Dimmers for different Bulb types

These 2 dimmers look the same but are completely different.

Right side: Incandescent(regular light bulbs) only
Left side: LED and CFL compatible

How do you tell the difference?
It is written on the dimmers....

Magnetic ballasts: Use ONLY dimming ballasts shown on chart

in step 2 of Pre-Installation. Do not mix 1 and 2 lamp ballasts in

any one dimmer circuit. Do not mix ballasts manufactured by more

than one company. Using single lamp ballasts will produce the

most consistent low end dimming level.

Skylark Contour® C•L ® Dimmer
 Dimmer for CFL, LED, Halogen, and
Incandescent dimmable bulbs.