It doesn't feel like 15 years since the last Leftfield album. I don't even know how long ago it was, though the bands always glacial work rate – an album every five years even at their most prolific – makes new material, at best, a rarity. It hardly seems like a decade and a half since I saw them touring “Rhythm And Stealth” at Glastonbury. So much changes in 15 years. Can Leftfield still be current, be relevant at all, after a decade and a half away from the coalface? Do they exist in a rarified world of isolation, away from the outside world, a self-sealed entity like AC/DC?

Following on from 2011's reunion ; well, lets be blunt, it was no reunion, but half the band starting again and using the bands name to play live, kind of like Oasis without Noel Gallagher, or the Pet Shop Boys if Chris Lowe wasn't there. On paper – and to the ears – it sounded authentic, and real, but it's a bit ersatz - a very very good recreation, but not quite the same. On the other hand, “Alternative Light Source” is classic Leftfield. Sure. It sounds real, it sounds genuine, it sounds real. Leftfields strength always came from a combination of a relentless drum patterns, the insistent urgent pounding, a fierce machinegun bass, and nowhere is this more compelling, more unstoppable than on “Universal Everything”, where's there's a drop and return around four minutes in that at the precise moment I experienced that for the first time, I knew there would be no doubt that this would happen.

It opens with “Bad Radio”. Unlike many, here there's an assortment of guest vocalists, but the words are more just part of the mixture, a human texture, and an air, a feeling. It's hard to pick out individual highlights - “Universal Everything”, and the Sleaford Mods guesting on “Head And Shoulders” are the sound of the city, the sound of traffic lights, trucks, chicken shops, of urban Britain, the insistent, unsleeping heartbeat of a capitalist, working city, and at the same time, also, distant – watching – observing – judging the world as is, with it's relentless, brutal obsession with margin and profit and money, which is, in itself a form of bottom line, besuited terrorism. Endlessly beset by creatures of commercialism.

You might expect the second half – or Side Two, for the older folk – to dip, but then the title track provides a dark interlude, before a final conclusion with “Shaker Obsession”, and the haunting, hesitant “Levitate For You”, which sounds like the muttering of ghosts and the idle chatter of haunted dreams that have been ground to dust through exhaustion and hard fist of an uncaring slavemaster. Is it 15 years already, since the last album? Is it the time where we are back to the grind, and is this the entertainment that comforts? In these times of darkness – spirtiual, emotional, commercial – we need an Alternative Light Source, a path that leads us through the night to the morning.