The glass light-hows.

Materials. Energy bands. Photons. And why glass is transparent.


Glass pitcher with light rays of words radiating outwards like a light house1-Minute NomNom

Half empty or half full? As far as glass is concerned, it might be neither. And that is the precise reason behind what makes glass transparent.

Why is this so? Put simply, it all has to do with whether light energy is absorbed by a material or allowed to pass through.  This light energy comes in the form of photons, which are the particles that carry light over space. When photons are let through, the material – such as glass – is transparent. When it is absorbed, the material is opaque.
glass cookie jar - glass is transparent because the band gaps do not absorb the light photos, letting them pass through

Going deeper into the science

Dive deeper into the atomic level and it becomes even more intriguing. The different electrons surrounding an atom are at different energy levels, also known as energy bands (see diagram below). For electrons to jump to the next higher level (band), the electrons must absorb enough energy. To fall to a lower one, they must lose enough energy.

example of energy levels and band gapThe amount of energy needed for either is the energy difference between two energy bands, which is also called a band gap. These band gaps are discrete: there must be enough energy absorbed or lost, or the electrons will not change levels (i.e. they do not move halfway or partway). milk cartons - examples of materials that are opaque as band gaps absorb the photonsThis is what determines whether a material is transparent or opaque. When materials have band gaps that can absorb the light energy in photons, these materials – such as the milk cartons above – look opaque when light falls on the materials.

For glass however, the band gaps are larger. Photons do not have sufficient energy to excite the electrons to leap up to the next level. The light simply passes through, giving glass its transparent quality and finally solving the old conundrum: the glass is neither half full nor half empty when it comes to photons and band gaps.

transparent glass bottles are sometimes used to symbolise purity Companies have taken advantage of the transparency of glass to influence how their products are perceived. Top-end bottled water, soda and alcohol brands, for example, sometimes use glass to suggest that the water inside has very high levels of purity and cleanliness.

Feed Me!

What types of foods do you usually put in glass containers? Why do you do it? Tell me about it!

Screen Shot 2015-01-10 at 6.02.39 pmLike this? We are very transparent about science so like me to discover more. All you need is a minute a day to explore the world’s marvels through the phenomenon of food!


photos: in order – depositphotos/konstantin3springfield; depositphotos/kee_zaakarandaev

Leave a Reply