The sunniest months are May and June. During these months sunshine duration averages between 5 and 6.5 hours per day over most of the country. The extreme southeast gets the most sunshine, averaging over 7 hours a day in early summer. December is the dullest month with an average daily sunshine ranging from about 1 hour in the north to almost 2 hours in the extreme southeast. Over the year as a whole most areas get an average of between 3 1/4 and 3 3/4 hours of sunshine each day.
The duration of bright sunshine is measured by a Campbell-Stokes sunshine recorder. This uses a glass sphere to focus the sun's rays to burn a trace on a curved piece of card behind it. The actual amounts of energy from the sun are measured by a more complex instrument called a solarimeter. Solar radiation measurements are used in agricultural applications and in solar energy projects.
Ireland normally gets between 1400 and 1700 hours of sunshine each year. The eastern Sahara Desert, however, which is the sunniest place in the world, gets an average of 4300 hours a year. Irish skies are completely covered by cloud well over half the time. This in turn is due to our geographical position off the northwest of Europe, close to the path of Atlantic low pressure systems which tend to keep us in humid, cloudy airflows for much of the time. 1887 was the sunniest summer in the 100 years from 1881 to 1980, according to measurements made at the Phoenix Park in Dublin. A more recent summer, 1980 was the dullest. The difference was considerable, with the summer of 1887 being twice as sunny as that of 1980.