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
__________________

[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.

[Joey1987]

Hi guys. I tried to do a light reading, but I cannot select shutter speed on my camera. However, when I open the image on my computer, the program gives me info pertaining to f-stop and exposure. I took a light reading in three different locations, with the following values:

1/283 f/2.8
1/283 f/2.8
1/1401 f/5.5

I am thinking the first two readings are way too low for growing a phal successfully. However, the rooms did not look this dark to the naked eye. Also, although two of the rooms have the same readings, one of them is situated on the opposite side of the house, therefor facing NNE (only guessing). The f/5.5 reading was taken where I am sure the plant would get sunburnt. I have no idea where to put the plants now! Is it possible that there is no place in my house with sufficient lighting for my phals?

My mom had some African Violets a while back and they were flowering. I am thinking I should put the phals in this spot?

Also, since I can only select ISO on my camera, how sure can I be that these readings are accurate? I selected ISO 100.

I am currently keeping my orchids in the SSE location with light reading 1/283 f/2.8 and have not yet seen any difference in the plants' conditions. I must add that I have only had them for three weeks.

[Ray]

You can see how the f-stop affects the readings by this calculator: Click Here

[Emma Grey]

That is so cool! I will have to use my camera to take a light reading near my Phal.

[jerrymeola]

It was fun to see this old post show up again.

Since then Chinese lux meters have gotten on the market for about $30 so they are reasonable. Their readings may be off by 10% or so as mine was. Since a lux is slightly less than 11 to the foot candle the error made the meter read at 10 times so conversion was an easy divide by ten.

For those that own an ipod there is an app that will convert it into a light meter.

[NiNiDazzle]

Originally Posted by jerrymeola

It was fun to see this old post show up again.

Since then Chinese lux meters have gotten on the market for about $30 so they are reasonable. Their readings may be off by 10% or so as mine was. Since a lux is slightly less than 11 to the foot candle the error made the meter read at 10 times so conversion was an easy divide by ten.

For those that own an ipod there is an app that will convert it into a light meter.

I would have never thought to look for a light meter for my iPhone. I just downloaded the free app and will test it out tomorrow when the sun is out.

[BluPeaches]

Nini, did you ever try this? How did it work out?

[NiNiDazzle]

Originally Posted by BluPeaches

Nini, did you ever try this? How did it work out?

I did try out the app and with the link that Ray provided, it gave a very rough estimate. I'm just a tad anal so that wasn't good enough for me. I ended up buying a light meter for ~$40.

I grow indoors under light so I need more exact FC depending on where and how far from the light bulb. If you are growing outside or at a windowsill, this app should be more than sufficient.

[BluPeaches]

Thanks.

[wu78754]

The Chinese lux meters are driving some businesses extinct. A few years ago I bought a Sekonic candle foot meter that cost me around $300. Today you can buy a Chinese lux meter that's 10 times as sensitive for about $10.

Originally Posted by jerrymeola

It was fun to see this old post show up again.

Since then Chinese lux meters have gotten on the market for about $30 so they are reasonable. Their readings may be off by 10% or so as mine was. Since a lux is slightly less than 11 to the foot candle the error made the meter read at 10 times so conversion was an easy divide by ten.

For those that own an ipod there is an app that will convert it into a light meter.

[jpyerry]

A couple of months ago, I purchased an Extech LT300 light meter on ebay that came with a NIST certificate of calibration, the meter has accuracy of +/- 5% which I think is accurate enough for our purposes and measures in lux and footcandles. It was very lightly used, if the packaging were intact, I would have thought it was brand new, it even still had the plastic protector over the viewing screen. Retail on these meters is about $150 and the NIST calibration can easily add $100 or more to the cost. I got it for about $100.

So, with patience high quality meters can be found, you just have to look around and be patient.

Justin