White light is the name given to visible light that contains all wavelengths of the visible spectrum at equal intensities.
- The sun emits white light because sunlight contains equal amounts of all of the wavelengths of the visible spectrum.
- As light travels through a vacuum or a medium it is described as white light if it contains all the wavelengths of visible light.
- As light travels through a vacuum or the air it is invisible to our eyes.
- The term white light has two meanings. It can refer to:
- The human eye also sees white when the wavelengths of light corresponding with the three primary colours red, green and blue (RGB) are projected onto a neutrally coloured surface.
- White light appears coloured when some wavelengths of light are reflected by the surface of an object but others are absorbed.
- Artificial light sources typically emit light with an uneven distribution of wavelengths or intensities and so do not emit white light.
- Whilst there is no single, unique specification for white light, it is reasonable to argue that in any specific situation:
- White is the lightest possible colour.
- White is an achromatic colour, meaning a colour without a hue but with maximum saturation and brightness.
Why do light bulbs glow if light is invisible?
- Incandescent light bulbs work by passing an electrical current through a fine tungsten filament that has a high electrical resistance.
- The resistance causes electrons within the filament to heat up and to appear a very bright yellowish-white colour. This colour is produced by:
- The appearance of the surface of the heated tungsten.
- Refraction, reflection and dispersion as light encounters microscopic water droplets and the surfaces of particles of dust on its journey from the light bulb towards an observer’s eyes.
- Refraction, reflection and dispersion in liquids and solids within an observer’s eyes before light reaches the retina.
- Independent of these observed properties, the filament also emits a full range of wavelengths of light that propagate without encountering obstacles and so remain entirely invisible to an observer.
- The light emitted by a tungsten bulb spans wavelengths between 200 and 3000 nanometers.
References
White light is the name given to visible light that contains all wavelengths of the visible spectrum at equal intensities.
- As light travels through a vacuum or a medium it is described as white light if it contains all the wavelengths of visible light.
- As light travels through the air it is invisible to our eyes.
- When we look around we see through the air because it is very transparent and light passes through it.
- The term white light doesn’t mean light is white as it travels through the air.
- One situation in which light becomes visible is when it reflects off the surface of an object.
- When white light strikes a neutral coloured object and all wavelengths are reflected then it appears white to an observer.