CurtPalme.com Home Theater Forum

**Curt Palme**

OK, I've never even seen this question posted before, let alone the answer.

A customer using a CRT for commercial purposes wants to know how large a 9" CRT image can get and still maintain 14fl?

Thanks!

jkruger · Joined: 24 Oct 2007 Posts: 2435 Location: Carlsbad, CA

I guess that depends on how fast you want to cook the tubes?

**Curt Palme** · Posted: Mon Jun 28, 2010 7:02 pm Post subject:

Well, there's gotta be a calculation somewhere if CRTs max out at 1200 lumens though..

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

We need TSE to the rescue!!!

But I think Screen type also matters. High gain screens be higher i assume.

Nashou

virusc · Joined: 11 Apr 2007 Posts: 358 Location: Massachusetts

I can't tell Curt, are you really asking this question or being sarcastic?

widescreen review I believe had a chart just for this with 1,1.1,1.3 gain screens along with DA-LITE and I think Stewart. ANSI for 9" LUG's I believe is around 230(260 if cracked "barco boost"). LCP can be as high as 280 if I remember correctly. Put that in the calculation. If you can't find that the ft/l per square foot at 230ft/l should be easy to calculate.

roland@b4 · Joined: 07 Jul 2009 Posts: 82 Location: Reading UK

I've held onto this for a bit it might be usefull

garyfritz · Joined: 08 Apr 2006 Posts: 12088 Location: Fort Collins, CO

ftL = gain * lumens / area.

But it's a bit more complicated than that. First you have to consider the peak vs. ANSI lumens, as shown in roland's Barco article. Next you have to consider how much of the phosphor you're using. All the projector lumen ratings assume you're using the full 4:3 tube face. If you use less -- e.g. for 16:9 or 2.35:1 screens -- you produce correspondingly less light. And, as jkruger pointed out, getting the full lumen rating might wear the tubes really fast -- I think Sonys are notorious for that.

So let's say your 9" projector is rated 1200 lumens. That's peak. According to the Barco article that would be roughly 165 ANSI lumens. Now let's say the customer wants a 2.35:1 screen. 4:3 = 1.33:1, so you're using 1.33 / 2.35 = 57% of the tube face, so you're only actually going to put out .57*1200 = 684 peak lumens, or .57*165 = 94 ANSI lumens.

So they want 14 ftL. 14 = gain * lumens / area, so area = gain * lumens / 14. Assuming a gain of 1.0, for 684 peak lumens you could have a screen area of 684/14 = 49 sq ft. 49 = x * x*2.35, so x = 4.5; your screen is 4.5' high and 2.35*4.5 = 10.7' wide. Not bad.

But that's peak lumens, remember. If you need ANSI lumens, the screen can only be 94/14 = 6.7 sq ft! 6.7 = x*x*2.35, x = 1.68 -- your screen can only be 3.97 x 1.69 FEET -- basically a 51" diagonal image. You'd probably be better off with a flat-panel.

Pump it up with gain and the screen gets a bit bigger. A gain of 2 means your screen can be sqrt(2) times bigger on each side, e.g. the peak-lumen screen would be sqrt(2)*10.7 x sqrt(2)*4.5 = 15.1 x 6.36 feet.

I wouldn't think CRT would be a great match for most high-light-requirement commercial applications, unless they can live with a small screen.

CZ Eddie · Joined: 23 Mar 2006 Posts: 1601 Location: Austin, TX

There is a huge thread on AVS where everyone was posting what their ft. lamberts were.

Found it:

http://www.avsforum.com/avs-vb/showthread.php?t=862570&highlight=foot

Kiev Savoie · Joined: 25 Oct 2007 Posts: 432

Gary, that was great! I've been pondering what screen size to go with for a scope setup and that fills out the details very nicely. So how many ftL. would you consider adequate for a typical HT setup?
Curt, do you know how big of a screen they are shooting for?

garyfritz · Joined: 08 Apr 2006 Posts: 12088 Location: Fort Collins, CO

I think most typical CRTers (i.e. not stacked G90's, etc) are running in the 10-12 ftL range. I have about 10 on mine and would like more. If you want to have any ambient light in the room, you'll definitely need more and your fade-to-black will suffer.

Kiev Savoie · Joined: 25 Oct 2007 Posts: 432

I plan to watch it mostly at night in cave mode, no lights, hopefully with covered walls. I'm also a stickler for those fade outs, so i guess that means 10 ftL. would be better for me?

**Curt Palme** · Posted: Tue Jun 29, 2010 2:29 pm Post subject:

garyfritz · Joined: 08 Apr 2006 Posts: 12088 Location: Fort Collins, CO

10 ftL would probably do you, Kiev. But it's easy to turn down the contrast if you find it's too bright. It's hard to turn it up if you've already maxed out your setup.

Spanky Ham · Joined: 22 Mar 2006 Posts: 5643 Location: Comedy Central

Kiev,
The recommended level is around 16 ft/lmbs in theaters. I personally like a bright image and would like to be in the 20s. Gain or small image is the only way to do this. One avenue to take would be an UHG torus screen for larger sizes. I forgot how big the screen was, but one 9500 owner got 33 or so ft/lmbs on a Vutec UHG screen. This was measured by Chuchuf. You can sometimes find these screens on ebay for decent prices.

A DIY UHG screen is also an option, but you would be limited by the width of the material. It is simple in concept, but a little harder to implement. Basically, you would spray a translucent coating on some aluminized mylar and attach it to a Torus screen box. Unfortunately, mylar doesn't come any wider than 48". That leaves you with a 105" width scope screen.

garyfritz · Joined: 08 Apr 2006 Posts: 12088 Location: Fort Collins, CO

Yeah, I'd say 10 ftL is a bare minimum. Like I said, I wish I had more. I know some people run lower than that but I wouldn't. 14 would be good, 16 would be better, but I doubt many CRT owners are getting 16 or more without stacking, blending, or high-gain screens. Unless they have a really small screen.

donaldk · Joined: 17 Jun 2008 Posts: 308

A fellow forum member has been playing around with his 8"-er:

http://www.htforum.nl/yabbse/index.php?topic=93867.msg1569085#msg1569085

donaldk · Joined: 17 Jun 2008 Posts: 308

Spanky needs to go find an old Vutec 120". Gain is only 13 at dead center.

Kiev Savoie · Joined: 25 Oct 2007 Posts: 432

14 ftL. sounds reasonable. I'm drawing up something right now so we'll see what can be done.

Kiev Savoie · Joined: 25 Oct 2007 Posts: 432

I'm terrible at math but here is what i have so far:
gain = 3.5
ansi lumens (G70)= 240
screen area (65.25"*36.7")= 16.6296 sq/ft
1.33/1.78= 74.7%
.747*240=179.3258
ftl.=gain*lumens/area
3.5*179.3258/16.6296=
37.7438???
This can't be right. where did I go wrong?

ecrabb · Posted: Wed Jun 30, 2010 6:29 am Post subject:

Actually, that's probably not far off. It's the gain and the small screen that are both jacking your fL figure way up.

I'm running my G70 on a 96x54 DW... About 1.3 gain, IIRC. First, 96x54 is almost exactly half the area of your 65x36... But, your 3.5 gain is also nearly triple.... So, that's 6 times the reflected light from gain and area... Which jibes with my calculated number of about 6fL.

I can tell you that in practice it isn't nearly as bad as it sounds. I can get right at 12fL on the 100 IRE window, but obviously, that figure drops precipitously on high-APL scenes.

But, my room is tight with wide viewing angles. I couldn't have done high-gain even if I'd wanted to... And I didn't want to.

With your intended screen size, you don't need to go high-gain. At 65x36 on WilsonArt, you can easily get 24fL on low-APL scenes, and probably half that even on higher-APL scenes. If you want to go high-gain, you can go bigger, or if you want to stay smaller, you don't need high-gain.

SC