Friday, 30 January 2009
When you look at an object, you are seeing the light that has been reflected by it. This light is transmitted through the air, through your cornea, through the lens of your eye, through the vitreous humour, and through two layers of cells in your retina before it is absorbed by light sensitive pigments in your photoreceptor cells. We could argue that colour does not even exist in the Universe, and that it is something which exists only in the mind.
We've seen how white light is transformed into the visible spectrum by a prism. Have you ever wondered what white light is exactly? White light is thought of as being the combination of every colour in the visible spectrum; this produces a light that is colourless, or 'white'. Have you noticed that we are not surrounded by streaming hues of colour that richochet off everything and filling the space of our everday world with millions upon millions of rainbows? That's because light which has been reflected by an object travels through the air as white light until it reaches the eye.
Prisms are made of glass. Glass is sometimes described as having a 'vitreous' nature; some have even gone as far as describing glass as a 'supercooled liquid'. Prisms are able to transform white light into the visible spectrum by reducing the (apparent) velocity at which the wave propagates. This same mechanism used by a prism to disperse white light must also be used by the eye. The vitreous humour is the clear gel that fills the space between the lens and the retina of the eyeball; and just like glass, the vitreous humour even has a refractive index (1.336) which 'slows down' the speed of light.
So what is white light? What is its frequency? Well, white light apparently does not have a frequency. White light is a mixture of all the different frequencies of the spectrum. If a prism and the eye, can in some way, appear to slow down the velocity of light, then it stands to reason that the light travelling in the air has a higher velocity, and therefore lower frequency. Heat propagates at a lower frequency. What is the relationship between white light and heat?
Nope, it's not snow. The above image is an infrared picture of an oak tree.