Light efficiency in stereoscopic projection

[Update : Barco has updated their page with a single PDF. This broke the images below]


Two LCD projectors –
Barco has a really interesting page about how much luminosity you can get from your stereoscopic projection system. I’m duplicating it here just in case they decide to get rid of it one day, but for a possibly more up to date version, see the original page.

Light efficiency

Stereo lumens

With stereo projection, light output is at least halved in the process of creating a separate left and right eye picture. Active or passive stereo have a different impact on the remaining brightness. Projectors of different technologies with the same ANSI lumen specs will give quite different STEREO lumen results. STEREO lumen is the only practical value for measuring brightness in Virtual Reality applications.

The influence of the screen has not been taken into account in the pictures. Indicative average values depend on used materials. yellow = polarized light

Active stereo

Single CRT or DLP™ projector

As the projector sequentially projects the left and right eye images, the duty cycle would be 50%. However, the extra blanking between the left and the right image that is required to ensure a good stereo separation further diminishes the light output, resulting in an efficiency of about 45%.

Due to polarizing, each eye receives less than half of the light left. As shutter glasses do not open and close instantaneously, and due to thelight lost from the polarization, efficiency of the active stereo eyewear is rated at about 35%. The overall efficiency of the active stereo process is thus 45% x 35% or approximately 16%.

Passive stereo

Two CRT or DLP™ projectors, Polarization

The unpolarized light coming from the projector is externally polarized, which diminishes the brightness by more than half and reduces the efficiency to about 45%. Then the polarized image is viewed through passive stereo glasses that transmit the polarized light at 84% efficiency, resulting in a final afficiency rate of approximately 38%.
Two LCD or DLP™ projectors, Infitec™

Using the Infitec™ technology, the white light from each projector is passed through a color filter that divides the primary color bands into two separated regions (more information > go to Infitec™ stereo seperation). As the total spectrum needs to be split into two separated complimentary parts, a maximum theoretical efficiency of 45% is obtained after Infitec optimization. Keeping practical implementation and color optimization into account, 30% efficiency is achieved after Infitec optimization. The two Infitec-optimized images are viewed through the matching filter, with some associated reflection and absorption loss, so the final efficiency rate is about 27%.

Single projector with Z-screen

When a ZScreen is used to polarize the light, a single projector is driven in active stereo mode. As a ZScreen is even slower than active glasses more blanking is needed between left and right signal, resulting in a duty cycle efficiency of about 40%. Next the light is polarized where 50% of the light is lost. The ZScreen polarizer sheets transmit unpolarized light with an efficiency of about 35%. With the passive stereo eyewear also having an efficiency rating of 84%, the final efficiency rate is about 12%.

Two LCD projectors

LCD panels polarize the light that passes through them in different directions. Through internal polarization Barco is able to maintain about 70% of the original light output.
Cumulated with the 84% efficiency of the passive stereo eyewear an overall projection efficiency of 59% is reached.

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