Measuring light levels with an SLR camera

[jerrymeola]

A real rough guideline for orchids flowering level light levels are:
Vandas 6-8000 foot candles
cattleyas 3500-4000
dendrobiums 2000-4000 most common dens are the same as cattleyas but many species can vary
Oncidium alliance (basically all thin leaf types) 2000-2500
Phalaenopsis 1000-1500
Paphs (Lady Slippers) 1000 (African Violet light and conditions for those who raise african violets)

Most orchids will grow and live in much lower levels but the light is the most important condition for flowering. Note that once the flower buds sets, it is not necessary to keep it in that light level, and can be moved indoors for enjoyment of the flowers

To measure light using a SLR camera either film or digital set the ASA or ISO to 100 place a piece of clear white paper in the area you want to measure and fill the picture frame witht he paper, it is not necessary to focus. Take a light reading
speed fstop
1000 foot candles 1/2000 f2.8
1/1000 f4
1/500 f5.6
1/250 f8
1/125 f11
2000 foot candles 1/2000 f4
1/1000 f5.6
1/500 f8
1/250 f11
1/125 f16
4000 foot candles 1/2000 f5.6
1/1000 f8
1/500 f11
1/250 f16
1/125 f22
8000 foot candles 1/2000 f8
1/1000 f11
1/500 f16
1/250 f22

If you have a digital camera that does not set lower than 200 ISO use it and double the foot candles
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[butt0n]

I just took a light reading and I got:
1/1250 f4.5
1/250 f4.0
Both were taken at the same window, but the latter was farther away from the window. What does this translate into?

[jerrymeola]

It shows you how light quickly falls off with distance from a window. The second reading is less than half the light of the first one.

It is about 1600 foot candles at the first reading and about 600 at the second.

It makes me think I need to expand the chart for non-photographers.

[butt0n]

Thanks Jerry. Is there a way to calculate that on our own? I'd hate to keep asking. I hope to get some grow lights soon to up the footcandles since I have a lot of catts.

[Anton]

Still simpler is to get a dedicated fc/lux meter, see my post under Photograpahy 101, no calcs needed point and read, couldn't be easier.

Jerry's done a great job with the conversion table, but to me if you want to be serious about your light measuring, then YOU HAVE TO GET a dedicated meter that is designed for just this purpose.

[Sharyn]

Originally Posted by Anton

Still simpler is to get a dedicated fc/lux meter, see my post under Photograpahy 101, no calcs needed point and read, couldn't be easier.

Anton, I agree. This camera measuring stuff is for the birds. I purchased a cheap $29 meter and it's as useless as a screen door on a submarine, therefore, I'll be saving up for a decent light meter. It's amazing how much difference in light just inches away from the window.

[jerrymeola]

The reason I made this post is the cost of a light meter these days.

Before automatic cameras you could buy a decent meter for $20 and a professional meter for $60. Last time I tried to buy a high quality meter it was about $300.

If anyone finds something they like for a more reasonable price, please let us know.

[Sharyn]

Jerry: I think your chart for measuring the fc is very helpful and I wish I could that. My problem is, I don't have an SLR and trying to measure with my cheap digital is too confusing as the lowest OSI is 80 and I don't know how to measure correctly for the f-stops.

[jerrymeola]

Since digital photographs are free and can be deleted, if you have camera software that records the speed and shutter of a photo that was taken, then shoot a photo of the piece of paper (with a little description of where and when) and view the photo data. Then you have a permanent record of the light level.

Light level are exponential. That is for every change the numbers double or are halved. Sharyn your camera setting of 80 is almost the same as 100. The first meaningful difference is 50 or 200.

If you look at the chart speed doubles with each change. Less than double is not very meaningful.

Mostly Orchids are not that critical. Most orchids can live ever more than their recommended range. The numbers that are in the middle of the charts are not that different.

Take the whole chart as a loose guide.