What happens to a LED with a little more than spec Voltage?

[Undark]

As the title says... I have a P1D CE and an unprotected R123 that gets charged up to 4.2V.
When the P1D CE gets more than a normal 123 cell can give it uses no regulation any more. So what happens, when I use the 4.2V cell with this light?
Will the 4.2 fry my LED? Will the LED get an other tint? Will it become darker? Or will the 0.3V extra be no problem for the LED?
(Cree's specs show max Vf 3.9V)

Can I use it as long as it doesn't get too hot?

TIA!

 

[chevrofreak]

https://www.candlepowerforums.com/threads/147272

As was said in your other nearly identical thread, check out my runtime graphs. It shows that the P1D's will run in regulation on high with an RCR123.

 

[Undark]

Sorry, didn't see the reply because those email-notifications aren't working...

Anyways, thanks for your reply and your graphs... I saw them before but everybody's talking 3.7V RCRs. As mine goes up to 4.2V I still was not sure if the cell will be ok for my light.
Does regulation work above 4V (some webpages say "Max 4V for the P1D CE")?

Thanks, again.

 

[chevrofreak]

The 3.7v or 3.6v claims are the nominal voltage of the cell (after it is about half empty) the same as Ni-MH are considered 1.2v but are actually about 1.45 freshly charged.

Even at a full charge and reading 4.2 volts with no load the voltage will sag quite a bit under the load of the P1D's on high. See the graphs here showing voltage under load. https://www.candlepowerforums.com/threads/117117

The problem with using the 4.2v cells is that you almost entirely lose low mode, and medium can take up to 45 minutes to drop into regulation. The forward voltage of the LED will come into play here. I belive the forward voltage of the Luxeon in the P1D was infact lower than the forward voltage of the XR-E in the P1D CE, which is why there was a short period of higher output with the P1D before it started regulating, and why it took 40+ minutes to start regulating on medium versus the 10 or so of the P1D CE.