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Growing under Lights

digital camera as a light meter

19 years ago

i own a fuji finepix A210 point and shoot digital camera. i've read here that it may be used as a simple light meter. can someone explain this to this camera newb?

tia, rick

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Comments (4)

shrubs_n_bulbs
19 years ago
I'm here and I know how to do this :) Results will be approximate of course, but close enough for our needs as plant growers.

You need a piece of white paper or card. You need to set your camera to point-metering mode so that it is only measuring the light at the centre of the view. You also need to use a shooting mode that shows you the ISO speed, F-stop and exposure, or allows you to fix some settings and shows you the rest.

So, put the paper/card at the spot to be measured and point your camera at it with the metering spot on the card. You will probably need to press the button down halfway to get the camera to measure. Read off the ISO speed (I), the F-stop (F), and the exposure in seconds (E). Focus doesn't matter. Telephoto, zoom, or macro modes don't make any difference, but may reduce the availabe settings the camera can pick. Just make sure the metering spot is completely filled with the white card. The light intensity in foot-candles is given by:

6*F^2/(I*E)

As an example, if the speed is ISO 50, the F-stop F/2.8, and the exposure 1/500 sec, then the intensity in foot-candles is:

6 * 2.8 * 2.8 / (50 * 1/500) = 470 foot-candles

Try it and feel free to come back with any questions or comments.
aspen31
Original Author
19 years ago
great, thanks for the explanation. i am a planted aquaria guy, and i want some idea of how bright my lights are with different lamps and reflectors, and esp some idea of how much they will have dimmed over time, by recording this data and checking later.

time to get the manual out for my camera. it hasn't come out of automatic mode yet.

rick
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Thank you both for your responses. I will see if any of those are required at the moment, after I downloaded a few light meter android applications. For the time being I will compromise without the PAR. My android - samsung Galaxy S Advance - an old model was not reporting seemingly correction lux of foot-candles numbers, so therefore I downloaded that applications in my wife's cell phone - a newer model - Samsung Galaxy Note 2 and it seems the numbers look fine as when I take it direct sunlight it shows me 11,900 foot-candles and as I bring it in the shade, they reduce and inside the house they reduce further - coming upto 10 foot candles. I also tried it by keeping on my window and as the sun rose the reading gradually went up from early morning sunrise - 100 fc onward to 2000 fc. No direct sun on my window. The only further thing would be for me to have a comparison with an actual meter. Perhaps one of you could download these 2 android applications and compare its result with the actual meter readings. Here are the links 1/ This one gives both lux and fc readings and has a max reading of around 12000 fc and 129000 lux https://play.google.com/store/apps/details?id=com.bti.lightMeter&hl=en On your android phone you can search by "Light Meter Borce Trajkovski" 2/ This one has a nice display but only lux reading and only a max of 102000 lux. https://play.google.com/store/apps/details?id=spaceware.lightmeter&hl=en On your android phone you can search by " Light-O-Meter Spaceware" Both have ok to good reviews - especially the first one where comparision with an actual meter have been reported by reviewers to be varying by approx. +/- 5% Thanks again for the input. Saood
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gonzyro
18 years ago
Hello!! IÂ´m sorry IÂ´m like intervining here, but IÂ´d also like to use my camera as a light meter. I have an Olympus C-770, and I still need to read a lot to find all the parameters you mention. But in the meantime, I have a question. What does the value you get after you solve the equation means? What IÂ´m trying to ask is what is (in your example) 470 foot-candles? How is this measure related to the light needed for a shade plant, for example? Can you give me this information or at least tell me where can I find it? thank you very much!
shrubs_n_bulbs
18 years ago
A few web sources will indicate foot-candle values for different plants, but here is a rough guide.

Direct sunlight: 10,000fc, maybe a little more
High light plants: 1,500fc-5,000fc
Open shade: 1,000fc
Medium light plants: 500fc-1,000fc
South-facing window (not direct sunlight): 500fc
Low light plants: 100fc-500fc
North-facing window: 100fc
Domestic indoor lighting: 10fc

These numbers are all approximate, but should give you an idea of roughly where you are. So 470fc would be a very dull day outdoors or a bright indoor position near a south window, and suitable for many plants but not high-light plants.

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