Applying the Hooper's first-order theory, we have calculated the static micro-electric field distributions and have examined the validity of the first-order theoretical calculations. The Lyman line profiles (n→1) from hydrogenic ions have been calculated. As the principle quantum number n is odd, there is no central peak and two splitted peaks exhibit for the Lyman line profile. Electron-impact broadening has negligible effects on such sepera-rions of the splitted peaks, which are suitable for plasma density diagnostics. The Lyman line proifles in the wing regions, which are formed dominantly by the static micro-electric field distributions, can also be applied for plasma density diagnostics.