My questions: How to measure/compare the lighting output of led lights? Is there a way to convert these numbers? All I want to know how much light these lights output so I can compare them.
You can try this calculator
I haven't tested whether it's absolutely correct, but that is basically the input needed for a conversion. Lumen
is a total flux of light (in all directions, or concentrated by a reflector), Lux
is the amount of light a given surface area receives or emits (usually expressed per square metre, if you want to avoid angles and distance).
One Lux is one Lumen per square meter, but for conversion you would need to know how the flux in Lumen is spread and the distance at which it is measured.
Watts only tell something about the power consumption, nothing about how efficient that power is transformed into visible light (and e.g. heat).
are some more calculators.