Year	Hours
1970-01-01	1845
1971-01-01	1812
1972-01-01	1813
1973-01-01	1789
1974-01-01	1736
1975-01-01	1685
1976-01-01	1672
1977-01-01	1665
1978-01-01	1634
1979-01-01	1612
1980-01-01	1602
1981-01-01	1601
1982-01-01	1586
1983-01-01	1571
1984-01-01	1563
1985-01-01	1546
1986-01-01	1531
1987-01-01	1510
1988-01-01	1506
1989-01-01	1501
1990-01-01	1496
1991-01-01	1486
1992-01-01	1493
1993-01-01	1482
1994-01-01	1490
1995-01-01	1501
1996-01-01	1506
1997-01-01	1496
1998-01-01	1485
1999-01-01	1482
2000-01-01	1480
2001-01-01	1461
2002-01-01	1435
2003-01-01	1429
2004-01-01	1417
2005-01-01	1417
2006-01-01	1414
2007-01-01	1412
2008-01-01	1415
2009-01-01	1396
2010-01-01	1425
2011-01-01	1436