On Sunday, 22 April 2018 19:32:02 UTC+1, Nick Gardner wrote:
On 22/04/2018 18:30, Keith Harris wrote: I've come to the conclusion
you can't compare the two systems like for like. However, I do feel the
BL is more accurate,
Hmmmm, at the moment I am far from convinced that the BL recorder is
'more' accurate. I find it hard to believe that when the sun is shining
brightly and you can feel its heat, with its disk clearly visible and
there is a distinct, sharp edged shadow on the ground - that the sun is
NOT shining. The BL recorder can say that.

Also, and Ole agrees with me that the BL recorder can be fooled by
indirect light, i.e., lots of small cumulus clouds giving plenty of
reflected light can raise (as it does with my solar irradiation and UV
measurements) the level somewhat above the threshold and record sunlight
even though the sun itself is partly obscured and not casting a shadow.
I have noticed this on occasions and I contacted Ole to report it.

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.

--
Nick Gardner
Otter Valley, Devon
20 m amsl
http://www.ottervalleyweather.me.uk

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)