The psychic blade does not produce any light.
When an object, a spell or any other game feature emits light this is specified in the description, among which "type" (bright or dim) it sheds.
The Flame Blade spell description says:
The flaming blade sheds bright light in a 10-foot radius and dim light for an additional 10 feet.
The Crystal Blade has the following property:
While you’re holding the sword, you can use a bonus action to cause it to shed bright light in a 30-foot radius and dim light for an additional 30 feet, to cause it to shed dim light in a 10-foot radius, or to douse the light.
Twilight and (surprise surprise...) Light domains present some features that use light, and when these have mechanical consequences they are specified:
Corona of Light. Starting at 17th level, you can use your action to activate an aura of sunlight that lasts for 1 minute or until you dismiss it using another action. You emit bright light in a 60-foot radius and dim light 30 feet beyond that.
Twilight Sanctuary. As an action, you present your holy symbol, and a sphere of twilight emanates from you. The sphere is centered on you, has a 30-foot radius, and is filled with dim light.
The quoted text of Psychic Blades refers to shimmering blade: looking at the definition in MacMillan dictionary one can read:
to reflect a gentle light that seems to shake slightly
But the example below is more explanatory, to me:
The desert landscape shimmered in the midday heat.
In my opinion, the authors of this feature poorly chose the wording1 and they intended that the blade is translucent, is made of psychic force and blurs the sight of what is beyond the weapon.
From a "class point" of view, it could be very strange that a Rogue subclass possesses an ability that could easily give away their stealth.
1 What a surprise, again.