Philip Hensher: Greatness that I didn't even have to pay for

It was a noble gesture to make this marvellous Kobke exhibition free

Easy to love and difficult to pronounce, the 19th-century Danish landscape painter Christen Kobke should be better known than he is. And at the moment there's an exhibition of his luminous art at the National Gallery. It's almost entirely made up of major borrowings from Danish institutions, which have been very generous. Any visitor will leave thinking Kobke was an important and visionary painter; the rooms sing with the Danish sky.

Round the corner, there's another terrific exhibition at the National Portrait Gallery (NPG). I love Indian portraiture more than almost anything, and this survey is magical, again, with some astonishing loans from private collections and institutions. Two highlights: the two versions of the terrifying image of the dying Inayat Khan, from Boston and Oxford, and a ravishing pair of Nainsukhs, that wayward genius of the late courtly style.

Two brilliant exhibitions. We're used to London hosting one fine loan exhibition after another, and maybe take them a little bit for granted. These two, however, are even more impressive for one reason: they are both free to the viewing public. The two galleries have gone to immense effort, secured some exceptional loans, and without any prospect of making money from ticket sales.

It's a fine line that museum directors tread. In a week when arts professionals launched a manifesto aimed at persuading the Government to sustain levels of spending, the question of widening access raises itself. Christen Kobke and Indian classical portraiture are not mainstream topics for an exhibition; to many visitors, they may not be familiar, or may seem "difficult" in some way (I went round the Indian show with a magnifying glass, and was very glad of it). The National Gallery and the NPG have taken a brave decision, as they often do, to sacrifice a substantial tranche of income, and make two fascinating subjects available for nothing. An interesting counter-example is at the Royal Academy, a paying exhibition of that valuable but slightly forgotten 18th-century topographical artist, Paul Sandby.

In both cases, an institution is taking its obligation to illuminate an obscure corner of art history, hoping people will either wander in, in the case of Kobke, or take a double ticket with the blockbuster Van Gogh show downstairs at the Royal Academy.

Institutions such as this nowadays derive a large part of their income from paying exhibitions. It would be very easy indeed for an institution to follow a long way behind popular taste, and supply a steady diet of Monet and the impressionists, surrealism and the pre-Raphaelites. A truly cynical director could pull together 20 impressionists from his permanent collection, give it a name and a ticket fee of £10, and sit back and watch the public forming an orderly queue.

Instead, we should be hugely grateful that they boldly venture into Danish landscapes, hyper-real Spanish religious sculpture, quilt-making and Indian portraiture – all recent or current examples. Access doesn't always mean accessibility, and those museums and politicians who interpret "access" to mean pandering to what the mass of the public already know and like are cowards.

It was a noble gesture to make this marvellous Kobke exhibition free, whether it was a decision reached by the gallery or a condition imposed by lenders. I'm sure the tickets to a paying show would have sold themselves. But, for whatever reason, it's been agreed that we can see these wonderful exhibitions, like the great collections around them, for nothing. Sometimes we forget how lucky we are. I've already been three times.

Parliament should be kept in the dark

Did you turn your lights off? On Saturday night, for Earth Day, you were recommended to switch off your lights for an hour. All sorts of public officials turned off the illuminations of iconic buildings in cities all over the world. I was at the home of my friends Julie and Jonathan for dinner, and we indeed sat in picturesque candlelight for an hour. I said nothing at the time, but have to admit I forgot about it, and had left my windows blazing with burglar-deterring brilliance.

No idea if this does anything for electricity supply, or whether this endeavour will be cancelled out by the next commercial break of a television soap opera. But it did make me wonder why it is, and when it started exactly, that we thought it was a good idea to illuminate the Houses of Parliament, say, the second the sun went down.

Many public buildings contain stern and worthy admonitions to turn lights off within the building; quite a lot of them are wantonly wasteful with outside illuminations. I rather dislike the way central London has been turned into a son-et-lumière display, but mostly on aesthetic grounds and because it confuses the birds no end. For fiscal reasons, and for environmental ones, too, the practice is impossible to defend.

Let the Houses of Parliament sink back at night into the dark, brooding presence on the Thames they were always meant to be.

At least there's one person who likes you, Uma

Oh dear. How embarrassing. Uma Thurman made a film, Motherhood, about the humorous adventures of a harassed mother in Manhattan and her two toddlers. It was released in the UK, and smashed almost all box office records – in the wrong direction. In its first weekend, it earned all of £88. On its first Sunday, one person went to see it.

I keep wondering about that one person – how sad and lonely must their life be, to spend a Sunday evening in an entirely empty cinema, watching an Uma Thurman vehicle both whiny and aggressive? (Even its trailer sets your teeth on edge with its sheer horror).

I once found myself quite alone in a Cambridge cinema watching Last Year at Marienbad. The interval came – it is quite a lengthy film. The ice-cream lady walked to the front of the cinema with her goods. We regarded each other in silence. After five minutes she departed, and the film began again. It was quite an English moment.

But at least afterwards I had seen a masterpiece by Resnais. That solitary observer of Motherhood had no consolation. I guess anyone who it was likely to interest or engage was probably at home wiping up poo, dribble or puke, rather than in a cinema watching a film about these important subjects. The last word went to the producer.

"Think how much crap succeeds at the cinema," she said reprovingly, with the possible implication that her unloved movie fulfilled a recognised criterion.