OT: How to compare LED lamp and discharge lamp video projectors?

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There isn't one nor can there really be one. The biggest part of the issue is that the spectrum of each lamp type is different. The Lux to Lumens conversion requires specific assumptions about the spectral intensity curves. No real lamps meet these requirements. See Color Rendereing Index (CRI) as well.

That said, lumens rating gives a reasonable approximation of how much humanly perceived illumination can be expected for any lamp.

BTW decent arc lamps can be focused pretty well, it is not all that extended of a light source. For ugly try line filament incandescent lamps; of course when you want a line of illumination (photocopiers) they may be nearly indispensable.

YMMV

?-)

There isn't one nor can there really be one. The biggest part of the issue is that the spectrum of each lamp type is different. The Lux to Lumens conversion requires specific assumptions about the spectral intensity curves. No real lamps meet these requirements. See Color Rendereing Index (CRI) as well.

That said, lumens rating gives a reasonable approximation of how much humanly perceived illumination can be expected for any lamp.

BTW decent arc lamps can be focused pretty well, it is not all that extended of a light source. For ugly try line filament incandescent lamps; of course when you want a line of illumination (photocopiers) they may be nearly indispensable.

YMMV

?-)

Someone demonstrated to me a Philips PPX2480 in an industrial discharge-lamp floodlit sales barn . On battery so 55W , not the mains 80 W lumens, but at about 7 foot diagonal so probably about the same as 80W on 10 foot diagonal , stated max in the specs. But would be totally inadequate. In a darkened room it would be fine but the operational requirement here is for use in a daylit, but indirect sun, room with some , non-blackout, curtains drawn if necessary or room lighting sufficient to read printed paper. So looks like 300W (LED lumens rating) at least for my purposes for 10 foot diagonal. Still don't know what that equates to in discharge-lamp projector Lumens

The current projector was rated 1700 lumens, 200W, but is probably reduced output these days , but still useable in those room lighting conditions at 8 to 10 foot diagonal

I see Philips components, Plymouth UK, this year is producing 80 lumen per watt LEDs and next year 150L/W