But what kind? That is the question….. A personal theory  – which has been quietly fermenting in my mind for some time – receives its first public airing thanks to a recent meeting I had with an old friend who is also the managing director of a famous publishing house.

He told me that 90% of all ebooks are sold in the UK are sales on the Amazon Kindle platform.

Perhaps that’s no big surprise. The Kindle was first major e-reader on the market and Amazon is the category-killer online bookstore.

But I suspect there is more to it than that. Much more.  Most surprising is that people do not generally read books on iPADS or other devices with backlit screens. Why? Because the Kindle is different. Until the HD Fire (big mistake on Amazon’s part, in my view) the Kindle has relied on reflected not emitted light.

The difference is hard to overstate. When you read a traditional paper book the light that enters your eyes is natural and reflected off the page. When you stare at a backlit screen, the information you receive is artificially produced and emitted like a beam of fire into the back of your retinae.

Wander through an art gallery and the pictures inspire you because their colours filter white light and reflect back into your eyes creating an image which, very often, provokes feelings of empathy in the brain. Empathy is triggered, I suspect, by reflected not emitted light.

Let’s zoom out for a moment. For millions of years our brains have been hard-wired to respond to reflected light – from an awe-inspiring view from a mountaintop to the sparkle of a diamond ring. We do not look directly at the Sun – we cannot because it scorches our eyes. Instead we have evolved to learn through reflections, colours, shadows, hues and haze.

This is still true to life today for those seeking inspiration. People do not think to embark on a mountain hike through the convenience of a virtual reality helmet any more than it is fashionable to wear an engagement ring that sparkles thanks to a series of embedded light emitting diodes. The idea is ridiculous because our brains do not respond to emitted light in the same way that they respond to natural reflected light.

We do not look directly at the Sun – we cannot because it scorches our eyes

It explains why iPADs are lousy as book reading devices, despite all the hype when they were launched that they would replace the Amazon Kindle. It explains why the Kindle has been such an astonishing success. I can read a Kindle without it blasting my eyes with LED radiation. It doesn’t tire them. I find the words inspiring – intriguing – I am curious –  Why? Because they are reflected not emitted into my mind – just in the same way the National Portrait Gallery hasn’t yet (as far as I am aware) mounted an exhibition on backlight LED screens instead of paint or photographs on canvass or paper.

I suspect the same logic runs through why people are happy to pay for content they receive on paper but unhappy to pay for the same content displayed on a screen.

The psychological difference being the way that light is delivered matters even more  because people who consume everything through a backlit screen are, I suspect, being spiritually starved. The problem of too much Facebook, Twitter, computers and TV screens isn’t that addition to news feeds, stock prices, instant messages and tweets is undesirable in itself – addictions of all kinds are and have always been part of the human condition.

The problem is that today our brains are being force-fed data by a blast of manufactured light delivered in a way that appeals to the focused left-hemisphere only, while the right hemisphere  – the one which appreciates the big picture  – the shadows and reflections of everyday living – is sidelined almost to extinction. The right side of the brain  - spiritual, emotional, holistic, empathic self – is being starved by the tyranny of yesterday’s CRT superseded by an LED and backlit LCD revolution.

So next time you wonder what is it about modern living that leaves you feeling empty, cold and undernourished – then simply try switching off the screen and bathe yourself instead in the right kind of light.

So please excuse me, if I now take my own advice.

Very best!