A Light Meter for Less Than $10

[bigcheese]

I'm going to Lowe's later today. If they have one, I'll treat it with Rust-Oleum NeverWet and report back.

 

[Dana Riddle]

I'm going to Lowe's later today. If they have one, I'll treat it with Rust-Oleum NeverWet and report back.

Keep us posted please. If your procedure works, I'll do the same and see how it compares to the Li-Cor's underwater measurements.

 

[SeaDweller]

Awesome! Any other light meter we could use and use your correction factors?

 

[Dana Riddle]

Awesome! Any other light meter we could use and use your correction factors?

Lots of questions here... Immersion Effect, cosine correction, spectral response, etc. So many questions, so little time

 

[SeaDweller]

Lots of questions here... Immersion Effect, cosine correction, spectral response, etc. So many questions, so little time

I guess what I should have said is those cheap “lux” meters on amazon... do they work the same where we could substitute it for what you found?

 

[Dana Riddle]

I guess what I should have said is those cheap “lux” meters on amazon... do they work the same where we could substitute it for what you found?

Hi, Let me know what particular meter you're referencing and I'll see if my little lab's budget can afford it. If so. I'll get one and test. Like your quote "This hobby has been suckin' the monet out of my pocket since 1995!!!" - same here, except it goes back to the 1960's when I saved my allowance for 14 weeks to buy a 'miracle' DynaFlo filter...

 

[bigcheese]

Keep us posted please. If your procedure works, I'll do the same and see how it compares to the Li-Cor's underwater measurements.

Hit a snag around the pH / light / moisture switch... gonna stop and grab some silicone tape ($4) for that.

 

[Jeremy Chatham]

Thats great... simply extrapolate the e coefficient at each point and get the true curve for the cheapo meter.
We had to do it in Engineering Thermodynamics all the time. Its not that difficult. I would say set the par meter as the baseline and then find the delta PAR at each point.
It looks like it would be repeatable for redundancy. That would be the true test.
Put that baby in a ziplock bag and go for it.

 

[bigcheese]

Don't know why my post this weekend didn't submit, but the NeverWet treatment was a less-than-epic fail. The tubes for soil moisture and pH didn't seal at the case properly and it was shorted in sub-5 seconds. I picked up a second meter and Flexseal clear, hope to give it a shot with the thicker stuff.

Thats great... simply extrapolate the e coefficient at each point and get the true curve for the cheapo meter.

Only one problem... the "sensor" is nothing but a small PV cell wired to the meter's coil. Silicon PV cells are sensitive across the spectrum from near-infrared to UV-A (380-1100nm).
PAR is only the radiation in wavelengths usable for photosynthesis (400-700nm). The Li-Cor and Apogee aren't sensitive to these outliers, so Dana won't even be able to measure response to those parts of the spectrum. In order to get a decent PAR measurement for all sources we'd need to build a set of optical filters to drop the outliers... if they exist (!).

Here's my thought: if I can get the waterproofing right, we'll have one caveat... lighting sources with IR and UV components (like MH, some actinics) would probably need to be excluded, the cheap-o will falsely read high. LEDs and T5s staying within those wavelengths should be somewhat accurate.

 

[Jeremy Chatham]

Don't know why my post this weekend didn't submit, but the NeverWet treatment was a less-than-epic fail. The tubes for soil moisture and pH didn't seal at the case properly and it was shorted in sub-5 seconds. I picked up a second meter and Flexseal clear, hope to give it a shot with the thicker stuff.



Only one problem... the "sensor" is nothing but a small PV cell wired to the meter's coil. Silicon PV cells are sensitive across the spectrum from near-infrared to UV-A (380-1100nm).
PAR is only the radiation in wavelengths usable for photosynthesis (400-700nm). The Li-Cor and Apogee aren't sensitive to these outliers, so Dana won't even be able to measure response to those parts of the spectrum. In order to get a decent PAR measurement for all sources we'd need to build a set of optical filters to drop the outliers... if they exist (!).

Here's my thought: if I can get the waterproofing right, we'll have one caveat... lighting sources with IR and UV components (like MH, some actinics) would probably need to be excluded, the cheap-o will falsely read high. LEDs and T5s staying within those wavelengths should be somewhat accurate.

VERY GOOD POINTS!

 

[Jeremy Chatham]

Don't know why my post this weekend didn't submit, but the NeverWet treatment was a less-than-epic fail. The tubes for soil moisture and pH didn't seal at the case properly and it was shorted in sub-5 seconds. I picked up a second meter and Flexseal clear, hope to give it a shot with the thicker stuff.



Only one problem... the "sensor" is nothing but a small PV cell wired to the meter's coil. Silicon PV cells are sensitive across the spectrum from near-infrared to UV-A (380-1100nm).
PAR is only the radiation in wavelengths usable for photosynthesis (400-700nm). The Li-Cor and Apogee aren't sensitive to these outliers, so Dana won't even be able to measure response to those parts of the spectrum. In order to get a decent PAR measurement for all sources we'd need to build a set of optical filters to drop the outliers... if they exist (!).

Here's my thought: if I can get the waterproofing right, we'll have one caveat... lighting sources with IR and UV components (like MH, some actinics) would probably need to be excluded, the cheap-o will falsely read high. LEDs and T5s staying within those wavelengths should be somewhat accurate.

VERY GOOD POINTS!

 

[Jeremy Chatham]

Don't know why my post this weekend didn't submit, but the NeverWet treatment was a less-than-epic fail. The tubes for soil moisture and pH didn't seal at the case properly and it was shorted in sub-5 seconds. I picked up a second meter and Flexseal clear, hope to give it a shot with the thicker stuff.



Only one problem... the "sensor" is nothing but a small PV cell wired to the meter's coil. Silicon PV cells are sensitive across the spectrum from near-infrared to UV-A (380-1100nm).
PAR is only the radiation in wavelengths usable for photosynthesis (400-700nm). The Li-Cor and Apogee aren't sensitive to these outliers, so Dana won't even be able to measure response to those parts of the spectrum. In order to get a decent PAR measurement for all sources we'd need to build a set of optical filters to drop the outliers... if they exist (!).

Here's my thought: if I can get the waterproofing right, we'll have one caveat... lighting sources with IR and UV components (like MH, some actinics) would probably need to be excluded, the cheap-o will falsely read high. LEDs and T5s staying within those wavelengths should be somewhat accurate.

VERY GOOD POINTS!

 

[bigcheese]

Keep us posted please. If your procedure works, I'll do the same and see how it compares to the Li-Cor's underwater measurements.

@Dana Riddle It Lives!

Build instructions a-comin'.

 

[Dana Riddle]

@Dana Riddle It Lives!

Build instructions a-comin'.

Great! Thanks!

 

[bigcheese]

Waterproofing for the 3-Way Garden Meter

OK, Cheap Meter + Cheap Waterproofing = a not so pretty final prduct, but hey... it doesn't leak!

What you'll need:

• Cheap 3-way garden meter from Lowe's, HD or ACE... $10 for the "Panacea Products" brand (HoldAll, Audubon, Garden Accents are the same)

• "Flex Seal" clear spray rubber... $13 at Lowes, maybe less if you took the Phil Swift deal on late night TV.

• some masking or painters' tape (like 1 1/2" of it)

• an X-acto knife

• a couple drops of silicone (I'm sure we all have that laying around)

Step 1: Remove the sticker around the sensor.

Step 2: Mask out the clear plastic meter area and the sensor (PV cell) itself. When masking each, keep the tape inside of the seams, not over the top of them or overlapping onto the adjoining plastic. You want to allow the flex seal to get into the seams. It should look somewhat like below:

Step 3: With the switch in the "Light" position, put a drop of silicone into the gap on either side of the switch. (I didn't figure out how deep that recess was until after the first coat, so the pics aren't exactly correct.) Wait for the silicone to dry to the touch before moving to the next step.

Step 4: First coat of flex seal. Be aware the solvents and propellants used in this stuff will react to the clear plastic, and can bleed through the masking tape if laid on too heavy (you'll see a spot on the display in the last pic where this happened). Treat it like regular spray paint... short, quick sprays and light coats will do fine. It comes out thick and bubbly, so it's kind of hard to get a smooth coat, but who cares?

Pay special attention to the seam running around the outside, the switch area and all around where you masked off, ensure the sealant gets into the cracks. Also note in the picture below, at the area where the two metal probes enter the case. Move the probes back and forth a little as you spray, getting the sealant into all 360* around the metal pieces.

Optional: Spray the metal probes as well. One looks to be copper + zinc, the other most likely aluminum + zinc. Even though contact time with saltwater will be minimal, I didn't want to chance that stuff dissolving in my water.

Step 5: After the first coat has completely dried (24 hours), apply a second coat.
Step 6: After the second coat has dried (another 24h), cut around the edges of the masking tape with an X-Acto knife. The idea here is to cut through the flex seal down to the clear plastic, so when you remove the masking tape, it doesn't pull the sealant away from the seam. Carefully remove the masking tape, clean with alcohol, and give the whole unit a RODI/FW bath to check for leaks and get rid of any residual solvent.

On the initial test, I found it to be very sensitive to its angle to the light source... 10-15* off of perpendicular cut the value by half. I may try bending the probes into a usable handle so I don't have to be a contortionist to get the probe down to the sandbed.
I tried a few different light colors, too... it seems to be sensitive across the entire spectrum.

 

[Dana Riddle]

Waterproofing for the 3-Way Garden Meter

OK, Cheap Meter + Cheap Waterproofing = a not so pretty final prduct, but hey... it doesn't leak!

What you'll need:

• Cheap 3-way garden meter from Lowe's, HD or ACE... $10 for the "Panacea Products" brand (HoldAll, Audubon, Garden Accents are the same)

• "Flex Seal" clear spray rubber... $13 at Lowes, maybe less if you took the Phil Swift deal on late night TV.

• some masking or painters' tape (like 1 1/2" of it)

• an X-acto knife

• a couple drops of silicone (I'm sure we all have that laying around)

Step 1: Remove the sticker around the sensor.

Step 2: Mask out the clear plastic meter area and the sensor (PV cell) itself. When masking each, keep the tape inside of the seams, not over the top of them or overlapping onto the adjoining plastic. You want to allow the flex seal to get into the seams. It should look somewhat like below:

Step 3: With the switch in the "Light" position, put a drop of silicone into the gap on either side of the switch. (I didn't figure out how deep that recess was until after the first coat, so the pics aren't exactly correct.) Wait for the silicone to dry to the touch before moving to the next step.

Step 4: First coat of flex seal. Be aware the solvents and propellants used in this stuff will react to the clear plastic, and can bleed through the masking tape if laid on too heavy (you'll see a spot on the display in the last pic where this happened). Treat it like regular spray paint... short, quick sprays and light coats will do fine. It comes out thick and bubbly, so it's kind of hard to get a smooth coat, but who cares?

Pay special attention to the seam running around the outside, the switch area and all around where you masked off, ensure the sealant gets into the cracks. Also note in the picture below, at the area where the two metal probes enter the case. Move the probes back and forth a little as you spray, getting the sealant into all 360* around the metal pieces.

Optional: Spray the metal probes as well. One looks to be copper + zinc, the other most likely aluminum + zinc. Even though contact time with saltwater will be minimal, I didn't want to chance that stuff dissolving in my water.

Step 5: After the first coat has completely dried (24 hours), apply a second coat.
Step 6: After the second coat has dried (another 24h), cut around the edges of the masking tape with an X-Acto knife. The idea here is to cut through the flex seal down to the clear plastic, so when you remove the masking tape, it doesn't pull the sealant away from the seam. Carefully remove the masking tape, clean with alcohol, and give the whole unit a RODI/FW bath to check for leaks and get rid of any residual solvent.

On the initial test, I found it to be very sensitive to its angle to the light source... 10-15* off of perpendicular cut the value by half. I may try bending the probes into a usable handle so I don't have to be a contortionist to get the probe down to the sandbed.
I tried a few different light colors, too... it seems to be sensitive across the entire spectrum.

Thanks! I'll try to get into the lab today and look at effects of different spectra. I've got an Orphek LED strip light and an inexpensive PAR38 LED light from Amazon to test.

 

[Steve Erekson]

Just want to thank you for this thread. While far from being a complete picture just the ability to get a rough gauge on PAR for my tank has helped me a ton.

 

[Dana Riddle]

Just want to thank you for this thread. While far from being a complete picture just the ability to get a rough gauge on PAR for my tank has helped me a ton.

Thank you for the feedback - appreciate it!

 

[Jeremy Chatham]

I'm liking this thread. I currently have a rented parmeter from BRS.

 

[KrisReef]

I acquired one of these from China ($4.46/eBay/including shipping).
Direct sunlight pegs the meter?
A gallon size ziploc bag will also work for dry 18" submersion.
The loss of light measured because of the bag is unknown, but appeared to be minimal/~zero on the bench before submersion.
I also noted that the angle of the source light (MH250w 14K) to the meter face is critical for obtaining "peak" measurements.
I agree with @Steve Erekson that this meter is helpful to measure relative amounts of light at depth in my tank.
I am disgusted with myself for not purchasing two of these meters so I could compare them side by side.
The delivery time from China was 3+ weeks.