I am trying to understand which LED is brighter and why

I have one and the datasheet shows an LED 585nm 3KR , 583nm, 10mcd, 120 DEGREES

The second LED datasheet shows LED SMD 1206 CL-YL 180m 60D 3K SURFACE MOUNT LED, 1206, CLEAR YELLOW 595nm, 180mcd, 60 DEGREES

My understanding is the higher the mcd value the brighter the LED is that correct. I am getting so much mixed information I am lost.

 

Yes MCD (Millicandella) -- denotes brightness. The degrees is the viewing angle. How far the light spreads.

 

Note that you can quote a very high mcd value if you use a lens to focus a narrow beam. This makes it hard to compare values when the dispersions angles are different.

 

Convert the millicandelas and angle to lumens for each LED to compare.

http://led.linear1.org/lumen.wiz