Nomercy448

Reflected light and dispersion, and the coincidence that our photoreceptors are highly tuned to gather its particular "hue". Bead blasting creates a highly light dispersive finish, and overall, the barrel is "grey". In low light, our eyes switch over to rely solely upon the RODS for photoreception, which only see in grey scale. The lighter grey an object is, the higher intensity it appears to the Rods.

Additionally, your eye will exhibit a "saturation" effect where the rods start to turn off because of the degree of light exposed to them (degree in terms of "temperature", aka colloquial terminology for frequency). This is the same reaction to getting a flashlight shined in your eyes in the dark, previously you could see fine because the majority of your rods were active, the burst of light shuts them down, so now you're stuck with night-blindness until your eyes adjust back to the darkness. Rods are kinda like the big fluorescent lamps at stadiums, they turn off quick, but take some time to come back on.

So it's not really that your barrel is glowing, it's that it washes out your eyes and makes everything else seem darker. Your bright grey barrel, even though it's a matte finish, reflects a high grey that saturates some of your rods. To "cool" the light sensitivity, your rods switch off and everything else gets darker, except your light saber.