# Using iPhone to measure LUX and possible conversion to PAR?



## Sean W. (Oct 12, 2013)

i use a lumen meter on my android Nexus 5... i figure its more accurate than eyeballing it.


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## JeffE (Oct 8, 2013)

Seems like it would be, I messed around with my programmable led and it seems semi accurate up to 13,000 Lux which would be 166 PAR. Hopefully we can see how this number is actually comparing to something like an Apogee.


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## boxboy (Jun 1, 2013)

I use that app called "Bee cam" from Android market, However I too really badly wanna know how close to the real deal this app gets. Setting up a 40B and I want it to be accurate.


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## pucksr (Jan 27, 2011)

It doesn't need to be super accurate. The biggest problem with "eyeballing" it is that your eyes measure light in a logarithmic scale while a light meter is linear. Your eyes just aren't good at determining if you "increased your par by 35%". They are great at figuring out if you increased it by 100%.


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## Hoppy (Dec 24, 2005)

The Apogee PAR meter isn't super accurate either. The spectral sensitivity of it's photodiode doesn't really match the PAR spectral range all that well. They only claim to be accurate to +/-4%, and most of our planted tank measurements are two digit measurements, 24, 35, 65, etc. PAR, not 3 digit measurements. So, if you are measuring 20 PAR, the reading can be between 19.5 and 20.5, which is +/-2.5%, just due to the limitations of the readout. Apogee provides correction factors for some kinds of light in order to meet the +/- 4% accuracy they claim. But, I doubt that any of us bothers with that.

The small mistakes we make in using the PAR meter probably contribute at least another +/-5% inaccuracy to our readings. Getting a really good PAR reading is pretty difficult.

I think we can easily get along with rounding off all of our PAR measurements to the nearest 5 - consider viewing our numbers as 10, 15, 20, 25, etc. not 11, 14, 21, etc. Based on that, converting a lux meter reading or probably using a cell phone app is good enough for our needs.


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## JerSaint (Oct 22, 2012)

Any input on decent app for iphone to get a lux measurement?


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## Sean W. (Oct 12, 2013)

JerSaint said:


> Any input on decent app for iphone to get a lux measurement?


i cant imagine there is that many, just get the one with the highest rating


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## jrill (Nov 20, 2013)

But what about taking the reading under water. I mean gosh, for $15 and a tube of silicone you can make the Hoppy meter and measure till your brain explodes.

Sent from my DROID RAZR HD using Tapatalk


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## Subtletanks91 (May 29, 2013)

I'm surprised there's no apps to read par


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## sowNreap (Jun 10, 2012)

I thought the conversion factor was to divide by 76. Did that change or have I been using wrong number? Not a real big of a deal but I just did a bunch of calculations & that's was I used. 

I might just try out one of those apps to see how it measures against my lux meter. Just gotta find the extra time. lol


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## 1987 (Jan 27, 2007)

I used it on my iphone before purchasing a par meter from Hoppy. Dividing by 76 and comparing what the par meter I have to says it was about 20 par off on average.

As a bonus I am not scared of dropping my phone into the tank, and can take readings underwater so I can position lights so I don't have dead spots.

An added bonus is you can go to the light stores/ pet shops if you are buying fixtures and figure out what your par is going to be before purchasing....

A side effect of this is I go to buy light bulbs for around the house and walk around the lighting section at Home Depot checking the par of every light they have on display


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## Hoppy (Dec 24, 2005)

There is no conversion factor from lux to PAR that works for all types of light. For the PC light I used in arriving at that 78 number, 78 worked fine. For much warmer light it would be off quite a bit. For sunlight it is off a lot. When you measure lux and convert to PAR you are getting a good enough estimate of the PAR, not an accurate measurement. But, we don't need an accurate measurement either.


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## pucksr (Jan 27, 2011)

It is mostly going to vary by color temperature and profile of the light. It shouldn't be very difficult to create a conversion table. Simply take known LEDs and other light sources at different temperatures and measure the PAR/Lux.


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## JeffE (Oct 8, 2013)

Lux ÷ Constant = µmol·m2·sec
Lux to PAR Conversion Factors
Light Source	Constant
Sunlight	54
Warm White Fluorescent	76
Cool White Fluorescent	74
URI (now UV) Actinic Fluorescent	18
URI (now UV) Daylight Fluorescent	54
Actinic/Daylight Combination	38
Philips 03 Actinic Fluorescent	40
Panasonic 6,700°K Power Compact	72
Panasonic 7,100°K / 6,700°K Combination	55
Osram Powerstar Metal Halide	57
Ushio 10,000°K Metal Halide	54
Coralife 10,000°K Metal Halide	30
Venture "Daylight" Metal Halide	46
Radium "Blue" Metal Halide	51
Fusion Sulfur Lamp	41
Westron Mercury Vapor Lamp	70
Iwasaki 6,500°K Metal Halide	

Here is a nice little table I found on a reef forum from flyyyguy. It really kind of makes it more confusing but I'm guessing the more reds and blues you have the lower the conversion factor will be? I have some LEDs that are 1/2 whites and then an even split of reds and blues so would I be closer to a 50 conversion factor or should we just leave it alone and use our own measurements as arbitrary amounts to find what works for us?


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## 1987 (Jan 27, 2007)

JeffE said:


> Lux ÷ Constant = µmol·m2·sec
> Lux to PAR Conversion Factors
> Light Source	Constant
> Sunlight	54
> ...


Yup that is where I got my 76 number from


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## fearsome (Feb 16, 2013)

I would also like to mention that the accuracy and range of your phone as a lux meter is dependent on the sensors which is dependent on which phone you have. An older phone probably will not have as much range. So someone with a PAR meter would have to try a lot of phones. But that said using lux to just get a sense of more or less light or where you are sitting is better than eye balling it in most cases. 

My evo 3D did not have anywhere near the range and sensitivity in lower light that my galaxy note 3 does.


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## creekbottom (Apr 5, 2012)

Wow, this is wildy inaccurate. I downloaded 3 different lux meter apps. One is way out to lunch compared to the other 2. I think it's time to do a Hoppy par meter.

Hoppy, when are you selling more?!


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## randpost (Feb 9, 2014)

I dropped my Nexus 5 in the tank. trying to get a water level reading. Good stuff. I wanted a red Nexus 5 anyway.


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## Hoppy (Dec 24, 2005)

creekbottom said:


> Wow, this is wildy inaccurate. I downloaded 3 different lux meter apps. One is way out to lunch compared to the other 2. I think it's time to do a Hoppy par meter.
> 
> Hoppy, when are you selling more?!


I don't plan to do any more of them. They are very easy to convert, and if you don't want to try to waterproof the sensor, it takes about 5 minutes to do the conversion. Even with waterproofing it, it takes about an hour or two at most. So, I can't really justify charging much more than the cost of the lux meter to make them, so there isn't much profit in it. And, of course, it does get boring! This is referring to http://www.plantedtank.net/forums/showthread.php?t=509705&highlight=


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## 13B-RX3 (Dec 8, 2012)

I was playing with a GPS app on my Galaxy S5 and i noticed it displayed LUX. I quickly threw it in a bag and dropped it in the tank. It measured 10,700 LUX. From the conversions i have found searching, that could be anywhere from 137-171 PAR. Does that sound about right? I have always been curious, but not enough to buy a PAR meter. I am running 4 55w PC and two T5HOs over a 75 gallon tank. I was using just the 55w PC over my old 55 gallon and everything seemed like it grew ok. With the addition of the T5HOs and the new bulb combination it is amazing how fast my DHG is growing. I'm running pressurized CO2 and was just curious if it was going to be too much light in the long run.

Thanks
Allen


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## Maryland Guppy (Dec 6, 2014)

I have been going through this conversion idea too.

Speaking to lux meters as an app compared to a real lux meter.
I have downloaded about a dozen and deleted most.
Most reliable to date I have found are:

View attachment 405978


The one labeled "Light Meter" I believe reads too high.

Chart by JE is great but no LED's are listed.
Web search for LED PAR data is out there though.


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## 13B-RX3 (Dec 8, 2012)

I just downloaded the Lumens Measurement app and it reads the exact same LUX as the reading on the GPS app i used.


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## 1987 (Jan 27, 2007)

13B-RX3 said:


> I was playing with a GPS app on my Galaxy S5 and i noticed it displayed LUX. I quickly threw it in a bag and dropped it in the tank. It measured 10,700 LUX. From the conversions i have found searching, that could be anywhere from 137-171 PAR. Does that sound about right? I have always been curious, but not enough to buy a PAR meter. I am running 4 55w PC and two T5HOs over a 75 gallon tank. I was using just the 55w PC over my old 55 gallon and everything seemed like it grew ok. With the addition of the T5HOs and the new bulb combination it is amazing how fast my DHG is growing. I'm running pressurized CO2 and was just curious if it was going to be too much light in the long run.
> 
> Thanks
> Allen





13B-RX3 said:


> I was playing with a GPS app on my Galaxy S5 and i noticed it displayed LUX. I quickly threw it in a bag and dropped it in the tank. It measured 10,700 LUX. From the conversions i have found searching, that could be anywhere from 137-171 PAR. Does that sound about right? I have always been curious, but not enough to buy a PAR meter. I am running 4 55w PC and two T5HOs over a 75 gallon tank. I was using just the 55w PC over my old 55 gallon and everything seemed like it grew ok. With the addition of the T5HOs and the new bulb combination it is amazing how fast my DHG is growing. I'm running pressurized CO2 and was just curious if it was going to be too much light in the long run.
> 
> Thanks
> Allen


How far down did you read 137-171? par falls off the deeper you go. Give us a depth of inches from the lights that you had those readings.


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## 13B-RX3 (Dec 8, 2012)

I set the phone on the center of the tank, laying on the substrate, and the lights are on top of the tank. Somewhere in the 20" range. The T5 bulbs are generic "plant" bulbs that have a pink color, two 460nm Actinic bulbs, and 2 10k bulbs. It looks a little odd bit you can almost watch the DHG grow, it's amazing.

Here is a pic from the day it was filled to yesterday. Just over of 2 weeks.


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## 1987 (Jan 27, 2007)

with 6 bulb 54 w HO in my reef tank I'm pulling about 170 at the bottom of the tank (bare bottom)

That is a mix of blue that don't output as much par as the daylights I have in the fixture. 

Also subtract your substrate height from your tank height.

My tank is 21" High so I think the numbers might be off. I would estimate it is probably in the 75ish range. Pcs don't push must at that depth but the ho would help


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## mistergreen (Dec 9, 2006)

It'll be fun but don't expect accuracy. It depends on the photosensitive chip with too much uv or whatever spectrum, basically will vary from device to device.


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## Maryland Guppy (Dec 6, 2014)

I've got to give credit to everyone.
I am a returning aquarist from 1986(last tank).

We all realize WPG doesn't cut it.
We are using readily available technology to get in the ball park.
I'll give an A+ to everyone just for general awareness and observation.

I'll also bet plants are doing better. :icon_smil


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## jeffkrol (Jun 5, 2013)

mistergreen said:


> It'll be fun but don't expect accuracy. It depends on the photosensitive chip with too much uv or whatever spectrum, basically will vary from device to device.
> 
> 
> Sent from my iPad using Tapatalk HD


Normally the CMOS camera sensor pack includes a hot mirror filter or high/low cutoff filter..








Anything above 700-ish is filtered out so you don't get "x-ray" cameras..









IF the app just reads the green (luminous) channel it is almost a perfect LUX meter:









as I said, very little IR gets through, which is why IR photographers have the hot mirror filter removed..

Above is a CCD sensor, which, theoretically makes a pretty darn good PAR sensor (I contemplated using one in a home brew) using just a IR/UV cut filter like the Baader..


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## mistergreen (Dec 9, 2006)

jeffkrol said:


> Normally the CMOS camera sensor pack includes a hot mirror filter or high/low cutoff filter..
> 
> 
> 
> ...



Yeah, you're right. I remember reading people hacking phone cams to shoot IR by removing the filter.

Who uses ccd cams?

I think iPhones uses back lit cmos. I read not all cmos are created equally so I think the "it varies" statement stands. 

When I have time, I can make a par app for the iPhone and see. I have an apogee par sensor I can use to test. Hoppy also researched correcting the spectral curve with light filters which I have. I can get a cheap lens for the iPhone on fleabay and glue the filters on.


Sent from my iPad using Tapatalk HD


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## mistergreen (Dec 9, 2006)

I just looked up on how these apps derived "lux" from the device's camera. It uses the digital ISO component of a camera like f stop, time, and luminance of the image to come up with a lux number. From my understanding that varies depending on the digital camera. Sorry, with is not a viable direction.


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## jeffkrol (Jun 5, 2013)

mistergreen said:


> I just looked up on how these apps derived "lux" from the device's camera. I uses the digital ISO component of a camera like f stop, time, and luminance of the image to come up with a lux number. From my understanding that varies depending on the digital camera. Sorry, with is not a viable direction.
> 
> 
> Sent from my iPad using Tapatalk HD


Well it may have some issues but CMOS sensors apparently have "value". 



> The traditional light detector with silicon diodes and a photometric correction filter is, with regards to the dynamic range, linearity and speed, still the ultimate sensor
> The BTS256 light sensor‘s CMOS diode array provides precise luminous spectrum measurement data. The spectral data is used for luminous value and scotopic illuminance calculations.


http://www.led-measurement.com/pdf-files/130926 FLYER_E_BTS256-LED.pdf
http://www.led-measurement.com/BTS256E-LED-Luxmeter/

AFAICT camera phones don't have "shutters" or variable apertures. (I could be wrong on this though.. )
It has to use the CMOS itself to determine it's "exposure".. 
Half the sensor is green filtered and is the primary luminance channel.. IF that can be used by an app (don't see why not) an accurate light level can be read off it..

Some interesting speculation though.. 
Nee more info..

Exposure is "standardized" and most camera "should adhere to it (they don't BTW, nor do all external exposure meters)


> If one puts in a very rough correction for these factors one ends up with a rather simple approximate formula for deriving lux falling on a diffusing white surface by pointing a camera at the surface:
> 
> Lux = 50 x fnumber/ (exposure time in seconds x ISO film speed)


http://www.conservationphysics.org/lightmtr/luxmtr1.php
Personally, at the cost of the LUX meters on the bay.. well kind of pointless.. but again an interesting thought puzzle..

Interesting read:
http://photo.stackexchange.com/questions/15182/how-well-do-smart-phone-light-meter-apps-work 





> Can they be used as incident-light meters without additional physical attachments like a diffuser dome?
> 
> No. You either need a diffuser dome like Luxi or an add-on incident meter like Lumu
> 
> ...


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## rexpongo (May 1, 2014)

I think those phone lux meters measure the brightness and give off a guesstimate. I have one for the iPhone, pretty sure the one on the right in the pic and under a 600w mh bulb it can tell the difference from 6" and 24", 18" has ~ 12500 lux from the bulb 6" has close to 50k lux


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## jeffkrol (Jun 5, 2013)

For fun..
https://www.maxmax.com/spectral_response.htm


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