Anybody tried to dim their Mh's

[heyitsmeagain]

Hello All,
Has anybody had any experiance with dimming their Metal Halide systems?
I have ARO electronic ballasts and ushio 10,000 k bulbs 250w's. I want to dim them to about the same level of 175's..... I beleive the 2 250's i have are too much for my 72g bow. Plus it heats up the room i have it in alot. I have the bulbs suspended at 15 inch's above the waterline and the tank is 23 inch's deep to the bottom of the tank (Glass) but only 20-18 inch's deep to the top of the deep sand bed. I am looking to keep mostly zoo's and lps coral with other sofites and mabey some sps in the future. Any comments or suggestions are welcome. Also i have thought about switching to 14,000 k bulbs...do they run cooler than 10,000 k bulbs .... heat wise not par wise.

 

[burning2nd]

nope... i dont think you can...

im sure someone will conferm that but i dont think you can alter the volts of a ballast like that

 

[Jan]

I do it with mine. I have the Coralvue dimmable ballasts though...I don't know if it could be done otherwise.

 

[Snowboarda42]

Put some Screen door mesh over the bottom of the reflector, that should dim it significantly. Only way to tell though how much is to use a Light Par Meter...

 

[Dirtsquirt]

Doesn't sound like the greatest idea ever... I'd imagine it'd kill the life expectancy of the bulbs and ballast dramatically.

Trade someone for their 175's?

-Dan

 

[heyitsmeagain]

Is their a significant amount less heat generated by 175's compared to 250's ?

 

[burning2nd]

I have the Coralvue dimmable ballasts

i think thats the point,

 

[ronj]

i have the Coralvue dimmable ballast..i was just wondering the other day how dimming the bulbs would affect them

 

[Herefishyfishy]

i was just wondering the other day how dimming the bulbs would affect them

The not-scientific answer: makes them somewhat dimmer.

Dimming
Dimming metal halide lamps requires specialized ballasts and dimming electronics. Operating metal halide lamps at less than full output, however, produces color shift and reduced lamp efficacy. For example, a metal halide lamp can be dimmed to about 40% power, but at this level it generates only about 25% of its rated lumens, and changes color in an undesirable manner.

Lamp manufacturers advise against dimming for fear of poor stability and intolerable changes of the spectrum. However, none of the lamps showed a decrease in stability, no flicker or wandering of the discharge, and the changes of the spectrum were not negligible, but certainly not dramatic. Lamps of either manufacture retain their white color, relative peak heights of spectral lines did shift, but no gaps in the spectrum occurred. Spectra taken at 50% with 30 minutes intervals coincided.

 

[cbrivkalns]

Is their a significant amount less heat generated by 175's compared to 250's ?

I don't have any personal experience with Mh, but if the bulbs/ballasts are equally efficient between the two wattages you might get a 30% reduction in heat:

(250-175)/250 = 0.3

Maybe others have better info (based on experience).

 

[burning2nd]

heat= wasted electricity