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Hey guys, I have a couple LED vs voltage questions. I've tried goggling the answer but I just don't understand electronics

Can I run a 3MM red (V): 2.0-2.2,(MA): 20 LED on a CR2032 3V, 200mAH battery with out a restrictor?

Can I run 2 of the same LED on the same battery with out a restrictor?

I've built 2 Daemon princes and 2 Greater demons so far with out any issues so far. Just want to make sure that my LEDs don't burn out.

Could you? Largely - yes. Would I? Probably - no.

The internal resistance on the coin batteries is actually high enough that they don't need a limiting resistor. That is why they are my power supply of choice for LED systems (that and they are smaller by a long shot than other options like AA and even AAA battery packs.

The issue though is the voltage. While you can run a 2v LED on a 3V supply, and the light will work just fine, it will reduce the effective life span of the LED. Granted, we are talking about dropping it from something silly like 15,000 hours to maybe 12,000 hours.

Over driving LEDs on the voltage side doesn't impact them as much as overdriving them on the current side of the equation (you can actually get them to pop if you push enough current through them). Granted, do to the way electricity works, increasing the voltage does generally increase current as well...though it doesn't always have to be that way (just with battery based power supplies it normally is).

Anywho - I just go ahead and simplify things and use 3 v LEDs instead. You can get them in the same sizes, they are just doped in order to have optimal operation at 3 v instead of a higher or lower voltage.

For most hobbyists, achieving the ideal lifespan isn't that important. Unlike something like - say - a power indicator on a piece of electronic equipment which may run 24/7 for 10 years...most of our toys run for a few hours a day once a week. Even overdriving an LED at the high side of their limits will still provide you with more than enough lifespan to not have to replace them until there is a new technology that replaces them.

So should I install a limiting resistor on the ones I've already built?

What about running 2 of my LEDs on one battery?

You can run multiple LEDs using one battery. Just connect them in parallel way.
(Anode to + and katode to - on both LEDs)
Voltage is same in every LED, and current divides to each, so if one works well, multiple will too.

I run 6 (2,2V) LEDs on AA batteries (3V) on my Land Raider. It shines third week in a row, without any problem. (just insensity decreased, as batteries are being drained)

If you really want to, you can install a potentiometer (adjustable resistor). You can adjust resistivity using screwdriver, and achieve ideal shine level. Also you get rid of calculations.
But I don't really find it necessary.