the dimmest in the middle of the day, though I don't think that's such a big deal either.

Short answer to your question.

8 hours a day for a 14 K Phoenix bulb, probably plan on changing once every 10 months or so. Earlier if you see a loss in growth.

 

[elaminator]

Thanks fellas.