LUX/FC measurements to PPFD values

[Staindsoul]

I have free access to a lux/fc meter from work. I am trying to utilize that for PPFD (par) measurements, but looking online I am not getting a warm fuzzy feeling that this will work.

Looking online to find a lux/fc to PPFD calculator or conversion factor is proving difficult.

The best I have found so far is here: https://www.waveformlighting.com/horticulture/convert-lux-to-ppfd-online-calculator

The problem is the PAR range selection seems to add some approximation value because I cant "select" an AI prime Par value range. If I put lux at a value of 1000. Here is the values it provides, based on the wavelength selections:

MONOCHROMATIC 450NM LED Blue=

RED + BLUE LED 450NM/650NM LED=

RED + BLUE + WHITE=

Thoughts? Am I out of luck with a free meter?

 

[Staindsoul]

So I have some results. This is a 2'x2'x1' 30G tank. I went with the 450NM only for conversion. It appears to be the approximate spectrum. I feel like they might be inflated values. The main reason I feel that is the findings at 42W, Saxbys V2. I got 4300LUX-496PPFD an inch below the water surface. The AI prime 16 hd is 10" above the water surface. Id love to get someone's input.

I am shooting for a reef with two softies (green sinularia and green toadstool), zoanthids, cyphastrea's, and leptoseris'. So I dont need much power. Considering starting at the real low power values below and see what happens.

 

[AquaBiomics]

As I understand it, lux/lumens cannot be accurately converted to PAR without a perfect conversion factor that is specific to the mixture of wavelengths in the lights being used. Very frustrating.

My experience trying to convert lux data has been that the choice of conversion factors makes such a big difference that I'm left without any confidence in the numbers I end up with.

I ended up buying an apogee (just the probe) and hooking it up to a multimeter. Close enough to real PAR values for about $150, without any funky conversions.

 

[Staindsoul]

As I understand it, lux/lumens cannot be accurately converted to PAR without a perfect conversion factor that is specific to the mixture of wavelengths in the lights being used. Very frustrating.

My experience trying to convert lux data has been that the choice of conversion factors makes such a big difference that I'm left without any confidence in the numbers I end up with.

I ended up buying an apogee (just the probe) and hooking it up to a multimeter. Close enough to real PAR values for about $150, without any funky conversions.

That was my concern looking around online.

If AI's par curve graphic is remotely close. Its not far off of a 450NM curve shown.

I know AI says its 100PPFD at 24" depth. Im shooting for ~50PPFD on the sand bed. Between AI's claim and the findings on "real low power" i am willing to move forward. If i was throwing high end sticks or along those lines. Id reconsider.

 

[Staindsoul]

As I understand it, lux/lumens cannot be accurately converted to PAR without a perfect conversion factor that is specific to the mixture of wavelengths in the lights being used. Very frustrating.

My experience trying to convert lux data has been that the choice of conversion factors makes such a big difference that I'm left without any confidence in the numbers I end up with.

I ended up buying an apogee (just the probe) and hooking it up to a multimeter. Close enough to real PAR values for about $150, without any funky conversions.

Out of curiosity what signal type comes off the apogee?

 

[oreo54]

Out of curiosity what signal type comes off the apogee?

Depends on model...

Simplist model.
The sensor raw output is in the micro amp range which is converted to millivolts and/or digital via adc.

Like so.

PAR Sensor Multimeter Amplifier (Apogee SQ-500)

The SQ-500 sensor is the next generation PAR meter from Apogee. However, its very low signal levels prevents its use with most low-cost multimeters. This SQ-500 amplifier board allows you to directly connect and read PAR from any multimeter capable of reading 1mV in either the volt or millivolt...

blueacro.com

PAR Sensor Arduino Interface (Apogee SQ-500)

The SQ-500 sensor is the next generation PAR meter from Apogee. However, its very low signal levels prevents its use with an Arduino. This SQ-500 amplifier board allows you to directly connect and read PAR from any Arduino or other microcontroller which has an I2C (two wire) bus. On Board 16 bit...

blueacro.com

 

[Staindsoul]

we have a process meter that goes down to microamps. The apogee sensor might be the right avenue.

Thanks.

 

[oreo54]

we have a process meter that goes down to microamps. The apogee sensor might be the right avenue.

Thanks.

Quantum (PAR & ePAR) Sensors / Meters - Full-spectrum Quantum PAR Meters and Sensors - Full Spectrum Quantum Sensor Support - Apogee Instruments, Inc.

www.apogeeinstruments.com

 

[ClownWrangler]

Depends on model...

Simplist model.
The sensor raw output is in the micro amp range which is converted to millivolts and/or digital via adc.

Like so.

PAR Sensor Multimeter Amplifier (Apogee SQ-500)

The SQ-500 sensor is the next generation PAR meter from Apogee. However, its very low signal levels prevents its use with most low-cost multimeters. This SQ-500 amplifier board allows you to directly connect and read PAR from any multimeter capable of reading 1mV in either the volt or millivolt...

blueacro.com

PAR Sensor Arduino Interface (Apogee SQ-500)

The SQ-500 sensor is the next generation PAR meter from Apogee. However, its very low signal levels prevents its use with an Arduino. This SQ-500 amplifier board allows you to directly connect and read PAR from any Arduino or other microcontroller which has an I2C (two wire) bus. On Board 16 bit...

blueacro.com

Has anyone tried either of these. You would need to multiply by the correction factor for underwater measurements. I have an apogee sq-500 sensor and my old fluke 77 multimeter gives me stable readings down to 0.1mv (10 PAR units), but I'm not sure how accurate it is. Another thing I am curious about is if PWM dimmed lighting outputs will mess with the readings on a regular multimeter.

 

[oreo54]

Has anyone tried either of these. You would need to multiply by the correction factor for underwater measurements. I have an apogee sq-500 sensor and my old fluke 77 multimeter gives me stable readings down to 0.1mv (10 PAR units), but I'm not sure how accurate it is. Another thing I am curious about is if PWM dimmed lighting outputs will mess with the readings on a regular multimeter.

Pwm is commonly around 500hZ to 1 kHz.
Some manuf could use 10-100Mhz.
Quantum meters average to micromoles of photons per meter squared per second so it seems unlikely but an interesting question.
More than likely the meter averages over a much longer time than the pwm cycle so it should be accurate.

As a side note most meters average the pwm voltage. So even though it's for example 5v, at 50% duty cycle the meter will show 2.5v
O scope will show 5v to approx zero volts.

 

[ClownWrangler]

Pwm is commonly around 500hZ to 1 kHz.
Some manuf could use 10-100Mhz.
Quantum meters average to micromoles of photons per meter squared per second so it seems unlikely but an interesting question.
More than likely the meter averages over a much longer time than the pwm cycle so it should be accurate.

As a side note most meters average the pwm voltage. So even though it's for example 5v, at 50% duty cycle the meter will show 2.5v
O scope will show 5v to approx zero volts.

Thanks. I was surprised to find that I was unable to get any usable readings with my oscope directly from the apogee sensror, but i was able to with the fluke. It looks like that blueacro amplifier is just a high quality instrumentation op amp with exceptionally low dc offset error. I recall seeing a schematic of it somewhere and it looks like it has a low pass filter in the circuit. I wonder what the cutoff frequency is. I checked the spec sheet for the SQ-500 sensor and it has a response time of <1ms. Which means that you would likely see some output ripple at 1khz for a PWM light source and almost a clean square wave at the Nyquist frequency (500Hz). I'm just contemplating between the ADC model and the analog model. The only incentive I might have for the analog version would be using with the oscope to analyze the light source PWM output.

Also, using the analog amplifier along with the built in 12 bit ADC of the Seeeduino XIAO would allow for an extremely low power consumption data logger for the AQ-500. I may go that rout and add an sd card reader and OLED display.