Mike is going to have something to say .... 
Hey I don't think the questions your asking are dumb as I had similar ones, I think that grumpy dude is trying to point out unless the power supply is constant current the LED will draw its max current (which can change with the environment) and last not as long, so you don't need the resistor for the PWM signal, you need it to limit the current into the LED to slightly below what it wants to ensure long life.
But yeah I think in the real world LEDs are cheap and if it works and last long enough for you then its working in my book and worse products have been brought to market lol
That's a ridiculously short-sighted point of view, for anything other than messing around in the sandpit.
The leds the op is using are not that cheap- not compared to normal ones that we all buy by the handful anyway. But that's not the point- the real cost is perhaps a failure of other parts of a project where a signal led may not come on to alert the user to a problem because it had burned out. Not to mention the cost of dismantling plant to get at the burned out led and replace something that could have been spec'ed properly in the first place.
Fully agreed! In any case, these LEDs cost 2€, so even if one burns out, it is not a big loss, as this is not a critical application. I believe that with the PWM solution they should be pretty safe, though - with voltage capping through buck converter, current will be constant, and slightly below the rated value.
Not sure I understand as the resistor before the mosfet is limiting the current right? where you want to be using the dc voltage to tune the current going through the mosfet right? Anyway like I was saying if your testing it and its working for you its probably going to be good enough haha
Edit: ah just realised your saying you have switched to a buck converter.
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