I also changed my trunk light to LEDs. I saw the same dim LEDS upon opening the trunk. If I had to guess this is what i think is going on.
a) Nothing is wrong with the LEDS.
b) Nothing is wrong with your car.
This is ONLY my guess.
Your car has a built in circuit which saves the battery. After a preset time the car automatically shut down power to systems within the car which might accidentally drain the battery. Opening your car doors resets that circuit.
The current needed to power the LEDs is far less than whats needed to power the older bulbs you replaced. The car might be in that battery saver mode upon opening the trunk.
I noticed my trunk LEDs are dim ONLY after the car sits for about 25 mins and I open the trunk first. Once I open the doors the LEDs jump back bright. They stay bright for about 20 to 25 mins.
You are OK