Hi Sakugenken,
According to
this website, if your car is in the sun for 1 hour or longer, you can basically take the ambient temperature and add 50F to that to find the likely temperature inside your car.
According to the lux
datasheet (page 9), you should be able to operate a Lux at 350mA at an ambient temperature of 50C even if it has some pretty horrible heatsinking properties.
Assuming the LS has a pretty decent thermal path (which it looks like it does) and the Tj-a value is around 40C/W, then you should be able to operate the lux at 350mA if the ambient temp is ~75C (167F). Now that's freaking hot.. But apparently if you have the heatsinkning to do it, it should still keep the Tj lower than 120C.
Now, according to
this from lumileds, a Lux operating at a case temperature of 85C (junction temp 105C) had a loss of ~10% of its light output after 2000 hours (83 days of continuous use). At the same time, a lux at 25C case (45C junction) showed no measurable lumen loss after 4000 hours.
So.. Unless it gets insanely hot where you live (like, over 40C), and you constantly leave the light sitting in the direct sun, then immediately turn it on before it has cooled, then I wouldn't worry too much.
A bit long, but it should be decent data. /ubbthreads/images/graemlins/smile.gif
pb