On Monday, 23 April 2018 11:22:20 UTC+1, John Dann wrote:
On 23/04/2018 10:24, Nick Gardner wrote:

The BL uses a simple solar irradiation measurement coupled with a
quite clever software code to determine a sunshine/no sunshine
output.


Are you sure that's how BL works? I thought that the later design tries
to emulate the 120W/sqm direct irradiance measurement via some simple
but well thought-out optics. BICBW

I think the 'clever software' you're referring to is just the
traditional way used by a number of different software packages to try
and estimate sunshine hours from global irradiance by setting some
arbitrary threshold above which measured irradiance as a % of maximum
theoretical radiance is classified as bright sunshine. It's a little
intricate calculating the theoretical max for time and day of year,
lat/long, timezone etc and not forgetting the equation of time but it's
basically just coding some well-defined trig. IIRC the only real gotcha
is remembering to allow for which quadrant the ATAN result ends up in.

http://www.sunrecorder.net/googlemap...serial=1010 9

I think you are correct John in what you say, as I quoted earlier in the thread. It was interesting to see that this morning, cooler and clearer, not as hazy, that my BL started recording about 15 minutes after mathematical sunrise, so it gave me some confidence that the Threshold(s), that run on a sliding ruler, are ok. The last few days have probably been hazier than I thought. So it is true what Ole said, and the algarithm seems correct based on the WMO definition of 120W/m2, which is very old and also to a great extent on the Cambell-Stoke performance.

Again, you can't really compare systems like for like, but the do what they say on the tin. Althoug I get some quite large day to day variabilities between the BL and the InstroMet systems, I tend to find the monthly totals are never that far apart.

Keith (Southend)