So I'm spending time researching different parts of the IS and recently I've started researching the stock HID's.

For those who don't know: Currently, D4 bulbs are the latest in HID technology. D4 and D2 and generically the same technology, however, D4 bulbs are mercury free, thus are more environmentally friendly. Previous HID bulbs have mercury and in the case of a frontal accident the bulbs may shatter, thus releasing mercury into the open. Also D4 bulbs run at 35W @ 42V and D2's run at 35W @ 85V.

D4 bulbs currently have 3 forms: D4R, D4S and D4C. Similarly to D2 bulbs featuring D2R, D2S and D2C. The R represents bulbs designed for reflector housings, S for projector housings and C for both housings. R type bulbs have a small ceramic layer on the bulb to prevent the light from reflecting off the housing reflectors upward, thus removing glare. You can see this happening in Toyota Prius models. S type bulbs do not have the ceramic layer as projectors can focus light better, thus having little to no glare and thus utilizing "more light". Now this is where I'm lost on my research.

Obviously all D4 bulbs fit eachother, it's just the glare problem. If that's the case what is a D4C bulb? They will fit the housing indefinately but if they don't have the ceramic layer, wouldn't it be better just to call it a D4S bulb? And if they do have the layer, then we can call it a D4R bulb. Does anyone have anymore information on this?