The Hoerengracht, National Gallery, London

Listing the likenesses between modern art and prostitution would take more space than we have here and be just too easy. Not so for Ed and Nancy Kienholz, though, which is why the National Gallery is currently home to a chunk of Amsterdam's red-light district, in the form of the Kienholzes' Hoerengracht.

Lest the pair have passed you by, Ed Kienholz was, until his death in 1994 at the age of 66, an American installation artist. His wife and collaborator of 22 years, Nancy Reddin Kienholz, has continued their joint work since, this being made up of gruesome, life-size tableaux built to play out the nastier moments of 20th-century history: Nazism (the Kienholzes divided their time between Idaho and Berlin), post-Pill promiscuity, urban alienation and dogging on the back seats of cars. Earlier this year, I stood inside an interactive Kienholz installation called Pedicord Apts at the Weisman Museum in Minneapolis – the rebuilt corridor of a seedy hotel, through whose bolted doors waft sounds of the lives inside: women weeping, men shouting, Hopper-ish lonelies muttering to themselves. The effect is unpleasant and, to those of us raised not to listen at doors, embarrassing; not least because your own presence sets off the work's soundtrack, leaving you somehow complicit in its horrors.

If Pedicord Apts hints at the voyeurism inherent in looking at art, then The Hoerengracht rubs your nose in it. And, potentially, other parts of your anatomy as well. The Herengracht, or Gentlemen's Canal, is home to Amsterdam's prostitutes, who famously sit in windows to ply their trade. Add an aberrant Dutch O and the area becomes the Hoerengracht, or Whores' Canal. Art-wise, the district is interesting in two ways. First, the idea of painting as a finestra aperta, or open window on another world, dates back to Alberti and 15th-century Florence. Looking at a semi-clad lady in an Amsterdam vitrine and a painting at the nearby Rijksmuseum are arguably the same thing: fantasising at a price, indulging in what sociologists call "commodification".

While this might be true anywhere in the world, the likeness has a particular resonance in Amsterdam. The Dutch are a mercantile people, a trait apparent in Netherlandish art. Vermeer's Girl with a Pearl Earring is a portrait both of a person and of a commodity. The overlap between the two – the idea that the young woman, her lips slightly parted, might, like her pearl, have a price – is what lends the work its sulphurous beauty. Netherlandish painting and the windows of the Herengracht suggest that there is an identifiably Dutch way of seeing, to do with a candour about the link between sex and cash.

Which brings us to The Hoerengracht. As I've said, this is a rough re-enactment of Amsterdam's red-light district, its lanes and windows peopled with mannequins cast from the Kienholzes' friends; one, sensibly dressed, looks like Her Majesty the Queen. The lights of the Sunley Room have been papered over to suggest night, and tinny music is piped through speakers. Walking through the Herengracht is (I am told) deeply embarrassing. Walking through The Hoerengracht is shaming because it is so painless. All the nastiness of prostitution, the pathos and the degradation, have here been mimetically sanitised by art. None of these ladies is going to call out to you, none to die of drugs or STDs. This is voyeurism without a price, save for your sense of self.

And so what? I must say that, in other circumstances, I'd have found the Kienholzes' work annoying. Being so blatant about something so blatant cancels its power. Putting glass boxes over the prostitutes' faces makes the whole open-window thing too obvious; it suggests an uncharacteristic loss of Kienholzian confidence. I'm also fuddy-duddy enough to disapprove of museums such as the National Gallery – temples of old art – having to justify their government grants by being seen to play it modern.

So I'm surprised to find that I enjoyed The Hoerengracht, not for the work itself so much as for the light it cast on the handful of Old Masters shown alongside – in particular, a tiny oil painting on copper of A Man Offering Gold and Coins to a Girl by the 17th-century Hague artist Godfried Schalcken. Part of the point of this work is its size: looking at so small an image forces us into the kind of intimacy it depicts. In different media and on a very different scale, Schalcken and the Kienholzes manipulate us in the same way. All art, they say, is prostitution, all art lovers tricks and johns.

National Gallery, WC2 (020-7747 2885) to 21 February 2010