I am attempting to replace a high-pressure lamp in a 3 LCD (red, green & blue) projector with a 100 W LED array. This resulted in a very disappointing (dim) projected image.

From this stack exchange question / answer it appears most LEDs can produce about 80 lumen per watt. This infers the LED array is producing about 8000 lumen.

Most projectors claim producing between 2000 and 3500 lumen. So even if the projector's red, green & blue filters and LCD shutters attenuated the LED brightness by 50%, enough light should reach the screen to create an acceptable (bright) projected image.

  • 2
    \$\begingroup\$ I think the bigger problem is that the original lamp has a very small emission area whereas the LED array has a much more dispersed area that is not going to be able to be effectively focused by the lens. \$\endgroup\$
    – vir
    Oct 31, 2022 at 18:56
  • \$\begingroup\$ An LCD will attenuate the input light to about 5% of the incoming intensity in addition to the focussing ability of the optical system with the LED source. \$\endgroup\$ Oct 31, 2022 at 19:21
  • \$\begingroup\$ I have to admit, after thinking about it, just having perfect polarizing filters in the light path will attenuate the brightness by 50%. I should edit my question and reduce my assumption to a more reasonable value like 25%. But only 5%? That surprising. Suddenly I see the brightness advantage of a DLP system. \$\endgroup\$
    – st2000
    Oct 31, 2022 at 20:22
  • \$\begingroup\$ The spectral content of a white LED is different than you original bulb. \$\endgroup\$
    – D Duck
    Oct 31, 2022 at 20:24
  • \$\begingroup\$ That is a good point. I didn't think of that. If the dyes in the LED don't match up with the existing Red, Green & Blue filters that would attenuate the brightness even more. Bummer. \$\endgroup\$
    – st2000
    Oct 31, 2022 at 20:30


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