How would the Bat Signal really work?

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sonofaresiii

Well-known member
Every time I see the Bat Signal depicted in movies or comics, all I can think is "No way would a source that big make that clean of a shadow from a pattern that close to the source." I can't see any way the light doesn't either just completely wrap around the bat-symbol, or the bat-symbol blocks the light completely (depending on the size of the pattern). I figure maybe they can put a donut in there to cut down on the stray rays from the can, but isn't that just really changing the size, which means it wouldn't project all the way to the clouds of Gotham? Or they could potentially extend the glass/pattern out, flare it so it's bigger than the source? (which is the same idea)

So what do you guys think? What are the specs of a spotlight that projects a bat symbol on the clouds over Gotham? And how bright would it need to be to still be seen (even if not projected) into the air for Batman to know he's needed?
 
The basis for the bat signal is the old Hollywood spotlights that were used for movie premieres. Those spotlights had a point source of light (carbon arc) and a concave mirror. This is exactly the same principle as telescopes, but in reverse. So the bat signal would simply put a cutout over the spot light and yes, a clean outline would be projected on the clouds above. No clouds, no signal.

Look at how focused that beam is:

https://www.pinterest.com/pin/66920744436247079/
 
No. An HMI spotlight is not a true spotlight. It is typically a Fresnel spotlight, which is a bit misleading as it does not send out a focused beam. Also, they don't have nearly the light output that the old spotlights did. These things were monsters, built simply to put a big beam of light in the sky.

[edit] Come to think of it, they were probably invented to spot enemy planes. http://www.skylighters.org/howalightworks/


This one is for sale - only $12,000.
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Lighting up a low cloud would be easy enough - that's what anti-aircraft spotlights have always done - but getting a nice hard-edged bat symbol would be much harder, due to gradual dispersal of the beam. The obvious modern solution would be lasers, but that wouldn't give the classic bat signal look...
 
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