Xenon short-arc lamp: Difference between revisions

Whenever you put in a new xenon lamp it must be properly aligned on the X, Y and Z axis (horizontal, vertical, axial) to have even illumination and achieve the proper luminance on screen. Poor lamp alignment can result in hot spots of light on screen, damage the reflector, lens, and even the print. A lamp alignment should be performed when a new lamp is installed and periodically thereafter because the position may drift over time.

Lamp alignment should be done whenever a new lamp is installed, if you see hot spots or shadows on screen, film prints exhibiting embossing or burns, or if you are switching between different film gauges on the same projector.  

 

During alignment you will see the following on screen: The shadow of the anode assembly at the end of the lamp is the dark circle, immediately ringed by visible plasma (the electron arc). Surrounding it is the circle of light collected by the reflector, and reflected upon the screen. This area comprises most of what we see, and should appear bright white and essentially even in luminance upon completion of the alignment.

Always have lamphouse dowser closed before striking a lamp -- striking a lamp when the motor is off and the dowser open can result in melted shutter blades, changeover plates, melted film, or cracked lenses.  

2. Remove lens (Kinoton users should remove gate runners so they aren’t damaged by the heat). Turn on lamp. Start motor and open dowser.

3. Make the axial adjustment, (or the “focus”) till you see a circle with a little bit of plasma around the edges of the anode shadow (people call this “the eye”).

5. Re-adjust the axial to bring the plasma back in, until you have a tight symmetrical circle free of light (plasma) fluttering around the anode shadow.

6. Put in a lens (cinemascope is best as you want full aperture). After you put the lens back in: look for even illumination across the screen. With the lens in, the shadows will be gone and there will be a hotspot in the center of the screen. Focus the lamp (making fine X and Y axis adjustments as necessary) until no shadows are visible at the corners and the illumination is even across the screen. You want it bright, flat and centered with no hot spots! Changeover from projector 1 to projector 2, you want them to look as similar as possible.  

7. You may want to fine-tune the bulb focus with the lens in place until you have even illumination, then take the lens out again to check the symmetry of the anode shadow.  

The [[Society of Motion Picture and Television Engineers|SMPTE]] specification is 16fL ([https://en.wikipedia.org/wiki/Foot-lambert foot lamberts]) with uniform illumination across the projected area without film in the projector (open gate). Because spherical widescreen formats (1.66:1, 1.85:1) are the least light efficient, and 1.37:1 and Scope are more light efficient, you can split the difference with 15fL for [[Aspect ratios|1.85:1]] and 17fL for [[Aspect ratios|Cinemascope]].

If you’re checking luminance through the port glass with your meter subtract 1~2fL. It’s always best to take your final readings in the auditorium itself.

* If dark spots appear in the area within the circle of light (with the lens removed), the reflector should be inspected for pitting, explosion damage, or any other damage to the reflective coating.  

In practice, their packaging is secure enough that it can be very difficult to destroy the lamp in this fashion.

[[Lamphouses]]

[[Carbon Arc lamp]]

[[Light sources]]