Example: Light from our tomato hits the eye In the previous example we determined the effective spectrum of light coming from a tomato as the result of the lighbulb/tomato interaction. As we would expect, we receive almost entirely red light only. Now imaging that this light hits our eye, enters the retina and interacts with the three times of cones on the retina. The graph on the left shows the cone response (i.e. signal strength) as a function of wavelength as we have already seen. I have chosen the colours blue, green and red for the beta, gamma and rho cones respectively but do not confuse those colours with the additive colour system primaries. Of course the cone responses are approximately in the regime of what we call "blue", "green" and "red" but they are not very sharp and limited. The response of the rho ("red") cone for example is still present even at a wavelength of less than 400nm (weak but present). Just as in the first example we can now convolute the two graphs to obtain the effective signal coming from each kind of cone. To get the actual signal strength we need to integrate the area under each curve in the resulting graph. For this example we get a signal strentgh of 5.5 for the rho cones, 3 for the gamma cone and close to zero for the beta cone. Our brain performs such an analysis and then bases its perception of colour on the ratio of these signals. In this case we would perceive the tomato as mostly red with a bit of a greenish hue to it.