Playing a movie with dim visuals

[Jerry Bian]

hi all：

I have a Barco DP2k-20c with dim playback. I learned that it has 18500lm.
Can someone tell me how to calculate the required luminous flux based on the screen size?
Thank you very much

Jerry Bian

[Steve Guttag]

It has the potential for 18,500lm. That would be with a new reflector and optics and a new lamp and with the most optimal lens (and they never tell you which one they rated the projector with and what zoom position it was in.

As for calculating lumens needed, it is square area multiplied by desired light level, presuming a matte-white screen. So, lets say your screen is 20 x 47.8 feet (2.39:1 ratio). To light up the scope image, on a matte-white screen, you'd multiply the width x width/1.8963 x 14fL = 16,869lm. But you need to allow for the port hole (between 2 and 10%, typically...if new and clean), Color Correction 5% and, xenon aging (unless you plan to put a lamp in every show)...better allow for 25-30%. Factoring all of that in, you'll need closer to 25,000lm...on a new projector. I've see as much as 30% of the light go away on the internal dirty optics (reflector, cold mirror, fold mirror, light pipe/lenses and even the prism.

[Stefan Scholz]

Projector manufacturers name their projector models according to the initial maximum light level, with a high brightness (bad image) lens. As Steve pointed out, unknown lens type, etc.
Xenon bulbs age significantly over time, within the first 20% of the rated lifespan, they loose 30% power. Going to 50% at rated life (Data found at Ushio)
Projector guts also loose efficiency, lamp reflector surfaces burn off, optical surface get matt, even the micro mirror devices loose reflectivity, so it would not be uncommon to have a projector with dim light.
I recently saw an NEC 1200. It was set up against a wall at 12 ft wide image. Lamp setting of the 2.000 W bulb (around 1.000h) at 99%. There was literally NO light on the white wall.
I tried to adjust focus, impossible. Going towards the scree, we could focus the flyscreen covered by a wide halo.
Looking on the usage counters... 58.000 hours since 2012, and this was used in an operating theatre until a few weeks ago.
As I know, the light modulating units were rated for 20.000 hrs.

[Jerry Bian]

It has the potential for 18,500lm. That would be with a new reflector and optics and a new lamp and with the most optimal lens (and they never tell you which one they rated the projector with and what zoom position it was in.

As for calculating lumens needed, it is square area multiplied by desired light level, presuming a matte-white screen. So, lets say your screen is 20 x 47.8 feet (2.39:1 ratio). To light up the scope image, on a matte-white screen, you'd multiply the width x width/1.8963 x 14fL = 16,869lm. But you need to allow for the port hole (between 2 and 10%, typically...if new and clean), Color Correction 5% and, xenon aging (unless you plan to put a lamp in every show)...better allow for 25-30%. Factoring all of that in, you'll need closer to 25,000lm...on a new projector. I've see as much as 30% of the light go away on the internal dirty optics (reflector, cold mirror, fold mirror, light pipe/lenses and even the prism.

hi Steve：
The screen gain I am using is 2.4. Is 16869lm x2.4 the ideal brightness value.

[Steve Guttag]

Negative...it is a popular misconception that screen gain allows for lower lumens...quite the opposite. While you'll get the desired lumen in the very center of the picture...everywhere else will be dark.

[Jerry Bian]

Negative...it is a popular misconception that screen gain allows for lower lumens...quite the opposite. While you'll get the desired lumen in the very center of the picture...everywhere else will be dark.

The Luxe screen solves this problem very well.At present, it is suspected that the selection of the projector model is too small, resulting in a dim image with insufficient lm.

[Mark Gulbrandsen]

I recently saw an NEC 1200. It was set up against a wall at 12 ft wide image. Lamp setting of the 2.000 W bulb (around 1.000h) at 99%. There was literally NO light on the white wall.
I tried to adjust focus, impossible. Going towards the scree, we could focus the flyscreen covered by a wide halo.
Looking on the usage counters... 58.000 hours since 2012, and this was used in an operating theatre until a few weeks ago.
As I know, the light modulating units were rated for 20.000 hrs.

I installed quite a few NC-1200's and never heard this sort of a problem until I read this post... I've even had NEC's in areas where the air is not so good, especially the winter air, because everyone is using their fire places all winter long. Sounds more like a failure of something like the integrator, or a relay / heat mirror in the optical system. I also never heard that the light engines were rated for 20,000 hours... that was never mentioned at the several NEC training classes I attended. Perhaps they ran the projector without the filters for a long time. When I retired many of the NEC's I installed were at well over 50k hours. I've had an NC-900 that needed prism cleaning, but instead of paying Strong's rediculous price, it was cheaper to just get a demo NC-900 from the other distributor. If you do repair it, I'd be curious to know what the problem was... They have been very reliable projectors overall.

[Steve Guttag]

The Luxe screen solves this problem very well.At present, it is suspected that the selection of the projector model is too small, resulting in a dim image with insufficient lm.

Apparently not. You are the one complaining of the dim picture. You are not going to get a high gain screen to have an even distribution of light and if you set the center to be at 14fL, you'll never meet SMPTE specs (431-1) on the sides unless you curve it (sufficiently). Do you really think the screen is going to, somehow, alter the physics of light?

Measure the light from the center seat in the auditorium/room. Measure, at least 9 points on the screen with the edges being just 10% or so in and post what you read. Or, better yet, get ahold of a USL PSA200 meter and post its 45-position light reading.

What are the particulars of your theatre? That is, what is the actual screen size and the "Flat" and "Scope" image sizes and what, if any, screen curvature (radius, presuming cylindrical horizontal curve)?

[Marco Giustini]

Jerry, as Steve rightly points out, it's the law of physics. High gain screens act like mirrors by focussing the light to a narrower angle instead of diffusing it at 180 degrees.

A picture speaks a 1000 words though. Here is a silver screen with a matte screen in front of it. YES, on the hotspot the silver screen is brighter. But which screen will deliver a better picture in your opinion??

silver2.jpg

silver1.jpg

[Jerry Bian]

Apparently not. You are the one complaining of the dim picture. You are not going to get a high gain screen to have an even distribution of light and if you set the center to be at 14fL, you'll never meet SMPTE specs (431-1) on the sides unless you curve it (sufficiently). Do you really think the screen is going to, somehow, alter the physics of light?

Measure the light from the center seat in the auditorium/room. Measure, at least 9 points on the screen with the edges being just 10% or so in and post what you read. Or, better yet, get ahold of a USL PSA200 meter and post its 45-position light reading.

What are the particulars of your theatre? That is, what is the actual screen size and the "Flat" and "Scope" image sizes and what, if any, screen curvature (radius, presuming cylindrical horizontal curve)?

hi Steve
49.21x20.57(2.39:1 ratio).2048x858 scope
screen curvature (radius, presuming cylindrical horizontal）I'm not very good at this.

[Steve Guttag]

That could work with the DP2K-20C. I would bump up my 2D light levels to 22fL on Flat and about 19fL on Scope. But this all depends on the actual condition of your equipment (how dirty is the optical path?). Probably more like 7fL on Flat for 3D and 5ish for Scope 3D...unless you want to just throw lamps at the 3D Scope every few hundred hours.

I do think that projector is a bit small for that sized screen. With a Matte White screen, I'd go with, at least a DPxK-23B, from the Barco line up. So, the same lamp size but with a more efficient optical system. For laser stuff, I'd go with the SP4K-25 or brighter...again, with a matte-white screen. I recently did a 50-footer and used the SP4K-35 with a high-contrast lens on a 1.3 gain screen. It came out real well. If you have to keep silver, you can skate by on the 20 but light uniformity on silver always is rough. Curving can help on lateral uniformity but hurts on geometric uniformity.

[Jerry Bian]

It has the potential for 18,500lm. That would be with a new reflector and optics and a new lamp and with the most optimal lens (and they never tell you which one they rated the projector with and what zoom position it was in.

As for calculating lumens needed, it is square area multiplied by desired light level, presuming a matte-white screen. So, lets say your screen is 20 x 47.8 feet (2.39:1 ratio). To light up the scope image, on a matte-white screen, you'd multiply the width x width/1.8963 x 14fL = 16,869lm. But you need to allow for the port hole (between 2 and 10%, typically...if new and clean), Color Correction 5% and, xenon aging (unless you plan to put a lamp in every show)...better allow for 25-30%. Factoring all of that in, you'll need closer to 25,000lm...on a new projector. I've see as much as 30% of the light go away on the internal dirty optics (reflector, cold mirror, fold mirror, light pipe/lenses and even the prism.

steve.width x width? width x height？1.8963 How to understand？sorry I don't really understand.