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LIGHT MEASUREMENT USING A CAMERA |
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LIGHT MEASUREMENT USING A CAMERA |
Many orchid books mention 'foot candles' when discussing the light requirements required for orchids. Sophisticated instruments can be obtained to measure the light received in a glasshouse or other area, but this equipment is usually beyond the resources of most orchid growers. As an alternative you can obtain a reasonable estimate of foot candles by using a camera equipped with a light meter. There is some disagreement regarding the accuracy of such measurements, but I believe a useful indication of the light levels can be obtained, accurate enough for most practical purposes.
The procedure is as follows:-
Set the film speed on the camera to 100 ASA or Din.
Put a sheet of white paper on the place where you want to perform the measurement so that the paper receives the highest light intensity.
Point the camera at the paper and ensure that the image of the paper fills all the view finder so you obtain a correct reading of the reflected light. You do not need to focus your camera.
Read the values that the light meter in you camera gives, and translate the light meter readings to light intensity in foot candles from the following table.
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INDICATIVE LIGHT INTENSITY IN FOOT CANDLES |
Aperture settings | ||||||||
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f 1.4 | f 2 | f 2.8 | f 4 | f 5.6 | f 8 | f 11 | f 16 | f 22 |
| 1/4 sec camera speed |
0.5 |
1 |
2 |
4 |
8 |
16 |
32 |
64 |
125 |
| 1/8 |
1 |
2 |
4 |
8 |
16 |
32 |
64 |
125 |
250 |
| 1/15 |
2 |
4 |
8 |
16 |
32 |
64 |
125 |
250 |
500 |
| 1/30 |
4 |
8 |
16 |
32 |
64 |
125 |
250 |
500 |
1000 |
| 1/60 |
8 |
16 |
32 |
64 |
125 |
250 |
500 |
1000 |
2000 |
| 1/125 |
16 |
32 |
64 |
125 |
250 |
500 |
1000 |
2000 |
4000 |
| 1/250 |
32 |
64 |
125 |
250 |
500 |
1000 |
2000 |
4000 |
8000 |
| 1/500 |
64 |
125 |
250 |
500 |
1000 |
2000 |
4000 |
8000 |
16000 |
| 1/1000 |
125 |
250 |
500 |
1000 |
2000 |
4000 |
8000 |
16000 |
32000 |
| 1/2000 |
250 |
500 |
1000 |
2000 |
4000 |
8000 |
16000 |
32000 |
64000 |
EXAMPLE
If you set an exposure time of 1/125 second and the aperture f.stop is f 11, from the table the light intensity is approximately 1000 foot candles.
This material was originally produced by the Swedish camera manufacturer Hasselblaad.
For foot candles to lux conversion (and vice versa)
together with temperature conversion tables click here
This is part of a larger site maintained by Phil,
click the graphic below for site Index Page
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Specific page counter added 21.7.99
Site established 9th May 1998
This page initially uploaded 21 July 1999
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21 July 1999