As promised at the end of last month, an evaluation of the sensor values under differing light conditions.
| Time | 0hms | Cloud cover (8ths) | Description | Observer | |
| 12/06/11 | 04:45AM | 3300 | 1 | pre sunrise Clouds on eastern horizon, lit by sunlight – sun behind hills | chrisw |
| 05:00AM | 2000 | 1 | Sunrise – sun just behind trees | chrisw | |
| 05:07AM | 1750 | 1 | Sunrise – cirrus band and blue sky overhead | chrisw | |
| 05:10AM | 2000 | 1 | Same conditions but in shadow area to get down scatter reading | chrisw | |
| 05:15AM | 1050 | 1 | blue sky cirrus clouds overhead sun about 3 degrees above horizon | emily | |
| 05:30AM | 800 | 1 | same conditions but sun about 1-2 degrees higher | emily | |
| 05:45AM | 700 | 2 | cirrus clouds and blue sky sun at 5 degrees bank of cloud coming in from south not yet affecting readings | emily | |
| 06:00AM | 450 | 3 | cirrus cloud still above sun at about 7 degrees bank of cloud from south moving further north | emily | |
| 06:15AM | 375 | 5 | cirrus cloud and blue sky still above sun at about 10 degrees bank of cloud from south almost over head though | emily | |
| 06:25AM | 435 | 7 | sun slightly covered by thin bank of cirrus cloud and cloud from south over head now beginning to affect readings | emily | |
| 06:40AM | 700 | 8 | only last snipits of blue sky sun covered by clouds from south (now covering most of the sky), sun at 13 degrees | emily | |
| 06:55AM | 635 | 8 | sun covered by thick cloud at about 17 degrees | emily | |
| 07:15AM | 800 | 8 | sun now not visible behind cloud | emily | |
| 07:50AM | 700 | 8 | sun now not visible behind cloud raining at the moment (light to medium rain) | emily | |
| 08:30AM | 700 | 8 | still raining and still no visible sun | emily | |
| 09:00AM | 650 | 8 | clouds slightly lighter white still raining and wind picking up | emily | |
| 09:30AM | 700 | 8 | full sky of thick cloud no visible sun, medium rain and wind picking up | emily | |
| 10:00AM | 550 | 8 | full sky of thick cloud still no visible sun wind dying down rain picking up | emily | |
| 10:30AM | 430 | 8 | cloud directly above head whitening slightly, rain still getting heavier. | emily | |
| 11:00AM | 500 | 8 | cloud not any whiter, rain dying down | emily | |
| 11:30AM | 480 | 8 | cloud not any whiter, rain the same | emily | |
| 12:00PM | 550 | 8 | Same conditions as before | emily | |
| 12:30PM | 530 | 8 | Same cloud yet raining heavily | emily | |
| 01:45PM | 545 | 8 | clouds slightly lighter white still raining | emily | |
| 02:30PM | 590 | 8 | Same cloud yet raining getting lighter | emily | |
| 03:00PM | 530 | 8 | raining heavily clouds still full covering sky | emily | |
| 04:00PM | 680 | 8 | Overcast | chrisw | |
| 06:00PM | 650 | 8 | still overcast | emily | |
| 07:00PM | 750 | 8 | still overcast | emily | |
| 07:30PM | 670 | 8 | still overcast but clouds lightening in colour | emily | |
| 08:00PM | 900 | 8 | odd snipits of blue sky overhead but low cloud/ fog coming in from south | emily | |
| 08:40PM | 1600 | 8 | blue sky gone low cloud from south still moving in | emily | |
| 08:55PM | 3330 | 8 | dark low lying clouds, drizzle | emily | |
| 09:05PM | 3700 | 8 | Still dark low lying clouds, drizzle | emily | |
| 09:15PM | 3800 | 8 | same as above | emily | |
| 09:20PM | 6500 | 8 | same as above | emily | |
| 09:29PM | 7400 | 8 | Supposed sun set however unknown because sun covered by thick cloud, still drizzle | emily | |
| 09:35PM | 10000 | 8 | beginning to darken slightly. | emily | |
| 09:50PM | 25500 | 8 | slightly darker but still drizzling | emily | |
| 10:00PM | 72000 | 8 | getting darker almost black sky yet still able to see drizzle stopped | emily | |
| 10:08PM | 160000 | 8 | dusk | chrisw | |
| 10:20PM | 600000 | 8 | dusk | chrisw | |
| 10:35PM | 2350000 | 8 | dark | emily | |
| 13/06/11 | 10:20AM | 240 | 5 | broken cloud – in sunshine | chrisw |
| 11:00AM | 290 | 6 | sun behind thin white cloud | chrisw | |
| 12:40PM | 250 | 4 | broken white cloud – sun unobstructed | chrisw | |
| 07:05PM | 298 | 3 | cirrus partially obscuring sun | chrisw | |
| 09:55PM | 12400 | 2 | 10 mins after sunset | chrisw | |
| 14/06/11 | 01:00AM | 24000000 | 2 | moonlight ¾ moon | chrisw |
So, in conclusion the simple photo-resistor (LDR) sensors chosen give a range of values ranging from a few hundred Ohms in bright sunlight, to over 20M Ohms under moonlight.
This is obviously too wide a range of values to cover with a single scale (there are only 1023 steps on the ADC input on the micro-controller board I will be using) – so tests and some graphing will follow to chose what ranges to cover
I have located a conversion table for EV (exposure value) to Lux for our photographic light meter, so will retest some of the above typical values in conjunction with the Lux reading to give some more measurable values to the table
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