A photoelectric spectrum scanner has been built in Edinburgh University Department of Astronomy by Dr. M.J. Smyth and the author. A feature of the spectrum scanner is the use of a small fraction of the undispersed starlight to provide a reference beam for compensating changes in atmospheric transparency, seeing and guiding errors. Using the ratiometric spectrum scanner Nova Cygni 1975 has been observed (Kontizas, Kontizas & Smyth 1976). Photoelectric spectra of 72 early type stars have been studied for two purposes: a) to investigate the luminosity effect; and b) to establish a temperature scale for stars from BO to early A spectral type. The ultraviolet part of the spectra has been observed with a 27-cm ultraviolet telescope which gave low dispersion spectra over the wavelength range 1350 A - 2550 A and a broad band measurement centred at 2740 A. This telescope was installed in the TD-1A satellite (Boksenberg et al. 1973). The visible part of the spectra has been observed by E. Kontizas using the spectrum scanner mentioned earlier or by K. Nandy using a single channel, low resolution, spectrum scanner. Real spectra have been compared with synthetic spectra from the models of Kurucz, Peytremann & Avrett (1974) for the estimation of Teff. The used data cover a wide wavelength range (5556 A - 1350 A) and the models include a very large number of lines (1,760,000 lines) in order to compute a statistical representation of the line opacity in terms of distribution functions. It has been found that for early B stars the supergiants are cooler than the main sequence stars of the same spectral type but become hotter around B9. The gravity, multiple systems, non-LTE, convection, rotation, opacity, and line blanketing effects have been considered for their possible influence on the observed flux deficiency of B supergiants and giants compared with main sequence stars of the same spectral type.