Projected Light

Fig.1 shows the overlapping light beams as shown in most books on physics to try to convince the public that white light is composed of all the other colours.

Unfortunately the illustration does not show the actuality, because there are no neat uniform areas of colours as shown.  The light projectors do not project an even circle of colour as shown because the high intensity white beam always shows through the filters.

Consider the following extract: ‘It is an advantage if the projectors are controlled by rheostats, so that the relative intensities can be controlled in order to produce a good white’.  From PHYSICS – An Examination Course. By E. L. Hansen. Hulton Educational Publications Ltd.  In other words, if the physicists cannot obtain the results that they want, they are allowed to cheat. To be fair they don’t understand that it is cheating.

If you look at a Blue filter lying on a white sheet you see an even blue shade across the whole filter. If you shine a light through any filter you get results similar to those shown below.

It is obvious that a considerable amount of white light is coming through the filters. If we re-label the above drawing to allow for this white light we arrive at the following drawing.

In the above drawing we are looking at the combined colour energy levels in particular areas. We are also getting dangerously close (If you are a physicist) to the artists colour mixing principles.

In the ‘Yellow’ area the combination of colours would give a yellow ochre. In the ‘White’ area the combination would give a very light grey. The white intensity from the lamps is very much higher than the white intensity from a ‘White’ screen, and therefore a relatively small amount of white light has a far greater impact than you would expect. Referring back to the chapter on the energy value of coloured light, the white light from the lamps has a probable intensity of at least 10 times greater the yellow light from the filters.

See ‘The Origin of Colour’,  Taper Slit experiment,  Taper Silhouette Experiment.