The departure of Roger Waters from Pink Floyd was followed by a classic Lightening and Softening. From mental breakdowns rendered into music and harsh lyrics condemning modern life, Pink Floyd moved to David Gilmour's gentle dreamy soundscapes. Lyrically, the later albums tend to unfocused expressions of good will and an earnest appreciation for life. The remaining angst now seemed more of pose: a mere colour on the palette, not a raw daub of blood. Interestingly, the Waters-lead era (beginning with The Dark Side of the Moon) was itself a Darker and Edgier version Pink Floyd. Before this point, Floyd albums were known for being spacey and psychedelic rather than particularly dark. Indeed, their original Syd Barrett era was downright whimsical at times.
In terms of singing style, In This Moment's second album The Dream, which placed a lot more emphasis on clean vocals than the Metal Screams of Beautiful Tragedy. This was because lead singer Maria Brink wanted to challenge herself with what she (personally) found a more difficult singing style.
One could make a case for this happening to Joy Division after they changed their name to New Order. Not that New Order doesn't have a certain edge to their brand of pop.
The Misfits in the 90s, sort of. The low-budget, dirty hardcore punk turned into cleanly-produced punk/metal. Profane lyrics about sex, rape, and chaotic violence stopped, but lyrics about violent horror movies remain.
Hardcore Techno fans have a huge chip on their shoulder about its lighter and softer cousins: Happy Hardcore and Hardstyle, which charted pretty heavily in the 90s (happy hardcore) and the early 00s (Hardstyle).
The Tubes. The glitter-shock incarnation that did "White Punks On Dope" in the '70s were a far cry from the group that had a hit with "She's a Beauty" in the '80s. Singer Fee Waybill has acknowledged that this was done intentionally. His reason? "Nothing shocks anybody anymore."
This happened to many pop-metal bands in the '70s and '80s as they gained commercial success. An example is REO Speedwagon. Their first album included tracks called "Five Men Were Killed Today" and "Dead At Last." Years later, they would have big hits with the power ballads "Keep On Lovin' You" and "Can't Fight This Feelin'."
American Slang seems to be this for The Gaslight Anthem.
The Velvet Underground have an interesting trajectory in this regard. Their first album—1967's The Velvet Underground & Nico—was a fairly eclectic mix of soft stuff, hard stuff, and hard stuff that sounds soft (consider "Sunday Morning," for instance). The next album, White Light/White Heat, took a definite turn for the experimental and dark (the title track is about amphetamines, and it gets more macabre—often humorously so—from there; John Cale stated that it was "consciously anti-beauty"). However, the third album, 1969's The Velvet Underground, is a lot mellower (if nevertheless experimental) — something the band occasionally attributed to having their equipment stolen before recording —, and finally 1970's Loaded (so called because the label wanted an album "loaded with hits"), which is much softer musically (but also just as experimental and ridiculouslylistenable, proving that Tropes Are Not Bad).
The first two albums by Mötley Crüe, Live Wire and Shout at the Devil, were dark and gritty Heavy Metal albums with lyrics that dealt with things like drug abuse and Satanism. Beginning with their third album, Theater Of Pain, they moved in a more MTV-friendly hard rock direction with rock anthems like "Smokin' In The Boys' Room" and ballads like "Home Sweet Home."
In an intentional case of this trope, Prince's "Lovesexy" was released as a light and fluffy response to the zany, mean-spirited "Black Album," complete with a pink album cover with a flower on it.
Gorillaz followed up his darkest and most depressive work on "Demon Days" with a flashy synthpop album, "Plastic Beach."
VNV Nation's 2010 album, Of Faith, Power and Glory, was very depressive and cynical, but the follow-up, Automatic, is much brighter and more upbeat. The band in general are the trope codifiers of the Futurepop subgenre, the lighter and softer version of EBM.
The Pierces had three dark-sounding, Femme Fatale-like albums out with very little success. Their fourth album, involving gentler songs reminiscent of The Bangles, got them breaking into the mainstream.
A lot of Hip-Hop fans say this is what happened to mainstream rap music. The days of the weed smoking gangstas, and proud to be black Afrocentric political rappers with their gritty Justified crime tales, and socio-political street knowledge were long gone. Only to be replaced (circa early 00's) by champagne sipping pimps, and playas, who love to rap about wealth, cheesy love songs, and club anthems.
Madonna's Confessions On A Dancefloor and it's sequel, Hard Candy.
Synthpop duo Future Perfect's first album, Dirty Little Secrets, is dark, angsty, and depressing at times. Their second, Escape, looks to be headed in the upbeat and energetic direction, by the previews.
Avenged Sevenfold, although their music is still dark-and-edgy by general music standards.
Many thrash metal bands went in this direction around the time of the grunge explosion, partially to keep up with the times and partially because the bandmembers themselves were growing tired of the musical style they were playing. During the last decade, however, this has been subverted by many of these same bands.
Testament subverted this trope after their "lighter and softer" The Ritual flopped. Demonic, in particular, borders on being a full-blown death metal album.
Oshare kei is this to Visual Kei—oshare kei tends to be much lighter and more playful than other visual genres (expect lots of bright colors and pastels), and, while most other VK subgenres tend to play some form of Heavy Metal, oshare kei generally prefers Pop Punk. Just compare, for example, D (kote kei, the most common VK subgenre) with An Cafe (oshare kei).
Played straight, then modestly averted with Underoath. Those familiar with their commercial successes They're Only Chasing Safety and Define the Great Line might be shocked upon listening to their first two releases, Act of Depression and Cries of the Past, both of which are full-blown Death Metal albums. The aptly-titled follow-up The Changing of Times marked a break away from their original Death Metal sound into the more melodic and accessible Post-Hardcore sound they became known for today.
However, after Only Chasing Safety, their (relatively) Lightest and Softest albumnote containing lines such as "Sleeping with the girl next door, I always knew you were a sucker for that" that were a stark contrast to the punishingly dark themes on the first two albums such as suicide, abortion, rape and damnation marked by a change in vocalist from their original Unintelligible Death Metal shrieker to more ear-freindle Hardcore vocalist Spencer Chamberlain and switch to a more radio-friendly "screaming verse, singing chorus, rinse and repeat", each release afterward was noticeably darker and heavier than the last. The departure of long-time drummer and clean singer Aaron Gillespe has left the band in a position between the dissonant Death Metal of the debut and the commercial melodic Hardcore of Chasing Safety, sporting a Doom Metal-esque sound with emphasis on neither heaviness or melody.
The Break Up, while still slightly dark, are definitely lighter than Severina X Sol's previous bands; Diva Destruction, Fockewolf, and Cylab.
Believe it or not, Def Leppard was once considered one of the major bands of the new wave of British metal alongside bands like Iron Maiden and Motörhead. These days, most people only know the band for their radio-friendly Hair Metal hits that started with their third album, Pyromania. The members of Def Leppard openly admit that they adopted a softer and more mainstream sound in an effort to become more popular and successful. It worked, big time.
Country Music band Lonestar. They were a bit edgy and more rocking on their first album; the second was smooth, almost Eagles-esque; the third was anchored by the Power Ballad "Amazed" and other songs like it; and all the successive albums contained a mix of "Amazed"-style power ballads (e.g. "Not a Day Goes By", "Let's Be Us Again"); mushy, bland, family-friendly, soccer-mom-targeting fare (such as "I'm Already There", "My Front Porch Looking In", and "Mr. Mom"), and otherwise safe, totally de-fanged lite-country-pop. It's hard to believe that this is the same band whose first #1 hit, "No News", had a Ku Klux Klan reference Bowdlerised from it.
Acid Bath could have been said to have done this with their second album, which toned down the abrasive sludge, death metal, grindcore, and post-hardcore elements of When the Kite String Pops while bumping up the stoner, blues, gothic rock, folk, and country influences. Of course, given that it was Acid Bath, Paegan Terrorism Tactics was still incredibly dark and nightmarish, just a lot more prone to Lyrical Dissonance. It was also a perfect example of Tropes Are Not Bad and how to pull this trope off the right way.
Breaking Benjamin did this somewhat. Their first two albums, Saturate and We are not Alone, were both had heavier Alternative Metal influences, drawing inspiration from Alice in Chains and Tool. Their next two albums, Phobia and Dear Agony, had more of an alt rock/grungy sound and were a little bit softer musically. Lyrically though, they were about the same, with the later two albums possibly even being a slight bit darker than their first two.
Tricia Brock's departure from Superchic[k] saw her take this route, ditching the rock sound and teen angst inspired lyrics.
There's two versions of Andrew Belle' "Sky's Still Blue": The original and the version made for a commercial. The revised version is significantly fluffier, with a lighter tone and changed lyrics, compared to the melancholy original.
In the beginning, Sevendust gradually got lighter with each release. Their Self-Titled Album was very aggressive, raw metal with some songs bordering on Crossover Thrash, a far cry from the more accessible sound of their later albums. Home and Animosity featured more clean vocals and less screaming, but were still relatively heavy. Seasons and Next, however, really toned things down, with half the songs being borderline radio rock that wouldn't sound out of place on a Linkin Park album. Which makes it rather jarring to hear the album that came after Next, Alpha, which is their angriest, loudest, and heaviest album to date.
Faith No More really had no direction to go but Lighter And Softer after the nightmarish Angel Dust. King For a Day, Fool For a Lifetime had its share of disturbing and brutal metal tracks ("Cuckoo for Caca", "Ugly in the Morning"), but the contrasting songs were noticaebly way more laidback, usually alternating between Alternative Rock, lighter takes on Grunge and Novelty Songs in the styles of Jazz and Pop. Album of the Year mostly followed suit, with the occasional Angel Dust-esque metal number ("Collision", "Last Cup of Sorrow", "Paths of Glory") surrounded by more upbeat Punk and Alt Rock tracks as well as experiments with ambient electronic sounds. Though both of these albums came after the departure of original guitarist Jim Martin, they are still noticeably Darker and Edgier than Introduce Yourself and The Real Thing.