Re: Brightness of viewers

[P3D Dr. George A. Themelis <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Dear Paul,

Thank you for your excellent report on viewer brightness... 
This is one of my favorite topics and you fed me with good food!
Just a few points to add to your reported data:

- In my halogen bulb flier, I give graphs that show illumination (measured
  by EV, as you did) as a function of voltage for 4 different bulbs: 
  Bright Halogen (800 mA), dimmer halogen (500 mA), No. 245 (500 mA) and
  No. 14 (300 mA)

- The brightest bulb is the clear halogen bulb, which is 1 f-stop (or 1 EV)
  brighter than the No. 245, at any voltage.  The frosted bulb is 1/2 
  dimmer than the clear bulb since the frosted envelope increases light 
  diffusion but reduces intensity.

- Plain tungsten bulbs get darker with time while halogen bulbs do not.

- When comparing brightness, the temperature of the source is also a factor.  
  Experience shows that a bulb that emits "whiter" light appears to the eye 
  brighter than a bulb that emits "warmer" light, even though both register 
  the same EV value.  So, caution when comparing the "white" halogen with
  60W household or 110 V (in Kodaslide, etc.) bulbs.

- Eye adaptation is important.  The same viewer (illumination level) might
  appear excessive to the dark-adapted eye, but dim to the eye in a 
  brightly lit environment.

- In addition to sheer intensity, distribution of light is also important
  in a viewer.  Good illumination means uniform illumination.  Non DrT
  viewers have the tendency to cast shadows at the edges, which can be
  distracting.

- In addition to light bulbs, viewer components that affect illumination 
  intensity and distribution, include the reflector, geometry and nature
  of bulb compartment.
 
The above concern viewing slides in a viewer.  As we discussed earlier, 
illumination is very important when viewing anaglyphs, and also prints in 
a print viewer.  Even & bright illumination without shadows or reflections 
is the aim under any kind of stereo image viewing.

-- George Themelis


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