The "safety lights" / auto-reverse "electric eyes" that I've dealt
with have been very forgiving with respect to alignment.
I just "eye balled" them into alignment until both indicator lights
came back on.
The methods suggested by others will work...eye balling alignment is
quicker & "good enough".
The GDO systems I've worked on have had a red light on each
unit....system is aligned correctly when light on each unit
They are nothing precise like laser safety fence or those red laser nets
crisscrossing the room in some museum with a precious artifact you'd see in an
art heist movie. They use LEDs without any additional collimating optics and
best red LEDs have 30 degree aperture (viewing angle or the cone of most
intensity of light). At 16' distance that translates into a spot 8.5' in
diameter (R = 16' x tan(15) = 4.287' radius). That's a lot of play. As long as
you at least just roughly point it towards the other unit, you can't really miss
across a two-car-garage-wide opening. In other words, if it doesn't work, it may
be because of wiring or other issues, not necessarily alignment.
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