British light infantry muskets have iron sights, which give a greater chance of accuracy, although there engagments usually took place at 40 yards, but it was also the special methods and drills they used for fighting. The famous light divsion, consisting of the british regiments the 43rd and 52nd along with it portuguese allies, often fighting as the rear guard and vanguard in any engagement. For the most time during big battles, apart from the retreat to corunna, they would fight as a line since it was necessary in most battlefield conditions, often deploying a company to act as skirmishers, but also were able to react faster to battlefield situation, Colborne of the 52nd was given little crediation by wellesley during waterloo, although it was him who dealt the final blow to the french imperial guard, by turning his line without orders, and pouring volleys into the side of the french while advancing on maitlands postion, then proceeding to charge and rout the french army, rolling down there flank. There were many notable light infantry regiments, which often acted as the screen for the main body of the army, pusing back the french piquets, and clearing the way. There are a few battles that were skirmisher/light infantry only battle that happened in the Peninsular War.
http://en.wikipedia.org/wiki/Brown_Bess
check the "New Light Infantry Land Pattern"
I did mention some of the battles here, but the 52nd was just one of the many light infantry regiments.
http://forums.taleworlds.com/index.php/topic,224788.0.html