Introduction:
When a sodium vapor lamp is switched on, the initial color emitted is pink. Sodium vapor lamps are a type of gas discharge lamp that produce light by passing an electric current through a mixture of gases and vaporized sodium metal.

Explanation:
1. Sodium Vapor Lamp:
A sodium vapor lamp consists of a sealed glass tube filled with a small amount of neon gas, along with a larger amount of sodium and mercury. The lamp also contains two electrodes at each end of the tube.

2. Gas Discharge Process:
When an electric current is passed through the electrodes, it ionizes the gas mixture inside the tube. This ionization process causes the gas atoms to release energy in the form of light. The specific colors emitted by the lamp depend on the types of gases and metals present in the tube.

3. Pink Color Emission:
In the case of a sodium vapor lamp, the initial color emitted is pink. This pink color is the result of the combination of the emitted yellow light from the sodium atoms and the emitted blue light from the mercury atoms.

4. Sodium Emission:
When the lamp is switched on, the electric current causes the sodium atoms to become excited and jump to higher energy levels. As these excited sodium atoms return to their ground state, they release energy in the form of yellow light with a wavelength of approximately 589 nanometers. This yellow light contributes to the overall pink color observed initially.

5. Mercury Emission:
In addition to the yellow light emitted by the sodium atoms, the lamp also contains mercury atoms. When the lamp is switched on, the electric current excites the mercury atoms, causing them to emit blue light with a wavelength of approximately 435 nanometers. This blue light combines with the yellow light emitted by the sodium atoms, resulting in the observed pink color.

Conclusion:
In summary, when a sodium vapor lamp is switched on, the initial color emitted is pink. This pink color is the result of the combination of yellow light emitted by the sodium atoms and blue light emitted by the mercury atoms present in the lamp.