How physical text layout affects reading from screen
The primary objective of this paper is to critically evaluate empirical research on some variables relating to the configuration of text on screen. The text layout variables are line length, columns, window size and interlinear spacing, with an emphasis on line length due to the larger number of studies related to this variable.
100 chars per line is faster for screen reading, maybe because we sit further away than from a book, so actual distance eyes need to sweep back is similar to 50-70 chars in a book.
Kindle/ipad therefore should maybe use same settings as a book? (50-70/line)
Many typographers would maintain that typographical variables cannot be considered individually. Designers should make decisions on each variable in relation to other variables. There is some support for this from studying the visual processes of reading. Long line lengths are said to need more interlinear spacing to ensure that the eyes locate the next line down accurately when executing a return sweep towards the end of a line. The angle of the return sweep should not be too small (Bouma 1980).
Most of the studies on line length report faster reading with longer lines, and point to the number of characters as the variable responsible for the differences, rather than physical line length (visual angle). Increasing characters per line, but maintaining a constant visual angle can result in faster reading
Going outside this range, with short or long lines, may affect reading speed, with slower reading of short lines and faster reading of lines as long as 100 characters
This pattern of results differs from those found with print, where Spencer (1968) states that line lengths should not exceed about 70 characters per line. Rayner and Pollatsek (1989) have interpreted the results from studies by Tinker and co-workers (summarised in Tinker 1963) and come to a more specific conclusion on line length. They deduce that Tinker’s work identified an optimal line length of 52 characters per line.
There appears to be no evidence to suggest that eye movements when reading from screen are different from reading print (Gould et al. 1987). However, we tend to sit further away from the screen than from printed matter when reading (Gould et al. 1987), so that a longer physical line length on screen subtends a smaller visual angle compared to the same physical line length in print.