ONLY Comparators light up when a /testfor Command has been activated in a Command block for Entities

ONLY Comparators light up when a /testfor Command has been activated in a Command block for Entities

I put a comparator facing out of a Command block and then set the Scoreboard Objective of an Item 1, but it didn't light up when put on a fast clock. It did set the score to 1 but the comparator did not light up anyway. It only works if you have a /testfor command but not scoreboard...