How long should caliper brake springs last?

On Wednesday, July 26, 2017 at 4:40:49 PM UTC-7, sms wrote:
The brakes on my Specialized road bike were not opening all the way when
releasing the brake levers. At first I thought it was the old brake
cables having corrosion so I replace them, and I also put on a set of
new/used levers, since the springs in the original levers were weak, but
this wasn't sufficient.

Went to a bike shop this morning and the shop was closed but the service
area had an open door and I asked the mechanic about replacement
springs. These are for Dia-Compe Edge brakes that came with the bicycle,
circa 1987.

The mechanic told me to just replace the brake set. I ended up buying a
set of Ultegra 6800 calipers from him, with pads, that he had taken off
a bicycle where the owner was upgrading. At first he wanted to sell me
the whole Ultegra group for $300, which had a FC-6703 triple crank, but
he sold me the brakes only, for $50. This is a much better brakeset than
the original, but really I only needed the springs, I was just in a hurry..

How often should I have to replace brake springs. Since this road
bicycle is about 30 years old I figure that the springs do fatigue over
time.

I think this is what I wanted:
http://www.ebay.com/itm/DIA-COMPE-S-...2cda8:g:LiIAAO SwUFtZaPkc

That McDonalds lawsuit established the reasonable temperature that a consumer product can reach without liability. Typically 65 or 68C. That relates to bike lights because most don't control the temperature, yet allow the light to get above 65C. 65C feels hot but you could keep touching without harn if you're a masochist. 68C tells you its too hot to keep touching, but no harm. 70C probably my give a slight scald. One example is the Serfas True xxx series. No temperature regulation, but I've measured 70C on the outside of the metal light head. Other top end lights that do have thermal control, like the Lupines and some L&M lights, regulate to keep the LED temperature lower than what will damage the LEDs, rather than will scald your fingertip.
Only my Oculus lights have a thermal dimmer and automatic temperature control set not to exceed 65C for the hottest spot on the exterior. Then the dimmer reduces power til the temp cools by 4C, then returns to full power.