Hmm, that's not a typical cinema movie projector lamp. The source size is too big. Movie projectors use a small spot source, carbon arc or high pressure discharge. The lamp you have may be from a still image projector or theatrical lamp.
Cool though.
I concur. As I wrote upthread, it's got a P28s socket and is a T/15. Or
FKE as GE would call it. Valve names aren't the only things the Special Relationship between US & UK have disagreed on, it extends to other socketed hollow glass electrics too. The zig-zag pattern of the filament is typical of direct mains powered lights for stage illumination purposes.
An incandescent projector light would typically run on 24 or lower volts, to get a shorter filament and better focussed point source. Like the "ACL" PAR lamps found as landing lights on aircraft; the front undercarriage of the MD80 carries two GE 4596 PAR36 28V 250W lamps, for instance. The 4596 is also used in multiples of 8 as a Very Strong Flood Light, called a "
Molefay"
![](https://i0.wp.com/www.slspro.net/wp-content/uploads/2018/07/8-Lite-Molefay-DWE.jpg?fit=700%2C750&ssl=1)
For cinema, even the new digital variant,
various xenon arc lamps are the norm, with high-voltage igniter and low voltage high current arc source (a contained stick welder, basically). Those bulbs I have respect for, and would not handle outside shipping container without full PPE.
There is enough energy stored in the lamp bulb to send quartz splinters flying several meters across a room.
When the lamp is installed, its safety cover must not be removed until it has been fitted in the lamp housing and shortly before the housing is closed.
...
[The] lamps may only be held with lint-free gloves by the metal bases, never touch the glass with bare fingers! In case the quartz bulb was
touched with bare fingers the fingerprints need to be removed immediately with an alcohol soaked lint-free cloth.
The T/15 is much more harmless. But the "hold by base only" rule still applies. Finger grease is bad. I still am a bit reluctant to touch ordinary valves, having been brought up in stage lighting and being used to those rules.