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Light intensity measurement using your camera

#1 User is offline   sthh 

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Posted 14 February 2014 - 09:41 AM

This is a good tool to measure the amount of light that a certain area has, on it's most sunny time.
It will allow us accurately select the type of orchids and place them in suitable location.

Example:
Low light orchids such as Phalaenopsis needs 1000 to 1500 footcandles
Medium light orchids such as Cattleyas needs 1500 to 3000 footcandles
High light orchids such as Vandas needs 3000 to 4500 footcandles

You need a camera, and a white cardboard, and you need to measure the light during the sunniest period in the location.
1. Place the white cardboard in the location.
2. Set your camera to AUTO mode, let the camera choose all the setting, aim at the white cardboard and shoot.
3. Look at the photo exif details. (You can just save the photo, and right click on the jpeg, select "Details")

The formula to work out foot candles from a camera is:
6*F^2/(I*E)

where F = F stop (aperture)
I = ISO setting
E = Shutter Speed (exposure)

Here's an example.

My vanda is getting about 6 * 11 * 11 / (200 * 1/800) or 2904 footcandles in the morning.
http://i498.photobucket.com/albums/rr346/trelch/Untitled_zpsf8815e42.jpg

This post has been edited by sthh: 14 February 2014 - 05:50 PM

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#2 User is offline   Chatbud 

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Posted 14 February 2014 - 10:29 AM

I got one iPhone app that measures light intensity. Dun know zhun or not
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#3 User is offline   sthh 

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Posted 14 February 2014 - 11:12 AM

View PostChatbud, on 14 February 2014 - 10:29 AM, said:

I got one iPhone app that measures light intensity. Dun know zhun or not


Don't know if your iPhone app is accurate. You can try doing the camera measurement, and then your iPhone app measurement, and see what's the difference in reading.
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#4 User is offline   brett 

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Posted 14 February 2014 - 11:41 AM

Interesting, will try ... but what is the 2 in the formula as your example has no 2. And what does ^ on the formula mean ? Sorry, am no math guy :unsure:/>/>

I used two Iphone apps, on a small setup, with phone just above the plant, they are close to matching my grow light's claim of around 3000++ lux (for one). On the bigger setup, they vary more, I get around 25000 lux on 1 app and 17000 lux on another app. Anyway, either result means I am getting enough light I guess.

Will try this too and compare with your formula (once I understand it)

https://www.youtube....h?v=_xU0pWjugTo

This post has been edited by brett: 14 February 2014 - 11:53 AM

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#5 User is offline   sthh 

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Posted 14 February 2014 - 12:50 PM

6*F^2/(I*E)

The F^2 is F square or F * F

Btw, 1 footcandle is about 10.764 lux

This post has been edited by sthh: 14 February 2014 - 01:07 PM

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#6 User is offline   spheredome 

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Posted 14 February 2014 - 04:40 PM

Interesting.

Is it divide or multiple after the F power of 2?

6*F^2/(I*E)

6 * 11 * 11 * (200 * 1/800)

View Poststhh, on 14 February 2014 - 09:41 AM, said:

This is a good tool to measure the amount of light that a certain area has, on it's most sunny time.
It will allow us accurately select the type of orchids and place them in suitable location.

Example:
Low light orchids such as Phalaenopsis needs 1000 to 1500 footcandles
Medium light orchids such as Cattleyas needs 1500 to 3000 footcandles
High light orchids such as Vandas needs 3000 to 4500 footcandles

You need a camera, and a white cardboard, and you need to measure the light during the sunniest period in the location.
1. Place the white cardboard in the location.
2. Set your camera to AUTO mode, let the camera choose all the setting, aim at the white cardboard and shoot.
3. Look at the photo exif details. (You can just save the photo, and right click on the jpeg, select "Details")

The formula to work out foot candles from a camera is:
6*F^2/(I*E)

where F = F stop (aperture)
I = ISO setting
E = Shutter Speed (exposure)

Here's an example.

My vanda is getting about 6 * 11 * 11 * (200 * 1/800) or 2904 footcandles in the morning.

This post has been edited by spheredome: 14 February 2014 - 04:41 PM

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#7 User is offline   sthh 

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Posted 14 February 2014 - 05:49 PM

View Postspheredome, on 14 February 2014 - 04:40 PM, said:

Interesting.

Is it divide or multiple after the F power of 2?

6*F^2/(I*E)

6 * 11 * 11 * (200 * 1/800)


Divide. Sorry, my mistake in the example. But the formula is correct, and the result is correct too, lol

This post has been edited by sthh: 14 February 2014 - 05:50 PM

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#8 User is offline   Cindy 

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Posted 14 February 2014 - 06:03 PM

I remember that a friend sent me a EXCEL file with the formula so that I could plonk in the variables and get the lux right away. After a few tries, I went to buy a lux meter. It is very useful for checking the light intensity under my T5s.
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#9 User is offline   digitalgate 

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Posted 14 February 2014 - 08:30 PM

Just in case guys dont know. The palm method does a fairly good job . No need formula and pay for it. But it need someone one to show u
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#10 User is offline   Lionel Teng 

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Posted 14 February 2014 - 09:28 PM

don't worry much about the lux measurement to be exact is use to measure space light level of a conservatories like how the GBB works letting much light in without letting in much heat.

PALM METHOD Yes it works very accurately.

For orchidists an exact measurement will always be letting the leafs receive much light and see how the leafs reacts. A jade green lustre will always be safe than a yellow green sheen on the leafs !. If you see yellowish green leafs kindly change to another spot and let the plant to be familiarize the environment such as anggrek bulan which usally grows in dense canopy of a emergent trees or the mangroves.

If the leafs is wrinkled that means the area is dry and warm which cause the leafs to dessicate.

Lastly there no hard and fast rule is up to a individual on how to deal with the light level on a specific spot before the plants are bought or grow and settle in a spot.
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#11 User is offline   brett 

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Posted 14 February 2014 - 11:30 PM

Well, after reading about the camera way, and seeing others having recommending a fixed aperture, others the metering type (average, spot), and another saying distance is an important factor (which I believe in), I too thought it best to just get a lux meter, $15 on ebay. I don't have a single orchid plant, so I'll use it for other stuff.

What is the palm method ? All I can find is a hand method ... => http://www.greencult...-gardeners.html


View PostCindy, on 14 February 2014 - 06:03 PM, said:

I remember that a friend sent me a EXCEL file with the formula so that I could plonk in the variables and get the lux right away. After a few tries, I went to buy a lux meter. It is very useful for checking the light intensity under my T5s.

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#12 User is offline   keff 

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Posted 15 February 2014 - 12:28 AM

What about those free lux meter apps you can download for Iphone or Android? Anyone compared the results with a purpose built lux metre to see if they are accurate?

This post has been edited by keff: 15 February 2014 - 12:29 AM

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#13 User is offline   digitalgate 

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Posted 15 February 2014 - 07:42 AM

I let u guys know . Dont have time recently..
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#14 User is offline   brett 

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Posted 15 February 2014 - 11:48 AM

View Postkeff, on 15 February 2014 - 12:28 AM, said:

What about those free lux meter apps you can download for Iphone or Android? Anyone compared the results with a purpose built lux metre to see if they are accurate?


I tried three free ones, they are only similar in results in low light. With bright light, they have widely different results. Even Megaman, the maker of some of my grow lights, has a free app, with calibration options.

Anyway, if I did not use a lot of CFL grow lights, which are known to lose intensity as they grow older, I don't think I need a lux meter. In the meantime, while I haven't found the right LED yet to replace the CFLs, I'll use a cheap lux meter to monitor them. It looks like a camera external light meter, with the white ball which has a sensor to measure incident light (light falling on the subject).
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#15 User is offline   drektster 

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Posted 19 February 2014 - 07:43 PM

View Poststhh, on 14 February 2014 - 09:41 AM, said:

This is a good tool to measure the amount of light that a certain area has, on it's most sunny time.
It will allow us accurately select the type of orchids and place them in suitable location.

Example:
Low light orchids such as Phalaenopsis needs 1000 to 1500 footcandles
Medium light orchids such as Cattleyas needs 1500 to 3000 footcandles
High light orchids such as Vandas needs 3000 to 4500 footcandles

You need a camera, and a white cardboard, and you need to measure the light during the sunniest period in the location.
1. Place the white cardboard in the location.
2. Set your camera to AUTO mode, let the camera choose all the setting, aim at the white cardboard and shoot.
3. Look at the photo exif details. (You can just save the photo, and right click on the jpeg, select "Details")

The formula to work out foot candles from a camera is:
6*F^2/(I*E)

where F = F stop (aperture)
I = ISO setting
E = Shutter Speed (exposure)

Here's an example.

My vanda is getting about 6 * 11 * 11 / (200 * 1/800) or 2904 footcandles in the morning.
http://i498.photobucket.com/albums/rr346/trelch/Untitled_zpsf8815e42.jpg


thou the shutter speed depends on the aperture. so a low aperture can achieve faster shutter speed.
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#16 User is offline   sthh 

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Posted 19 February 2014 - 09:40 PM

View Postdrektster, on 19 February 2014 - 07:43 PM, said:

thou the shutter speed depends on the aperture. so a low aperture can achieve faster shutter speed.


Yup. On a bright sunny day, if you let your aperture goes wide open, and have a low F-stop, the shutter speed will be much faster.
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