On 25/04/2018 08:36, wrote:
On Wednesday, April 25, 2018 at 6:39:48 AM UTC+12, Keith Harris
wrote:
On Sunday, 22 April 2018 19:32:02 UTC+1, Nick Gardner wrote:

The Met Office might take some convincing as to the 'accuracy' of
the BL as I believe the KZ recorder uses the same method as the
R&D, i.e., the difference between sunlight and shadow.

I prefer to keep it simple, if there's a sharp-edged, distinct
shadow then then the sun is shining.

I think that is a reasonable definition - otherwise thin cirrus haze
with the sun barely visible could be counted as sunshine. It is often
not far short of a similar brightness with ~90% transmission.

Cloudy bright in the old photographic rule of thumb era.

I've not noticed the indirect sunlight recording, however, today my
R&D recorded 0.02 hours, whereas the BL 2.00 hours, it did brighten
up, but I don't remember much blue sky. It's a shame I wasn't at
home as I would like to have monitored what was going on.

Keith (Southend)

My issue with any single fixed threshold is that it doesn't allow for
seasonality - in higher latitudes at least, I don't regard winter's
bright sunshine as being equivalent to summer's bright sunshine. But

That is more a flux per unit area on the ground.

Once the sun's altitude is more than about 15 degrees the extinction is
less than a magnitude. IOW 40% of the suns light reaches the ground. But
it is spread more thinly and for a shorter time in mid winter. See

http://www.orion-drustvo.si/MBKTeam/...extinction.htm

Interestingly with solar panels in mid winter the much cooler conditions
partly compensate for the low sun by improving PE efficiency.

I agree with the notion that when compared with rainfall and
temperature measurement, sunhisne measurement will always be more
subjective.

I always wanted one of the charred paper crystal ball sun recorders.

--
Regards,
Martin Brown