Hi, well it's been a long time since I contributed to sci.optics - about 20   
   years I guess.  It's great to see that it's still active.   
      
   A quick question on photometric units - I'm trying to compare the light output   
   from Oleds with that from LEDs.  I'd like to compare total flux emitted by the   
   two sources.  Here's my calculation:   
      
   An LED die has 30 candela output   
   A 1 candela lambertian emits pi lumens into a hemisphere.   
   Therefore the LED emits 30pi lumens   
      
   An OLED emits about 400 nits which is 400 candela/m^2   
   The OLED is 18mm x 7mm , so the OLED emits 400 * 0.018 * 0.007 candela = 0.05   
   candela   
   As above, assuming the OLED is a lambertian emitter   
   OLED emits 0.05*pi lumens.   
      
   So my conclusion here would be that my LED has a flux 600 times that of the   
   OLED.   
      
   My question is about the nit to candela calculation - I've not found any   
   references to this.  It seems sensible, but photometrics are a very strange   
   beast!   
      
   Thanks,   
      
   Simon   
      
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