What would a manufacturer of fluorescent lamps have to do in order to change his "warm white" lamps to "cool white" lamps? 1\. Change the amount of mercury vapor in the lamp to produce less ultraviolet light. 2\. Change the thickness of the glass tube to get a greater index of refraction. 3\. Change the composition of the electrodes to produce a weaker electric arc. 4\. Change the composition of the phosphor to emit more light at the blue- violet end of the spectrum.

The way a fluorescent lamp works is that there is a low-pressure mercury vapor gas inside a glass tube. When an electric current is passed through this gas, ultraviolet (UV) light is produced. This UV light then strikes the phosphor coating on the inside surface of the glass tube, which in turn emits visible light.

In order to change the color of the emitted light from "warm white" to "cool white," we must modify the lamp's characteristics in such a way that it results in a higher color temperature. This change can be achieved by modifying the light emitted by the phosphor coating.

\(\bullet\) Option 1: "Change the amount of mercury vapor in the lamp to produce less ultraviolet light." - This would affect the brightness of the lamp, not the color. \(\bullet\) Option 2: "Change the thickness of the glass tube to get a greater index of refraction." - This would not have any significant impact on the color of the light emitted. \(\bullet\) Option 3: "Change the composition of the electrodes to produce a weaker electric arc." - This would affect the efficiency of the lamp and possibly its lifetime, but it wouldn't change the color. \(\bullet\) Option 4: "Change the composition of the phosphor to emit more light at the blue-violet end of the spectrum." - This option would actually result in a change of the color temperature of the emitted light, making it closer to "cool white."

Based on our understanding of the process and analyzing the options provided, the correct answer is Option 4: "Change the composition of the phosphor to emit more light at the blue-violet end of the spectrum." This change would shift the color temperature of the emitted light from "warm white" to "cool white," as required by the exercise.