measuring PAR using a LUX meter vs Apogee results

[Jonreefer]

So this might get lost in the Par rental thread. Just wanted to post up my test I did today.
I rented the Apogee 210 from BRS and it came in today. Someone also mentioned you can use a cheap LUX meter to get par as well by taking the LUX and divide by 60.
I bought this meter
https://www.amazon.com/gp/product/B018QLIVSC/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

I took all my PAR readings with the Apogee unit I rented first.
Then i put the LUX meter in ziplock bag and tried to hold the bag as tight as I could against the sensor to try and get a accurate reading.
At first I tried the divide by 60 and the number was WAY low. So tried a few more divisions and found using 30 was pretty much spot on with the Apogee.
Here is the numbers I got. the red are from the Apogee and the green are the LUX meter divided by 30. I checked the number a few times in each spot and the readings came back +- 10lux on the unit so close enough. I had the unit set in M mode of 20,000 LUX since my numbers didnt go above that. you may need to set it to 200,000 if you have lights turned up more.
Now this is doing it under a Radion Gen2 pro with the Diffuser panel. I am not sure if would get same results with other lights but this would probably get anyone in the ball park of PAR numbers I think.

par levels by jon duboy, on Flickr

 

[saltyfilmfolks]

Try this. Find a spot at the top of the tank.dry.
Test the lux. Find the brightest spot on the meter.
Measure the par at the top at the highest par too. Probaly the same spot.

Let me know what you get.
In lux and par.

 

[Jonreefer]

Try this. Find a spot at the top of the tank.dry.
Test the lux. Find the brightest spot on the meter.
Measure the par at the top at the highest par too. Probaly the same spot.

Let me know what you get.
In lux and par.

dead center of the tank right above the water LUX was 18,000 that is 600 par with my numbers I was using
the apogee came to 615 same spot

 

[Scrubber_steve]

I wonder how much variation there is in readings from one LUX meter to the next?

 

[Jonreefer]

I wonder how much variation there is in readings from one LUX meter to the next?

I would bet there are differences thats why I listed the exact one I bought hoping to limit the amount since I would hope they are calibrating them pretty close to each unit. Be harder to get accurate with a bunch of different vendors since they all my calibrate a little differently.

 

[saltyfilmfolks]

dead center of the tank right above the water LUX was 18,000 that is 600 par with my numbers I was using
the apogee came to 615 same spot

That should not be correct. Should be 250-400.

I wonder how much variation there is in readings from one LUX meter to the next?

Only one user has reported bad lux readings.

I have a 500 meter and a 16 meter. Both the same.

 

[saltyfilmfolks]

I would bet there are differences thats why I listed the exact one I bought hoping to limit the amount since I would hope they are calibrating them pretty close to each unit. Be harder to get accurate with a bunch of different vendors since they all my calibrate a little differently.

Calibration methods don’t vary that much.
Quality however......:oops:

 

[Jonreefer]

That should not be correct. Should be 250-400.


Only one user has reported bad lux readings.

I have a 500 meter and a 16 meter. Both the same.

guess you didnt read I was using my math that I found would match the apogee and that is taking the LUX divide by 30 and it was pretty much right in line with all the numbers the apogee spit out.
So yes 18,000 is 600 par with my numbers I was using and it matches pretty much perfect to the apogee unit getting 615

 

[Scrubber_steve]

Calibration methods don’t vary that much.
Quality however......:oops:

There should be a reasonably easy method to check the accuracy of a LUX meter at home? Like the output of a 100 watt incandescent bulb for example?

 

[saltyfilmfolks]

guess you didnt read I was using my math that I found would match the apogee and that is taking the LUX divide by 30 and it was pretty much right in line with all the numbers the apogee spit out.
So yes 18,000 is 600 par with my numbers I was using and it matches pretty much perfect to the apogee unit getting 615

Unfortunately, that’s not how it works.

The reason the conversion constant number is what it is , is due to the spectrum of the unit.
The conversion constant of a t5 is about 50 , the sun is 54.

To get 30 would not make sense

 

[saltyfilmfolks]

There should be a reasonably easy method to check the accuracy of a LUX meter at home? Like the output of a 100 watt incandescent bulb for example?

Sadly it’s complicated. You’d need the lux of a known source at a specific distance.

However , one could take the lux and par meter outside and find the conversion constant that way.
Assuming full sun no clouds.

 

[Jonreefer]

Seem to work out just fine for me since i found a calculation that would give the same exact results as the Apogee unit using the cheap little LUX unit. I feel like I had enough data points that showed that it was working out just fine for someone to use it to get them in the ballpark. If I used 60 for the LUX unit I would have been setting lights WAY to high and cooked my corals. I know going down the road I can use this and feel comfortable knowing I am setting them right since I found the calculation that matches the output of the apogee

 

[saltyfilmfolks]

Seem to work out just fine for me since i found a calculation that would give the same exact results as the Apogee unit using the cheap little LUX unit. I feel like I had enough data points that showed that it was working out just fine for someone to use it to get them in the ballpark. If I used 60 for the LUX unit I would have been setting lights WAY to high and cooked my corals. I know going down the road I can use this and feel comfortable knowing I am setting them right since I found the calculation that matches the output of the apogee

What output are you using to get that number?

You can’t just pick a number,it’s spectrum specific so I’m curious as to how you got there.
There is no 30 here.

https://www.apogeeinstruments.com/conversion-ppfd-to-lux/

 

[Jonreefer]

There also isnt LED on there. I just figured a way to match the apogee. I dont get the kickback. Because it doesnt match what you want it to be. Isnt that how new things are found by trying new stuff to see if it works. Anyway these are my results and posted everything I did to help others. If you cant accept them then i guess they dont apply to you.

 

[saltyfilmfolks]

There also isnt LED on there. I just figured a way to match the apogee. I dont get the kickback. Because it doesnt match what you want it to be. Isnt that how new things are found by trying new stuff to see if it works. Anyway these are my results and posted everything I did to help others. If you cant accept them then i guess they dont apply to you.

I didn’t mean to offend.
I’m the reason why folks using lux again.
It’s not my numbers. It’s science.

This is how I came to get the number of 60 to pass along.
It’s led.

https://www.advancedaquarist.com/2013/2/equipment

 

[Scrubber_steve]

Seem to work out just fine for me since i found a calculation that would give the same exact results as the Apogee unit using the cheap little LUX unit. I feel like I had enough data points that showed that it was working out just fine for someone to use it to get them in the ballpark. If I used 60 for the LUX unit I would have been setting lights WAY to high and cooked my corals. I know going down the road I can use this and feel comfortable knowing I am setting them right since I found the calculation that matches the output of the apogee

There also isnt LED on there. I just figured a way to match the apogee. I dont get the kickback. Because it doesnt match what you want it to be. Isnt that how new things are found by trying new stuff to see if it works. Anyway these are my results and posted everything I did to help others. If you cant accept them then i guess they dont apply to you.

It would be interesting to see if your conversion factor of 30 still applies with your light at much higher & lower settings? Do you still have the rented par meter?

 

[Jonreefer]

I still have it. Tomorrow I can pull it out and lower my lights dim. Right now my light is running at 85% so it’s ramped up high.
I also run a bluer spectrum. With all blues 100% white 12% and green and red 10%.
I will say honestly I was expecting my ration running at 65% to be to high not being needed a 20% increase in power. I guess the diffuser really cuts power. I guess I should test that to

 

[saltyfilmfolks]

The conversion number will remain the same despite the intensity.

Only changes in spectrum will effect the conversion number.

As overall intensity increases, lux and par will track equally.

I’m honestly curious if the lux meter is bad.
600 par should be closer to 36,000 lux.

 

[Jonreefer]

I checked that dry spot again directly under the light with the lux and got 18,700

 

[saltyfilmfolks]

I checked that dry spot again directly under the light with the lux and got 18,700

And still 600 par?