I have been saying all along that it is electromagnetic waves in the visible or near visible spectrum causing the effect, otherwise the bluetack would not work.

I have been saying all along that it is electromagnetic waves in the visible or near visible spectrum causing the effect, otherwise the bluetack would not work. As to saying that radio is light, if calculating the propagation speed of a radio wave, you don't talk about its speed of radio, you talk about its speed of light. In many technical contexts, light is one of the default terms. Also, there would be no need for the term 'visible light' if light could not be used to describe electromagnetic radiation outside the visible spectrum. Infra-red and ultra-violet are commonly thought of as light and you can even create lensing optics for radio waves and for x-rays. http://www.rozendalassociates.com/Luneberg/index.htm http://www.rozendalassociates.com/Luneberg/index.htm https://www.imt.kit.edu/english/236.php https://www.imt.kit.edu/english/236.php