it depends, with the Alpha, on the program your using. since I've had to do texture adjustments to my own taste for so long, I'm used to thinking of how to adjust the alphas, now.
an alpha, in my art program's case, is actually a transparency level over the glow areas. to decrease the brightness of the deflector surround, you should make that particular area more opaque.
also, from the pictures, the surround is in various shades of white. greyscaling doesn't work on whites, it would have to be colored first, then greyscaled. use a dull color for the surround if your gonna retain the brightness level of it so as not to mess with the alpha level.