Par...

180galreefer · 08/16/2009, 08:56 PM

Does a PAR meter measure flux?

mukymuk · 08/16/2009, 09:13 PM

No.

greenbean36191 · 08/17/2009, 07:42 AM

Yes. PAR readings are a count of the number of photons between 400-700nm hitting a m^2/s.

serpentman · 08/17/2009, 09:24 AM

+1. However the inverse is not true. A Lux meter will not measure PAR.

mukymuk · 08/17/2009, 11:09 AM

I thought luminous flux was a measure of the perceived power of light?

serpentman · 08/17/2009, 11:26 AM

It is. However PAR gives consideration to the specific wavelengths utilized by photosynthetic organisms, lux accounts for intensity of visible light.

So I did mis-speak. Its my understanding Lux is more a function of quantity and PAR a function of quality.

mukymuk · 08/17/2009, 12:20 PM

I believe luminous flux is a weighted measure of photons according to their wavelength--as is PAR. It's just that the weights are different for each.

A lux meter would give a value that corresponds to that which a PAR meter would give for the same light source, but you can't use a PAR meter to determine luminous flux without knowledge of the spectrum of the light source. Just as you can't use a lux meter to determine PAR without knowledge of the spectrum of the light source.

I am an arm-chair physicist, so use at you're own risk.

greenbean36191 · 08/17/2009, 02:52 PM

Well, the original question was whether PAR meters measure flux, not lux. Lux, luminous flux, and PAR are all different readings, but both Lux and PAR are measurements of flux.

Luminous flux is basically a measure of the visual output of a light source. Lux is a measurement of how much of that light hits an actual surface over time. Lux is related to the luminous flux of the lighting source.

Lux and PAR are very different measurements. Lux is a measurement of the photons between 330-780 nm hitting a surface after a weighting function based on the sensitivity of human vision is applied. Basically, it's a measure of how bright something would appear to the human eye. Lux meters are most sensitive to yellow and green light and least sensitive to blue and red- the opposite of chlorophyll.

PAR is simply an unweighted count of photons between 400-700 nm hitting a surface per second. At least in theory, PAR meters see all photons in that range equally.

You can interconvert Lux and PAR readings fairly easily, but to do so you need to know conversion factors specific to the light source.

mukymuk · 08/17/2009, 03:25 PM

Alright, I see now. I took "flux" to mean "luminous flux".

180, do you really mean "flux" or are you asking if a PAR meter can be used as a substitute for a Lux meter?

CubeNoob · 08/17/2009, 04:37 PM

Written right on my Apogee MQ-200 PAR meter "Quantum Flux Meter".

That said, neither PAR nor Lux are really that great of a measurement for our hobby as pointed out above. We are really only interested in the 400-500nm wavelengths primarily for our hobby. Yes, other higher wavelengths do play minor roles (coloration/pigmentation), but for sheer photosynthesis of the zooxanthellae it is the lower range we require. With that information, coupled with the fact that knowing a PAR meter measures all wavelengths equally, doesn't tell you how good or bad the light your using actually is for corals. This is where you need a Spectrometer first, then a PAR meter to compare the spectral output. Without knowing how much of each wavelegth the light is putting out the PAR reading is almost pointless because I can make a Red MH light that puts out 2000 PAR in just the 650-700nm range and according to my PAR meter it will be the best bulb made.. but according to my corals it will be the worst.

08/16/2009, 08:56 PM	#1
180galreefer Registered Member Join Date: Jan 2009 Location: Texas Posts: 57	Par... Does a PAR meter measure flux? __________________ www.thereeftank.com/forums/f6/fish-room-addition-video-build-172151.html www.vimeo.com/user5458035 www.thereeftank.com/forums/f76/diy-dimmable-led-fixture-from-scratch-151097.html Current Tank Info: 180 Gallon In-Wall, 75 gal. Sump

08/17/2009, 07:42 AM	#3
greenbean36191 Premium Member Join Date: Jun 2003 Location: Ft. Lauderdale Posts: 10,598	Yes. PAR readings are a count of the number of photons between 400-700nm hitting a m^2/s. __________________ Some say the sun rises in the East. Some say it rises in the West. The truth must be somewhere in the middle. Current Tank Info: tore them down to move and haven't had the time or money to set them back up

08/17/2009, 09:24 AM	#4
serpentman part time superhero Join Date: Apr 2006 Location: Deep in the Heart of the Snowbelt (NE OHIO) Posts: 5,698	+1. However the inverse is not true. A Lux meter will not measure PAR. __________________ BS in Marine Bio ('96), First SW tank in 1992. Current Tank(s) 300g SPS with 90g frag tank and 40 anemone tank - decommissioned 46g LPS/Softy Cube 300g FOWLR under construction - decommissioned

08/17/2009, 11:26 AM	#6
serpentman part time superhero Join Date: Apr 2006 Location: Deep in the Heart of the Snowbelt (NE OHIO) Posts: 5,698	It is. However PAR gives consideration to the specific wavelengths utilized by photosynthetic organisms, lux accounts for intensity of visible light. So I did mis-speak. Its my understanding Lux is more a function of quantity and PAR a function of quality. __________________ BS in Marine Bio ('96), First SW tank in 1992. Current Tank(s) 300g SPS with 90g frag tank and 40 anemone tank - decommissioned 46g LPS/Softy Cube 300g FOWLR under construction - decommissioned

08/17/2009, 02:52 PM	#8
greenbean36191 Premium Member Join Date: Jun 2003 Location: Ft. Lauderdale Posts: 10,598	Well, the original question was whether PAR meters measure flux, not lux. Lux, luminous flux, and PAR are all different readings, but both Lux and PAR are measurements of flux. Luminous flux is basically a measure of the visual output of a light source. Lux is a measurement of how much of that light hits an actual surface over time. Lux is related to the luminous flux of the lighting source. Lux and PAR are very different measurements. Lux is a measurement of the photons between 330-780 nm hitting a surface after a weighting function based on the sensitivity of human vision is applied. Basically, it's a measure of how bright something would appear to the human eye. Lux meters are most sensitive to yellow and green light and least sensitive to blue and red- the opposite of chlorophyll. PAR is simply an unweighted count of photons between 400-700 nm hitting a surface per second. At least in theory, PAR meters see all photons in that range equally. You can interconvert Lux and PAR readings fairly easily, but to do so you need to know conversion factors specific to the light source. __________________ Some say the sun rises in the East. Some say it rises in the West. The truth must be somewhere in the middle. Current Tank Info: tore them down to move and haven't had the time or money to set them back up

08/16/2009, 09:13 PM	#2
mukymuk Registered Member Join Date: Aug 2009 Location: Plano, TX. Posts: 109	No.

08/17/2009, 11:09 AM	#5
mukymuk Registered Member Join Date: Aug 2009 Location: Plano, TX. Posts: 109	I thought luminous flux was a measure of the perceived power of light?

08/17/2009, 12:20 PM	#7
mukymuk Registered Member Join Date: Aug 2009 Location: Plano, TX. Posts: 109	I believe luminous flux is a weighted measure of photons according to their wavelength--as is PAR. It's just that the weights are different for each. A lux meter would give a value that corresponds to that which a PAR meter would give for the same light source, but you can't use a PAR meter to determine luminous flux without knowledge of the spectrum of the light source. Just as you can't use a lux meter to determine PAR without knowledge of the spectrum of the light source. I am an arm-chair physicist, so use at you're own risk.

08/17/2009, 03:25 PM	#9
mukymuk Registered Member Join Date: Aug 2009 Location: Plano, TX. Posts: 109	Alright, I see now. I took "flux" to mean "luminous flux". 180, do you really mean "flux" or are you asking if a PAR meter can be used as a substitute for a Lux meter?

08/17/2009, 04:37 PM	#10
CubeNoob Moved On Join Date: Jul 2009 Location: Solvang, CA Posts: 200	Written right on my Apogee MQ-200 PAR meter "Quantum Flux Meter". That said, neither PAR nor Lux are really that great of a measurement for our hobby as pointed out above. We are really only interested in the 400-500nm wavelengths primarily for our hobby. Yes, other higher wavelengths do play minor roles (coloration/pigmentation), but for sheer photosynthesis of the zooxanthellae it is the lower range we require. With that information, coupled with the fact that knowing a PAR meter measures all wavelengths equally, doesn't tell you how good or bad the light your using actually is for corals. This is where you need a Spectrometer first, then a PAR meter to compare the spectral output. Without knowing how much of each wavelegth the light is putting out the PAR reading is almost pointless because I can make a Red MH light that puts out 2000 PAR in just the 650-700nm range and according to my PAR meter it will be the best bulb made.. but according to my corals it will be the worst.