GL_LUMINANCE

Can someone explain to me what GL_LUMINANCE does I have a texture that doesnt display right unless I do GL_LUMINANCE. I finallyt gave up and just started trying stuff and it worked. I dont care its not a problem but I would just like to know what is the reason why it works

A luminance texture is a single channel texture, where the single channel is copied into the R, G and B component, and A is set to 1, when used. Basically, a greyscale image.

well that would explain why it works -thanks