I added a glow to white text and the glow made the region slightly darker. If I increase the intensity, then I get a bright white centre but the area surrounding the centre is darkened which is also undesirable. Why would the glow effect produce a darkening?
The left 5 in the image below is the original and the right 5 is with the default glow effect added. The effect is subtle but it's darkening and not the expected lightening.