Film-Tech Forum ARCHIVE: Determining Xenon Size

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Posted by Bhaskar Dhungana (Member # 1283) on 10-18-2004, 04:21 AM:

How do you determine size of the bulb for a particular screen? Is there a formula by which you can calculate the bulb size? Also, does throw distance matter in determining bulb sizes.

We have a 33 feet screen and a 44 feet screen, what would be the right xenon size?

Posted by John Pytlak (Member # 331) on 10-18-2004, 10:48 AM:

Much depends on the efficiency of your lamphouse, shutter, lens, and port glass and the gain of your screen. Based on the Strong "Lens Selector and Picture Size Computer", a good "rule of thumb" is approximately 5 watts per square foot of screen area for a matte white (gain=1) screen, two blade shutter, and typical lens and port glass.

The screen area used is the scope image area (2.39:1 aspect ratio), and assumes the preferred moveable side masking for less wide formats.

"Throw" does not usually matter (unless you have to use a less efficient lens for a very long throw). It is the screen image area that matters.

For a 33 x 14 foot matte white screen, at least a 2500 watt lamp would be suggested.

For a 44 x 18.5 foot matte white screen, a 4000 watt lamp would be suggested.

A properly curved gain screen can help reduce power requirements.

Posted by Frank Jerkic (Member # 2446) on 10-18-2004, 08:34 PM:

In my cinema the throw is 60ft, Flat vinyl screen size is 33ft X 15ft on scope and I run a 2000 watt bulb in one of the X60D lamphouse's and a 4000watt in the other X60D lamphouse.
The 2000 watt light is just brilliant but I am not real sure if its because of the larger mirror of the Strong lamphouse
Cao
Frank

[Roll Eyes]