Brightness issues

[Armand Daiguillon]

Hi all,

I was hoping to pick your brains once again.
I’ve been having issues with some of screens looking dim.
So, not knowing if the issue is the bulbs or the projectors I decided to try to find the issue logically.
So first, using a light meter I verified that what was seemingly clear was true – that screens 1 & 4 were brightest. So I decided to use #4 for all the testing. Since it was the brightest, I could rule out the projector as the issue and test the brightness of each bulb from each projector in the same place so I could truly compare bulb to bulb. I have found one issue so far that is preventing me from properly comparing apples to apples.
On this projector #4 if I put a bulb in “Lamp 1” and then get a light reading its one result.
But if I put it in “lamp 2” slot its reading as twice as bright (and looks it too …not a light meter issue)
So my first question is – are lamps 1 and 2 not supposed to be the same light output ? Logically I’d assume they should be the same – but if you look at where the bulb goes into the projector (NEC 900C)
The “aperture” (not right term but from the film ages its seems closest to explain) is not the same. Where the bulb shines into the projector it looks totally different in slot 1 vs slot 2 – and all the projectors are this way. So since the 2 slots are designed differently, I thought perhaps one IS actually brighter by design ?

Anybody have some knowledge on why slot 2 with same bulb shines twice as bright ? And why the two slots aren’t designed the same ?

Any assistance is appreciated. I’m just trying to get everything as good as possible during this downtime.

(below is a pic of where the bulbs go in and how they look different where the bulb shines into projector)


Thanks !!
bulbapp.jpg

[Steve Guttag]

It sounds like a cracked light pipe. I don't recall one lamp being particularly brighter than the other, when new.

[Armand Daiguillon]

It sounds like a cracked light pipe. I don't recall one lamp being particularly brighter than the other, when new.

They had previously not been resetting bulb hours properly - so I dont know the age of most bulbs. I have one new in box that i'm using to set the standard.
With that new bulb though, its twice as bright in slot 2 vs slot #1 - i'll need to see if thats true on another projector.

But the main thing though - any idea why the slot 1 and 2 interfaces are different ?

Thanks !!

[Steve Guttag]

Light pipe != to lamp. The light pipe is what the lamps shine into (what you see when you look in there...you see the end of it). There are two light pipes in a common housing that combine the line from both lamps to output to the fold mirror on its way to the DMDs. If either is cracked, you'll get very poor light.

[Dave Macaulay]

Single lamp xenon projectors have a fairly simple light pipe systrm with an integrator rod, some lenses, and assorted other parts. The twin mercury arc lamp projectors like the NC900 have more complicated integrator/combiner optics. The NC900 has an integrator/combiner rod with two input ports, not two integrator rods going to a combiner. The two input ports are not identical, explaining why the lamp sockets look different. But light efficiency should be close to identical, both ports producing about the same screen brightness from a test lamp.
Have you checked lamp power for each position when you swap the position of your test lamp?
The problem could be from a damaged or miasligned light pipe, damaged lamp socket, problems with lamp power or ballast, maybe something else.
Definitely not normal.
What does NEC support have to say?

[Carsten Kurz]

I currently don't remember - is it at all possible on an NC900 to set brightness for each lamp individually?

[Carsten Kurz]

Armand - do you have a simple Powermeter? You know, one of those 'energy meters' that you can switch between wall socket and equipment? Would be interesting to see if there is a difference in power takeup if you switch lamp position. This is easy to do for an NC900 with it's IEC socket.

- Carsten

[Dave Macaulay]

As far as I recall, you can only select dual lamp, lamp 1, or lamp 2. I think the light output control doesn't operate per lamp setting. I don't know if the setting tries to meet a light level using a sensor, or just sets lamp power. Probably a sensor.
And wow the spell check dictionary in this forum program is awful.

[Carsten Kurz]

I remember I had some notes from an NC900 install I did:

NC900 (legacy/HD-SDI board, so no IMB/IMS):
projector standby: 54W
1 lamp at 90%: 540W
1 lamp at 75%: 460W
2 lamps at 100%: 960W

This is, if important, with the first series of lamp power supplies. NC900 from 2013.

- Carsten

[Armand Daiguillon]

Thank you all for the info. One other question - is it normal for a bulb to lose significant (over 60%) of its brightness over time ?
The manual that comes with the bulbs says to change them out when the projector says you've gone over hours or they might explode (which several have) - but it makes no mention of bulbs also going dim near their end of life. Is such significant brightness reduction normal ? Or is their perhaps something else I need to look into ?


Thanks !

[Carsten Kurz]

It is quite common for them to lose a lot of brightness towards the end. Depends a bit on their usage profile, the software running on the projector (the lamp supplies had some software adjustments over time).

- Carsten

[Marcel Birgelen]

Mercury lamps usually follow a similar curve compared to xenon lamps, they all start to loose considerable brightness at the end of their lifespan. But if you remain within warranty hours, a drop of 60% of effective light output is by far too extreme.

[Miguel Angel Cruz]

As mentioned, the integrator rod may be dirty or damaged , in a service bulletin the following is mentioned:

" The integrator rod moved. If the integrator rod was moved; the image may have low brightness as exampled in the following picture.



The amount of the adhesive to fixed the integrator rod was prescribed was 30mg. However, some units did not have enough amount of the adhesive .The failure does not occurred on all units with the 30mg adhesive.

NDSJ will cover this defective by the warranty until 5 years from production month of projector "

Answering Carsten, it is not possible to adjust the brightness of each lamp individually.

[Randy Stankey]

The manual that comes with the bulbs says to change them out when the projector says you've gone over hours or they might explode (which several have) - but it makes no mention of bulbs also going dim near their end of life.

If you have had several lamp explosions I think you should take a careful look inside those projectors.

Everybody has probably had a lamp explode on them at one time or another. Consider it an occupational hazard. But, "several" explosions means that something is wrong.

First, you've got to ask yourself, "Why?"
Why have you had so many explosions? Are people operating lamps beyond their safe power limits? Are lamps being used past their safe hour limits? Could there be something wrong with the power supply? (Ripple, for example?) If there is anything wrong with the power supply that could, very well, degrade lamp performance, brightness and life span. It can increase the chances of an explosion, too.

Second, after an explosion, it is important to look inside the projector to be sure there isn't any damage.
There is a likelihood of flying glass or metal damaging things or throwing things out of alignment. That could easily make you lose light and the lamp appear too dim.

Others have suggested that you look at the light pipe assemblies and you, yourself, have noticed that something looks amiss inside the projectors. This leads me to suspect that there IS something broken or misaligned inside your projectors and that a lamp explosion had something to do with it.

I suggest that you look inside there and go over everything with a fine-toothed comb.

I bet you a nickel that you'll find something out of whack.

[Marcel Birgelen]

I'm wondering if high pressure mercury lamps are more prone to explosion than xenon lamps are when you drive them past warranty hours. My sample space is far too small to make any educated guess regarding this.

I'd say that due to the smaller size of the explosive part of the average high pressure mercury lamp than that of the average xenon lamp and due to the extra reflector cage that comes with the mercury lamp, an explosion will probably, in most cases, less catastrophic than that of a xenon lamp.

Still, if you had multiple lamps already exploding inside your projector, chances something essential in your light-path got hit and is now causing brightness troubles, are pretty real.