2) Testing the 430nm bandpass filter

Spectrophotometer instruments typically have a narrow wavelength resolution (approx. 2nm). However LEDs have a much broader wavelength range of 30-40 nm. We decided to try to use a bandpass filter to increase the resolution of the wavelength in the beerometer. We found a 430 nm bandpass filter from Cheshire Opticals, (part # 430.0 IF 10, 1/2" diameter). This filter has a bandwidth of 10 +/- 2 nm, which is a significant improvement over using the LED alone. In initial tests we mounted the filter into the beerometer infront of the LED and measured beer color (SRM) of 14 beers either with or without the bandpass filter. In all cases (except for the Victory Prima Pils), the value obtained for beer color increased when using the bandpass filter.     


Beer
Beer color (SRM) 
without filter
Beer color (SRM) 
with filter
Coors3.13.4
Stella3.63.8
Victory Prima Pils6.76.6
Leffe blonde belgian ale7.58.0
Mongo IPA10.111.1
Two brothers14.418.2
Alaskan raspberry wheat ale15.817.1
Smithwicks imported irish ale15.017.4
Newcastle brown19.025.5
Spaten Dunkel19.628.6
Strand Atticus16.520.4
Alesmith nut brown ale36.548.3
Guinness63.470.6
Craftsman Edgar Ale114.9157.9

 


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