PAR Meter

turbosek · 11/28/2010, 06:58 PM

Can a PAR meter be effectively used to determine WHEN to change metal halide bulbs?

I know that we must pay attention to not only intensity of the light in the tank, but also to the color (or color shift) as the bulb ages.

My thought is to buy a PAR meter to see if I really need to change the bulbs at 6-12 months like the manufacturers suggest. I run 3 400W MHs on a sunrise/sunset schedule. Each bulb runs for about 6 hours per day....at different times.

One last thing...when they suggest 6-12 months per bulb...how many hours per day is that suggestion based on?

RokleM · 11/29/2010, 12:20 PM

Absolutely... positively... maybe

It really depends on the bulb, ballast, if it's correctly driven, how or if your inhabitants react to changes in light, or if you're even "saving money" after the cost of the meter.

In short, your best option is to drive the bulb as specified by the manufacture and replace as most recommend. LPS/softies seem to care a bit less about old bulbs, where you'll see a lot of SPS guys replacing early or right on schedule. Just like is "x" skimmer right for my system, everyone has slightly different requirements and there are way too many variables. The 6-12 month rules are just based on rough info with a "normal" schedule of probably 5-10 hours. Yes, you could measure PAR loss, however nothing says as of 15% loss your livestock will start dying.

One relatively easy thing you can do is put a new bulb in one of the three spots and see how drastically things have changed. For example, I just swapped out a 250w Radium bulb at 11 or so months, and there was little to no PAR or visual to my eye spectrum shift. The 250w Radium however is rated for a good 12 months, so that's not a huge surprise however.

And as mentioned, the PAR loss is important, but spectrum change is very important as well and would be yet another piece of equipment to buy if you wanted to go that route.

oscar.millan · 11/29/2010, 12:48 PM

From all the reading I've done, the two things you worry about when bulbs get old is the intensity and spectrum.

I don't believe a PAR meter alone will allow you to know when it's time to replace the bulbs. Specially when it comes to spectrum, PAR meter has no way to measure if the spectrum has changed.

jtma508 · 11/30/2010, 07:21 PM

oscar is right. There's a lot of confusion about what PAR meters measure. Essentially tthey 'count' photons with wavelengths between ~400nm (indigo-violet just above UVA) and ~700nm (deep red). That said, you'd get the same PAR value measuring a nice even spectrum white light (all wavelengths equally distributed) and a bright yellow light (which would do nothing for your tank). The PAR meter can't tell the difference.

11/28/2010, 06:58 PM	#1
turbosek Registered Member Join Date: Apr 2010 Location: Bellingham, Wa Posts: 48	PAR Meter Can a PAR meter be effectively used to determine WHEN to change metal halide bulbs? I know that we must pay attention to not only intensity of the light in the tank, but also to the color (or color shift) as the bulb ages. My thought is to buy a PAR meter to see if I really need to change the bulbs at 6-12 months like the manufacturers suggest. I run 3 400W MHs on a sunrise/sunset schedule. Each bulb runs for about 6 hours per day....at different times. One last thing...when they suggest 6-12 months per bulb...how many hours per day is that suggestion based on?

11/29/2010, 12:20 PM	#2
RokleM Registered Member Join Date: Apr 2005 Location: Greenville, SC Posts: 9,687	Absolutely... positively... maybe It really depends on the bulb, ballast, if it's correctly driven, how or if your inhabitants react to changes in light, or if you're even "saving money" after the cost of the meter. In short, your best option is to drive the bulb as specified by the manufacture and replace as most recommend. LPS/softies seem to care a bit less about old bulbs, where you'll see a lot of SPS guys replacing early or right on schedule. Just like is "x" skimmer right for my system, everyone has slightly different requirements and there are way too many variables. The 6-12 month rules are just based on rough info with a "normal" schedule of probably 5-10 hours. Yes, you could measure PAR loss, however nothing says as of 15% loss your livestock will start dying. One relatively easy thing you can do is put a new bulb in one of the three spots and see how drastically things have changed. For example, I just swapped out a 250w Radium bulb at 11 or so months, and there was little to no PAR or visual to my eye spectrum shift. The 250w Radium however is rated for a good 12 months, so that's not a huge surprise however. And as mentioned, the PAR loss is important, but spectrum change is very important as well and would be yet another piece of equipment to buy if you wanted to go that route. __________________ -Eric-

11/29/2010, 12:48 PM	#3
oscar.millan Registered Member Join Date: Aug 2007 Location: Los Angeles, CA Posts: 2,003	From all the reading I've done, the two things you worry about when bulbs get old is the intensity and spectrum. I don't believe a PAR meter alone will allow you to know when it's time to replace the bulbs. Specially when it comes to spectrum, PAR meter has no way to measure if the spectrum has changed. __________________ "Let the future tell the truth and evaluate each one according to his work and accomplishments. The present is theirs; the future, for which I really worked, is mine." -Tesla Current Tank Info: 180g mixed reef, 90g rimless cube.

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11/30/2010, 07:21 PM	#4
jtma508 Premium Member Join Date: Jan 2008 Location: MA Posts: 1,232	oscar is right. There's a lot of confusion about what PAR meters measure. Essentially tthey 'count' photons with wavelengths between ~400nm (indigo-violet just above UVA) and ~700nm (deep red). That said, you'd get the same PAR value measuring a nice even spectrum white light (all wavelengths equally distributed) and a bright yellow light (which would do nothing for your tank). The PAR meter can't tell the difference.