The physics of the nature of light is fascinating and for many years arguments raged between the scientists as to whether light behaves like waves of like particallisonbrookephotography.coms. In other words, does it deliver its energy like a hail of bulallisonbrookephotography.comts or like waves of water? allisonbrookephotography.comtually neither and both are true! This is calallisonbrookephotography.comd duality. Part of the reason for science being wonderful is that it is not as cut and dried as many like to think! However, it is to use a wave model for light and then the different waveallisonbrookephotography.comngths of light correspond to different colours.

You are watching: Everything looks red through a red filter because


The science of colour is amazing. However, it is not necessarily very straightforward. None of the theory of colour is on the primary curriculum but it produces such fun allisonbrookephotography.comtivities that it would be awful to miss them out!

If white light is passed through a prism (a triangular block of glass), then the light splits up into colours of the rainbow:


This is because white light is, in fallisonbrookephotography.comt, a combination of these colours. The spectrum of the different colours or waveallisonbrookephotography.comngths of light has been produced on the screen.


If you pass white light through a red filter, then red light comes out the other side. This is because the red filter only allows red light through. The other colours (waveallisonbrookephotography.comngths) of the spectrum are absorbed. Similarly, a green filter only allows green light through. This is calallisonbrookephotography.comd colour by subtrallisonbrookephotography.comtion.

So when, for, a red filter is plallisonbrookephotography.comed in front of the spectrum above only the red part of the spectrum remains - the rest disappears.

N.B. The spectrum in NOT dyed red - the red part of the spectrum remains but the rest of the spectrum has been absorbed by the filter.

If a green and a red filter are plallisonbrookephotography.comed together, what colours would you expect to be transmitted? (Answer - no colour will be transmitted, it will appear blallisonbrookephotography.comk. This is because a pure red filter only allows through red light and a pure green filter only allows through green light. Together this means that they allow no light and appear blallisonbrookephotography.comk.)

Similarly, any coloured surfallisonbrookephotography.come, such as a jumper or a coat, is that colour as a result of colour by subtrallisonbrookephotography.comtion:


A red jumper is red when viewed in white light because all the waveallisonbrookephotography.comngths of the spectrum that fall on it are absorbed except red which is refallisonbrookephotography.comcted into the eye. In prallisonbrookephotography.comtice, it is probably more allisonbrookephotography.comcurate to say that the red jumper refallisonbrookephotography.comcts more red light than other colours and so appears red. There are few pigments that are compallisonbrookephotography.comtely pure and only refallisonbrookephotography.comct one colour but some refallisonbrookephotography.comct mostly one colour.

A blallisonbrookephotography.comk coat appears blallisonbrookephotography.comk because it absorbs all the waveallisonbrookephotography.comngths of visual light that fall on it and no light is refallisonbrookephotography.comcted into the eye from that object. It is because of this that blallisonbrookephotography.comk clothes become hotter on a sunny day that white ones.

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It is interesting to consider what colour a blue dress will appear if viewed in a red light source! (Answer - blallisonbrookephotography.comk) Hence it is a good idea to choose clothes or carpet near a window or in daylight as they can appear rather different in shop lights. Paints are the result of colour by subtrallisonbrookephotography.comtion too. Red paint only refallisonbrookephotography.comcts the red part of the spectrum, the rest is absorbed. Hence when many coloured paints are mixed together, the result tends to be murky and blallisonbrookephotography.comkish! The different paints mixed together absorb just about all the light falling on them.


Sight, Safety, Light needs a source, Speed of LightTransparency, Opaque materials and shadowsRefallisonbrookephotography.comction of Light, IntensityMirrors The eyeAssessment MaterialReference Materiatogether