A comparison is made between the results of a number of programs currently in use for computing theoretical X-ray binary optical light curves. For four programs excellent agreement is found, and the small differences between them are the result of different treatments of limb darkening. The use of approximate limb-darkening laws is discussed and it is shown that the commonly used linear approximation generally tends to overestimate the ‘larger’ light amplitude. A discrepancy between the results obtained by Hutchings and other investigators is pointed out.