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Topic: When is a lamp too bright?

Alan Rik
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From: New York City, NY, USA
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posted January 11, 2004 02:03 PM

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One gentlemen had told me once in regards to projector light that he had a throw of about 20 ft and a picture of 6-7 feet wide. He owned a Bauer T610, and said it was the greatest projector he had ever owned. I asked him about the brightness issue and if he felt that the 150watt lamp was bright enough. He told me he puts in on the low setting because the bright is TOO bright!
So what do you think - When is bright TOO bright? And what is your throw and image size? I have always felt that the brighter the light the better the picture-

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Alan Gouger
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posted January 11, 2004 02:15 PM

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Alan

I find myself wanting more light output from my projectors including the Xenon regardless of screen size.

I have a Bauer T610 and there is no way I feel it could give a comfortable image at 7 feet wide without the need for some high gain screen material. Nice projector though with great sound.

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John Whittle
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posted January 11, 2004 02:36 PM

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Well there is an SMPTE standard for screen brightness (actually it's projector brightness). It's 16 Fl (that's foot lamberts, not foot candles). The reason for that measurement is because it is measured at the screen, it is the light falling on the screen and thus doesn't take in screen gain. It also takes into account the shutter, the projection light source, projection lens. It's a measurement made without film in the gate.

The problem with measuring lux is that it's the light from the lamp without taking into account the lens or the throw. It's useful in comparing projectors but not projection set-ups.

As for "too bright", it seems a bit out of line because very few theatres actaully get 16 Fl on the screen, it was a measurement that the projectionist would routinely make before we ran either a 35mm or 16mm answerprint in the laboratory screening room.

BTW would someone explain the "corned beef" joke?

John

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Kevin Faulkner
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posted January 11, 2004 06:55 PM

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Never is my answer to that question. We want as much as we can get through that small super 8 frame without damage to the film that is.

Corned Beef joke? well I think Tony should enlighten everyone on that. [Wink]

[Wink]

Kev.

--------------------
GS1200 Xenon with Elmo 1.0...great combo along with a 16-CL Xenon for that super bright white light.

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John Whittle
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posted January 11, 2004 07:55 PM

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You bring up a good point that is often overlooked. The size of the aperture is a limiting factor in how much light can be put on the screen. Hence you can put a bigger lamp behind a 35mm frame than a 16mm frame and a much larger lamp behind a 70mm frame or Imax frame. Aside from the heat (drive-ins used to have water cooled gates) the aperture provides an f/stop of it's own.

It is also possible to put more light through a color print than a black and white print since the silver in the black and white print absorbs the heat and becomes a limiting factor.

In the "olden days" some film exchanges would get back black and white prints from drive-ins that were warped from the heat could no longer be projected and hold focus.

John

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Mal Brake
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posted January 12, 2004 04:36 AM

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Hi Kev,
with regard to your comment about heat damage to the 8mm frame, could I ask you how effective is the split glass heat absorber on the ST 1200 HD?
By the way I took your advice and ditched the 250w lamp from the GS.
Mal

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Ugo Grassi
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posted January 12, 2004 04:46 AM

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Into a cinema manual book I have, there are some rules. The right light on the screen is 11-14 footcandle (or foot lambert? I'm not sure);
1 footcandle=11 lux about (I hope to right remember)
I remember too: 1 FL=1FC. Is it right John?

Anyway you have to obtain about 120-150 lux.
Example: My GS1200 HTI gives 1000 lux on 1 metre screen. This power is enough until 3 metres screen:
1000/9=111 (a little bit less)
An Elmo two blades shutter gives 410 lux. On two metres screen:
410/4=102

[ January 12, 2004, 06:48 AM: Message edited by: Ugo Grassi ]

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Ugo

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Alan Rik
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posted January 12, 2004 11:30 AM

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Then according to your measurements, a GS1200 xenon not HTI which I believe has a lumens of about 510, would be underlit for a picture of 10 feet wide. Are you sure? That would mean with your HTI GS the perfect light amount would be a picture about 8 feet wide only. That seems very small for what the HTI light source was intended. Auditorium use for the GS I assumed would be the intended use and it would seem that a picture much larger should be expected.

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Ugo Grassi
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posted January 12, 2004 12:26 PM

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Right question! My friends and I spent a lot of time to talk about this problem! This is the theorical answer to the question, but probably the practical is a little bit different.
We was in a cinema to see a movie projected by a Fumeo 9145 (it has a XBO 500 watts Xenon lamp). This machine gives about the same lux of my Elmo HTI. The screen was of 3,70 metres. At the end of the projection we measured the lux (one of my friends, Gianni, is a photography director in RAI, so he has the exposimeter always with him!): on the screen 75 lux!!! But the image was good during the projection.
We think it's possible - with a discharge lamp, with an halogen the "impact" to the eyes is different - to project with less light than the standard rules; but Gianni thinks the image will not respect the right equilibrium light-shadow.
So, if the scene is shot at the sunset, on the screen the scene will appear like later played.

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Ugo

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Alan Gouger
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posted January 12, 2004 12:55 PM

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Ugo

Can the HTI bulb run off the GS1200 power supply.

I bought the complete kit including power supply from Whitners (sorry for the misspelling) but Im not sure if I want to install it in my Fumeo or Xenon GS. The Fumeo is better for this as its all metal parts.
The HTI is "much" brighter than the xenon in the GS. I want to avoid having to use a stand alone power supply if possible.

Thanks Ugo.

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Kevin Faulkner
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posted January 12, 2004 05:54 PM

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Hi Ugo, Ithink you are right about the light output and it's impact on the screen.
I'm sure that some of it is down to the colour temperature of the light source. The colder xenon type lamps makes the projected image look "cleaner" to the eyes and therefore gives more impact. That coupled with a screen of high reflectivity would give a nice clean, bright looking image. [Smile]

[Smile]

Mal, the split heat glass on the ST was only really put there I think for still projection. I know a lot of people (me included)who remove the split heat glass on the ST which also alows a little more air flow onto the rear of the gate and a little more light on the screen. Give it a try and see how you get on. Wise on the ditching of the 250W lamp. You get as much light if not slightly more by using the 200 W ESC. EES was made for Super 8 gate and the A1/259 250 W for the 16mm gate. All you do with that lamp is illuminate more round the rear of the gate instead of concentrating the light like the ESC does. Anyway why use the more current consumptive 250W lamp when the proper lamps are now available again from Derann.

Kev.

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GS1200 Xenon with Elmo 1.0...great combo along with a 16-CL Xenon for that super bright white light.

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John Whittle
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posted January 12, 2004 06:34 PM

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Ugo,

The SMPTE standard for projection (theatre and review rooms) is 16 Footlamberts (plus/minus maybe 2). You cannot measure foot lamberts with a light meter because foot lamberts "integrate" the light (that is compute for the shutter with the dark and light alternations) and the meter is held in the light cone, not measured reflected from the screen.

Foot lamberts are very close to foot candles, but Fc do not compensate for the alternations of shutter openings. Remember these are measurements of a light body and not screen brightness which can be greatly affected by gain of the screen and ambiant light (even one of those "exit" signs can through off the image).

A high gain screen tends to have a narrow viewing angle compared to a 1.0 screen which would be a flat matte.

It's not unusual to find theatres that have poor screen illumination. However, remember that the human eye adjusts and if you put up a picture in a TOTALLY dark room, you can get acceptable if not great results.

It would seem based on available equipment, that a 2000 watt xenon is about the largest practical lamp for 16mm and you can work down from there for 8mm and Super 8mm (16mm frame is .380 x .286 inches, 8mm is 1/4 of that and Super 8mm is what about 30% larger than regular 8?).

Probably the biggest factor (and one that would be measured by a proper measurement of lux) is getting all the light focused on the aperture opening. Lux (as I recall) is open gate measurement of light at the gate with the shutter running (thus no effect for projection lens throw or picture size) so figures generally as 30 per cent better for a two blade shutter vs a three blade shutter. There are some other "tricks" that have been tried such as perforating the non prime blade (the prime blade is that one that blocks the light during pull down) which might induce flicker.

Flicker becomes more noticeable with screen size and light scenes. I remember an experiment at an SMPTE meeting in Hollywood several years ago at the Academy of Motion Picture Arts and Science Theatre where one projection (35mm) was run open gate (no film) on a scope screen at 24 fps and then the speed of the projector (nothing else) was increased to 30 fps. The picture, which had slight flicker, evened out and the whole screen was much more even and much brighter. This was part of an arguement to move television production to 30fps in the US, but a very interesting experiment.

Showscan (which uses 70mm at 60 fps) show how "real" film can look with this technique.

John

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Kevin Faulkner
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posted January 13, 2004 05:06 AM

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John, I agree with you about the light being focused on and concentrated on the gate area and this is why I think Elmo also had a lamp manufactured especially for the GS. Lets face it they could have used the std EJL or ELC. I have done many comparisons of lamps in the GS and the ESC once set up correctly wins hands down each time other than going to a xenon lamp. Again I have wondered how other peoples xenon conversions compare to the xenon lamp which Elmo used in their xenon GS as the majority are designed for 16mm. I'm sure Ugo could answer this one as he has made his own converstion to a std GS.
Ugo, how did you choose the lamp you are using? was it just down to availability? Did you manage to focus the light on the gate ok with most of it concentrated on the gate width?

Kev.

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GS1200 Xenon with Elmo 1.0...great combo along with a 16-CL Xenon for that super bright white light.

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Ugo Grassi
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posted January 13, 2004 09:23 AM

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Thank you John for your post.
Kevin, are you talking about the halogen or discharge lamp?
For my halogen GS I use the General Electric EJL (24v/200w). Yes... I know this one is for 16mm but it works very well on the GS. One year ago I found a GE ESC (I think from the last stock; this lamp is no more available from GE catalogue). It's like new (the mirror is clean). We made a test and the EJL worked better than the ESC! About 20 lux more from the EJL. Mistery of the photo optical scienze...
About the discharge, I knew the Osram HTI 250 w32 was made from the super8 under request of Beaulieu factory. But I'm not sure this is not a "super 8 legend". Anyway I had not a big chosen:
an alternative was a lamp of the VIP family, but a technician said me this lamp is for the video projection and his light is poor of red.
The HTI has a good "point of color". This parameter is more precise than the color temperature. The point of color of the HTI seems to be right for the Kodachrome. I prefer - for the Kodachrome - the light from an halogen lamp, but, if I have to use a discharge lamp, the better solution appears to be the HTI.

[ January 13, 2004, 11:06 AM: Message edited by: Ugo Grassi ]

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Ugo

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Kevin Faulkner
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posted January 14, 2004 09:33 AM

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Understood Ugo. I was meaning the HTI lamp. Being a colder colour it helps to make the picture look cleaner. BTW did you know that Derann in the UK now sell the ESC lamp again. It's made by EIKO in Japan who made the original Elmo lamp for them.
All my tests with a Lux meter in the past show the EJL to be lower than the ESC and the ELC the same as the ESC so I was a little surprised at you comments. The EJL & ELC filament is designed to cover a 16mm width gate and the ESC has a more compact filament to cover the width of the smaller super 8 gate so I would expect the ESC to be brighter in the GS? Kev.

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GS1200 Xenon with Elmo 1.0...great combo along with a 16-CL Xenon for that super bright white light.

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Ugo Grassi
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posted January 14, 2004 05:24 PM

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Yes, I understand you are surprise! Me too!
That ESC is GE perfectly working. Do you think is it possible taht one from Eiki is better?
About the ELC I tested one from Osram and I hate like it work. I have the idea the focus of the image is worst with this lamp.
An old technician said to me the dicroic mirror is important for the focus of the image.
Anyway with the ELC I measured less light than the EJL. And you have to considerate I modified the transformer of one of my Elmo to supply at 25v the 200w. lamp. With this work the 24/250 arrives at 24 and something.

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Ugo

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John Whittle
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posted January 14, 2004 09:10 PM

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Ugo,

Since the lamps were designed to cover the 16mm frame (.380 in) have you considered using a condensor to focus the light beam down to the Super 8 frame? In the old days of the big lamps, condensors and reflectors were part of the lamp house and it doesn't seem far fetched to put a condensor in and I'd bet the experiment would pay off. If you use condensor out of an old 8mm or 16mm projector, it'll stand the heat fine. You'll have to experiment to find one that works properly and you have room to install, but if you're losing over half the light, it would make a dramatic difference.

John

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John Clancy
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posted January 15, 2004 02:40 AM

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The ESC lamp differs from the EJL and ELC in being designed for a uniform brightness across the entire Super 8 frame. Do a test using a light meter and you will see it is the same reading until the very edge of the projected frame is reached. This is not the case with the 16mm lamps and the brightness degrades markedly away from centre.

I've just been doing these tests for the next issue of the Derann magazine. The new Eiko lamp stands up very well.

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Kevin Faulkner
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posted January 15, 2004 08:25 AM

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Ugo and John,
The tests I did many years ago along with Philip Jenkins who wrote the reviews for Movie Maker were with the Elmo ESC lamp. I believe these were manufactured by EIKO of Japan the same as the lamps which Derann are selling again so it will be interesting to see what John finds on his tests.
I have today taken delivery of 2 of these new lamps my self and will let you know what I find.
I am in the process of putting a 2 blade shutter in my GS from Argentina so will test the lamp in that once it's up and running again.

Kev.

--------------------
GS1200 Xenon with Elmo 1.0...great combo along with a 16-CL Xenon for that super bright white light.

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Mikael Sundstrom
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posted January 18, 2004 07:12 AM

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The SMPTE standard (16Fl) seems to be a good rule of thumb for projection brightness.

Too bright a lamp to me, would be when the film gets damaged by the heat going thru the gate even at 24 fps!
I wonder if the picture and colors get washed out if the lightsource is to bright ?

Anyway, some day I will know. I have an Osram 400W HTI bulb here. Haven´t got the electronics to control it though, otherwise I would try it in the GS. [Big Grin]

[Big Grin]

[Cool]

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Tony Milman
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posted January 21, 2004 03:54 PM

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Just been reading this heavy duty but fascinating thread.

I think it is only too bright when you find it necessary to wear sun glasses to watch the movie.

Tony [Cool]

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Steve Klare
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posted January 21, 2004 04:26 PM

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I think if your neighbors can see the image right through the wall the lamp is probably too bright!

Trails of smoke coming off the screen might indicate a similar problem.

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All I ask is a wide screen and a projector to light her by...

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