Final answer:
Making the wavelengths 'taller' or increasing the wavelength of a spotlight will make the perceived light appear redder. Conversely, increasing the resistance in a lightbulb circuit will result in a dimmer and redder light due to less current heating the filament.
Step-by-step explanation:
When a lighting technician adjusts a spotlight and makes the wavelengths taller, he is increasing the wavelength of the light. According to the electromagnetic spectrum, light with longer wavelengths is perceived as redder, and light with shorter wavelengths is perceived as bluer. Therefore, if the lighting technician increases the wavelength (or makes it 'taller'), the effect on the perceived light is that it appears redder.
In terms of light being emitted from a lightbulb wired to a variable resistor, increasing the resistance generally results in less current flow and therefore a dimmer and redder emission, as there is less energy to heat the filament to temperatures that produce bluer light.
Key concepts to understand from this explanation are the facts that blue light has a shorter wavelength and higher frequency than red light, and that light wavelength correlates with our perception of color, while amplitude (height of the wave) correlates with brightness. For example, during sunset, the light from the Sun has to travel a longer distance through the atmosphere, and due to scattering effects, it appears redder.