Visor differences - black, iridium, mirrored?? 
  Looking to get some visors for my helmet but apart from looking cool, are there any differences between visor coatings?  
 
 I guess black is just darker but are the mirror and iridium versions just a coating or do they work differently and filter out more/less of the sunlight.  Are they generally lighter than the black versions.  Also what are the best ones for poor visibility - in snowboarding googles - yellow / orange were the best.
 
 I have a variety for my AGV already but have changed my helmet brand so looking to get new ones so interested in the differences.
 
 Thanks all
 
 simon