daytime running lights

DRLs in general are either not available or are a factory option in the USA... Except GM Vehicles which put them as a standard feature on all their new cars.

In many of the provinces in Canada, including Ontario, they are required by law. I'm not sure which provinces do not require them but I think Quebec is one of them.

Specifically in Ontario, Daytime Running Lamps were required by the Highway Traffic Act when it was amended in 1992. These lights had to be visible from 150 metres away. Daytime Running Tailights were considered, but after many tests, they found people could not tell the difference between the DRTs and Brake Lights, so that project was scrapped (that is also another reason why it's not smart to drive with your headlights on during the day, the difference in contrast between tail and brake lights is not great enough for some people to notice the change).

Woo Hoo!!! I can use my chemistry 101 knowledge!

HIDs are produced by a process called High Intensity Discharge, aka electron excitement. Basically, there is no filiment in an HID bulb. Just a tube of gas with an electrode at each end. Inside the tube is Xenon Gas (also used for street lights, camera flashes etc.) The electrodes send a current through the gas. The gas absorbes the energy and excites the electrons in the gas to the point where they can't take any more. At this point the atoms of the gas can't take anymore energy, so they release it in the form of light. Every gas has a different "activation energy" (energy it takes to excite the gas enough to produce light). If there isn't enough energy, no light is produced, and if there is too much, the excess energy gets turned into heat. So that explains why they can't be dimmed. You can make HIDs out of any gas, but Xenon was selected since it produces a light with a spectrum closest to daylight. (example of HID lights with other gasses are Neon Signs).

In response to the second part of why HIDs cannot be used for DRLs. The answer is, they can. Mercedes-Benz has been using their HIDs as their DRLs for years in Canada. The problem is cost. HIDs bulbs (as you know from all the conversion kits) are far more expensive than regular light bulbs. Granted they do last longer though. Mazda probably elected not to have the HID as the DRLs because with the HIDs always on, the bulb's life would be shortened, and they would have to replace HID bulbs instead of normal ones. I guess M-B figures, if you can afford a Mercedes, you can afford the replacement bulb. Why Mazda didn't make the DRLs the high beam and give HIDs to the Canadian buyers is beyond me.

I know that's a lot of reading, but I hope that helps.

P.S. Now you can guess where my nickname came from... I used to be obsessed with these kewl bulbs. Yes, I am a nerd.