Hid
As a thought, it isn't just Xenon gas in them. D2S bulbs have a salt mixture inside them that give them their colour and brightness. As the electrical arc flows, the bulb heats up. This in turn, heats up and liquefies the salts, turning them into a plasma. From HIDPlanet:
What are some of the salts used in HID bulbs
Common Salts and their colors for HID
Sodium Iodide - White
Thallium Iodide - yellow crystals that become red at 170oC
Scandium Iodide - yellow powder
Dysprosium Iodide - deep yellow powder
Indium Iodide - deep red-brown color
Mercury Iodide - Yellow
The last one may or may not be added, but it may form due to the presence of iodide from the other salts.
More rare salts:
Cerium Iodide-Yellow
Neodymium Iodide - Green
Holmium Iodide - yellow
Erbium Iodide - Pink
Thulium Iodide - Yellow
Gadolinium Iodide - yellow
Ytterbium Iodide - yellow
Which are the most common salts?
The main salts in 4300K bulbs are Scandium Iodide and Sodium Iodide, Dysprosium Iodide is also added to some bulbs. While in higher temperature bulbs, more Indium Iodide is used. This is what gives the salts in those bulbs their red color. It also is really expensive and hazardous to use, which is what gives them their cost.
The exact mixture of salts is unknown, as each company has its own proprietary formula. Trace salts can be added to flesh out the spectrum some, improving CRI.
Common Salts and their colors for HID
Sodium Iodide - White
Thallium Iodide - yellow crystals that become red at 170oC
Scandium Iodide - yellow powder
Dysprosium Iodide - deep yellow powder
Indium Iodide - deep red-brown color
Mercury Iodide - Yellow
The last one may or may not be added, but it may form due to the presence of iodide from the other salts.
More rare salts:
Cerium Iodide-Yellow
Neodymium Iodide - Green
Holmium Iodide - yellow
Erbium Iodide - Pink
Thulium Iodide - Yellow
Gadolinium Iodide - yellow
Ytterbium Iodide - yellow
Which are the most common salts?
The main salts in 4300K bulbs are Scandium Iodide and Sodium Iodide, Dysprosium Iodide is also added to some bulbs. While in higher temperature bulbs, more Indium Iodide is used. This is what gives the salts in those bulbs their red color. It also is really expensive and hazardous to use, which is what gives them their cost.
The exact mixture of salts is unknown, as each company has its own proprietary formula. Trace salts can be added to flesh out the spectrum some, improving CRI.