I think it's because they have a reflector built in to them aswell. You was in need of a change if they were 10 months old. I have seen the same sort of difference on normal t5s that are the same make and spec. It's a real eye opener when you think everything is ok with them until you do this lol. 
		
	
		
		
		
		
		
	
		
		
	
	
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