Luminous intensity explains: Luminous intensity is a quality of your lens. The farther the aperture can be opened, the more light can fall through the aperture, so in theory you will be making sufficiently exposed images even in low light. So the lens is bright, or fast, because you can illuminate with shorter times.
Problem with photographing with open aperture
Open aperture, so the aperture as far as possible open, is usually never 100% sharp – but is not so bad in most cases, because you will rarely photograph with open aperture, in order to have the sharpest possible picture – but just to play with blur. The quality varies from lens to lens and to find out you have to test yourself when and how your lens is as sharp as you want it: choose the same subject (best on camera tripod), same focus point, different apertures, take pictures, watch, rate yourself what you like and what does not.
Solution: So you should not make landscapes with open aperture, where the whole photo should be sharp, but get you a tripod. You blend a bit, so instead of the maximum aperture f / 1.4 you shoot with 1-2 f-stops less, e.g. Aperture f / 1.8 or f / 2.0. For landscape photos usually more. Sun laughs, Aperture 8. For portraits, the whole thing usually does not really matter, but even here you can only test further – and it depends very much on the nature of your photography and how important sharpness rather than blur in it.