isophotaladj.

1904 D. Burnett in Trans. Amer. Inst. Electr. Engineers 20 74 The impression they convey would much more nearly accord with what actually occurs if the curves showed not the intensity of light in the various directions, but the lines along which the lighting is equal at any point. Such curves may be called ‘isophotals’, and while they are of the same general shape as intensity curves, their dimensions are as the square root of the radii.

1904 D. Burnett in Trans. Amer. Inst. Electr. Engineers 20 74 The tendency of enclosing an arc.., either in the interior gas globe or more particularly in the outer diffusing globe, is to make such an isophotal curve approach more nearly a circle.

1930 Astrophysical Jrnl. 71 365 The total luminosity of the entire nebula out to the distance r/a is found by integrating successive elliptical rings on the assumption that the isophotal contours are all similar ellipses.

1964 Jrnl. Geophysical Res. 69 487/1 These regions were characterized by systems of isophotal contour lines, sometimes occupying virtually the whole observed area.

1964 Jrnl. Geophysical Res. 69 487/2 Isophotal sky maps.

1964 A. Cox Syst. Optical Design ix. 367 The contour lines are ‘isophotals’ mapping areas of equal intensity.