I think it was just a normal spirit. Spiritual energy is at a higher frequency, and many times, they can appear in a dark room and appear glowing because their energy resembles that of light itself. Now I'm no scientist, but when one light is stronger than another light, the strongest light is more visible and the weaker light appears less visible or none existent. This is what our eyes do, everything we see is formed from light. No light = no sight. For instance, use a weak flashlight and direct it toward a bright light. The weak flashlight won't show. Shut off the bright light and you can see the shine of the flashlight again. Since spiritual energy is so similar to light energy (in relation to how human sight works), I think this spirit's energy canceled out your flashlight's shine.
Many times when a spirit forms and it is of a darker energy, it can make the corner of a room appear dark. This isn't because it is absorbing light but because the energy of the spirit is overcoming the energy of the light in the room. Since it's energy is darker, it appears darker where the spirit stands. Our eyes are designed to pick up the colors of light that reflects off of objects (and black is when no light is reflected) but a spirit (that is not tangible) has no physical surface to reflect light off of, therefore light has no true effect on a spirit.
What we see when a spirit manifests is beyond scientific explaination, therefore in my own theory, when a spirit manifests, the energy is it's own light creates spectral colors directly, like that of a television or computer screen.
I would love to hear any critiques on my theory, as I have never actually had an opportunity to share it.
I hope it helps you out Micah.