>close after 3 minutes *continuous* sunshine

So if someone parks a car with the lights in your driveway and it stays
there for 3 minutes then the blinds close. Ok, maybe this makes sense.
Same for a thundercap making night out of day and opening the blinds just
in time to get dirt onto the windows from the first drops ;-)

The bolometers described by Britannica are metrology grade or whatever.
More everyday use bolometers are much more sensitive than the platinum
ones, because the innards are made of thermistor material. The reason a
bolometer will not be fooled by artifical sources (not easily) is the fact
that it measures the radiation intensity over a wide band of spectrum and
a wide solid angle (170 degrees is common). Since the sun is the strongest
source around by far (~1000W/m^2 on a sunny day at noon) it is easy to set
the trigger point such that only a Jupiter lamp at 5 meters will trigger
it falsely. Additionally it has a slow resonse so lightning and flashes
as well as cold light (streey lighting) will not impress it.

You could use a silicon detector instead if you would apply temperature
compensation and avoid its saturation in full light. Then the output
current would be proportional to incoming radiation flux and you could
have a set point wrt. this.

If I'd do this I'd use a 16C711 and an A/D or two and measure the peak
radiance over the last 7-8 days, median filter this, after making sure
that what I measured was indeed daylight (slow increase and decrease =
hefty low pass + median filter), and apply a trigger point expressed in
percent against this peak value. I'd also use a real time clock to
determine whether it's really day or night and have it override the light
trigger at certain times. The clock only needs to run in 10 minute ticks
and need not display realtime, so it counts binary in a register all by
itself. 24hrs = 1440 minutes = 144 10-minutes = 1(one) 8 bit PIC register.
;-)

Peter

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