[MF3D.FORUM:138] Re: Light for viewer question

[Tom Hubin <thubin@xxxxxxxxx>]

> >I think that what you are saying is that the far field appears bluish
> >white near the center but maybe yellowish near the perimeter. The near
> >field may have a somewhat different color distribution.
> 
> You are correct, sir.  How are the Nichias?

I have yet to receive the ones that I ordered early December or late
November. At least nobody at the office gave them to me if they were
received. I need to check on that order.
 
> >Imaging the LED so that it ends up at your eye would be much more
> >efficient than using a diffuser. 

> This is excellent.  I would say you want a fairly large spot focussed at
> the eyepoint so that eye placement is not critical.

Actually, the image size depends on the LED size and the lens used to
image it and the eyepiece lens too. Generally the image of the LED will
be smaller than the LED itself. A 5mm diameter LED might be imaged as
somewhere between 3mm and 1mm.

One alternative is to line up several LEDs horizontally. This will
produce an image of a line of LEDs. Location of the eye anywhere on the
line will intercept one or more LEDs. Image brightness will be
proportionate to the number of LEDs imaged into your eye. To me that
means that small images are desirable. This is accomplished by using
LEDs with small viewing angles and a long focal length lens. This will
produce a small image of each LED.

You could wire switches to pairs of LEDs so that the pair you turn on
depends on your IPD. Turn off the ones that miss your eye to save power.
Turn on all LEDs if you are passing around the viewer to several people
and do not want to fool around with switches.

Or you could move LEDs horizontally according to person's IPD. Keep in
mind that the images move in the opposite direction of the objects. The
wider the user's IPD the closer the right and left LEDs should be to
each other.

Adding LEDs vertically is only helpful if the images are small enough
that you can image more than one LED into the eye. That would increase
image intensity. Otherwise, vertical LEDs might be desirable if you find
that hitting a single LED with your eye is tricky.

These are ideas I intend to explore in due time. But I seem to be too
busy designing optics for pay to get much done on my personal optical
projects. So let me know if you are able to use any of these ideas.

Tom Hubin
thubin@xxxxxxxxx