Hi Steve, 
You are certainly getting a hell of a lot of light - much more than on the article I posted above. Are you overdriving it? You are getting more light than Mike Kirda measured with 2x400w Ushio bulbs.  
 
Your readings at 6" are similar to calculated ocean values at 5 - 8 m depth near the equator, and your 24" readings are in the range of 9-15 m. Pretty decent. 
 
My 24" readings are less than the light at 20 m. 
 
The meter is a Quantum QMSS. 
		
	
		
		
		
		
		
	
		
		
	
	
	 |