Endovior, I don't believe mindblades provide illumination.
One of the concepts of the soulknife is as an assassin and I believe they can hide with their mindblades going without giving away their position.
Here is the text on the powers of the mindblade
Mind Blade (Su)
As a move action, a soulknife can create a semisolid blade composed of psychic energy distilled from his own mind. The blade is identical in all ways (except visually) to a short sword of a size appropriate for its wielder.
Are you thinking of it as similar to the magic weapon illumination?
Light Generation
Fully 30% of magic weapons shed light equivalent to a light spell (bright light in a 20-foot radius, shadowy light in a 40-foot radius). These glowing weapons are quite obviously magical. Such a weapon can’t be concealed when drawn, nor can its light be shut off.
However even psionic weapons don't get that optional benefit, just the drawback of some being mentally audible.
Mentally Audible
Fully 30% of psionic weapons telepathically mutter, croon, recite battle poems, scream, or produce other mental “noises” when first drawn, at first blood, or when they slay a significant enemy. Such a weapon cannot be concealed from creatures within 15 feet when it is drawn, nor can its mental “soundtrack” be curbed.
I think it might be an aid to the game however if the party had an easy access to a source of light and I could see a glowing mindblade as being consistent with the class image.
I will give you the choice of either having it be the default no illumination or have the visual of the psychic energy be equal to a constant light effect.