In W.I.T.C.H. (the original comics from which the animated series were based on), Arkaam the White Queen turns out to be a despotic bitch. Her magical artifacts are also definitely light or fire based. An earlier villain, Tridart, a servant of Nerissa, was angel themed and white, but his powers were ice based.
Kandrakar keeps a prison, the Tower of Mists, whose inmates are complete monsters. Their cells are tailor-made to mind rape them into submission with Irony (the magic stealer Phobos was closed in a magic-absorbing cell, Cedric, the in-universe Prince of Lies, had been imprisoned in a cell made of lies, et cetera). Apparently it's so bad that Phobos preferred a Fate Worse than Death to return in there...
The Angelus from the The Darkness/Witchblade universe. Unquestionably a force of light and law. It just so happens that the Angelus is a completely sociopathic entity that believes the world should be run by her light and her laws.
In an old issue of Superman, the Man of Steel confronted seeming angels, standing guard before the gates of Hell. After he worked out the truth and threw off their illusions, he asked the Space Policeman who took them away why they hadn't changed. The cop calmly told him that they really did look like that.
While Karolina Dean of Runaways is heroic; her parents, who shared her light powers, were supervillains.
From the X-Men books there's Vulcan aka Gabriel Summers, an Omega-level energy manipulator whose powers frequently manifest as light and flames. It's played to the hilt in his confrontation with Black Bolt at the climax of War of Kings.
Air Walker, the angel themed herald/former herald of Galactus. He wasn't that good in a lot of his showings.
Overlaps with Cybernetics Eat Your Soul: most of the times Air Walker appears, he's a robotic rebuild of the original, who was a member of the Nova Corps and a decent person before he signed on as Galactus's herald.
Stardust, a being of pure (and bright blue/white) energy and Galactus's latest herald, is also quite Ax-Crazy, insisting on slaughtering the entire population of any world Galactus consumes, even though Galactus himself has no interest in killing the people (though he has no particular interest in not killing them either).
Inverted and then played straight in Cerebus. Prior to his religious conversion, Sim depicted a creation myth in which the female Light was essentially raped by the male Void in which it resided, causing the Light to completely shatter and form the physical universe. After his conversion, the male void became God and the female Light became YHWH, God's Adversary. Cerebus is physically dragged into the Light after his death in the last issue, screaming for God to save him.
Green Lantern plays with this a little. Certain "colors" in the "Emotional Spectrum" are more evil than others. Red (rage), orange (greed), and yellow (fear) are mostly evil, but green (willpower), blue (hope), indigo (compassion), and violet (love) are mostly good. However, black is so evil it makes all lights look good by comparison, even the evil ones.
In technicality, all colours are neutral, and "good corps" had their own morally inconvenient moments. The Star Sapphires, for example, have a history of Love Makes You Crazy and the Guardians have caused many problems. Blue Lanterns are all good, but their light is very limited in terms of power, so they are often incapable of doing much, while the Indigo Tribe has mercy killed many people, and it is composed of sociopaths brainwashed by the Indigo light anyway.
We can safely add the White Light entity to the list now, thanks to the amount of morally ambiguous acts it has made, such as killing a couple because they love each other and would not obey to its command and separate.
Blue Lanterns will show you visions of hope, but its really just anything that will make you feel hope whether it has any truth to it or not (though presumably plausible visions are more effective than implausible ones).
Even the Black Lanterns of all people play this up. Their outfits have a lot of white in them, and their powers are basically white/silver light.
In the first issue of the Mice Templar comics, (nocturnal) mouse children are told scary stories about the "world of day".
Snowflame, a one-shot villain from The New Guardians, is perhaps the strangest example of this trope. By smoking cocaine (really) he uses what appears to be light manipulation/white flames, and has a white motif, notably his hair. He is also an Ensemble Dark Horse, by the way, thanks to the sheer strangeness of using a drug as fuel for his powers.
The sun like creatures known as "thristies" in Marvel's Kool Aid comic.
In one of Alan Moore's issues of Swamp Thing, John Constantine wonders why everyone thinks of angels as comforting, confessing to the reader that they scare the shit out of him. They do indeed seem to be not so much unalloyed good as merely preferable to the demons.
Taken to its literal extreme in the comic book "The Light," where looking at any light connected to an external power source (lamps, TVs, your computer...) causes you to, quite painfully, incinerate from the inside out.
Some of the women filling the role of "White Queen" in both Marvel (Emma Frost) and DC (Amanda Waller) while having been with the good guys at times, have also been people who have at times gravitated towards committing immoral acts for their own goals.
Emma Frost was more than someone who gravitated towards immoral acts - in her early days she was a straight up Super Villain and quite sadistic. The Dark Phoenix Saga only happened because Frost along with Wyngarde were messing with Jean's head; they just didn't realize they were out of their league. When she resurfaced she spent a good while as a recurring foe of the X-Men and the Big Bad of the New Mutants and Xavier's Evil Counterpart - she recruited newly discovered mutants to train in the use of their powers to become the Hellfire Club's army. During that era - before we'd met Apocalypse and when Magneto was on the 'face' side of the Heel-Face Revolving Door - Frost was the X-Men franchise's foremost villain.
Dark Is Not Evil Marvel hero The Shroud, who traded his sight for scary shadowy superpowers, once faced an evil preacher with light powers.
In Fables the manifestation of Hope is depicted as a beautiful woman with a shiny aura. She does admit though that both good and evil have hope. Indeed, one of Hope's paladins speculate that darker impulses like revenge are more likely to get motivation from that emotion.
Dynamite's 2012 The Shadow series has both this and Dark Is Not Evil with The Shadow fighting a Knight Templar woman nicknamed The Light.