What am I saying?? You don't need the formula for the sun's brightness at different altitudes.
You just need to tip the color-sample card, from the horizontal, toward the sun by an amount that's equal to the amount by which the summer-solstice deciination (23.44 degrees?) will be greater than the solar declination on the day of the experiment this week. That will give the color-sample card the same solar illumination that it will have at solstice noon. On Tue, Feb 28, 2017 at 5:09 PM, Steve Lelievre < steve.lelievre.can...@gmail.com> wrote: > John, thanks for the clarification, and your patience with my questions. > > All, I'm off to buy some photographic mattes to do experiements with. This > is all about having a horizontal dial face that is not too bright to view > even in the summer midday sun - so I'll go quiet now and report back after > the summer solstice. > > Steve > > > > On 2017-02-28 1:40 AM, John Lynes wrote: > > Hi Steve, > I'm sorry I've confused you. > > ... > > The take-home conclusion is that there is no single ideal reflectance for > the plate of a sundial. It varies with the sky illuminance. When Weber's > Law prevails, a reflectance of about 60 per cent is likely to be a safe bet. > > > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > >
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