[Harpmaker]

Can't you use your spot meter to find how many lumens your PJ is really shooting? Just shoot a 100% white field and take a reading.

I don't think I've ever seen a definition of what makes a "light cannon" or a "low lumen" PJ.:scratchhead:

I know in testing I had a very watchable image with my BW screens at a measured 12 foot lamberts brightness. I don't think most would call that screen as being hit by a "light cannon".

 

[Harpmaker]

And lumens would be equal to foot candle times square feet, right?

If that's correct I'm currently at 136 lumens...

That seems awfully low!

100% white field measured 4.6 foot candles. I measured as low as 3.9 and as high as 5.0. I took the average as that was the measurement at the center of the rectangle.

100" screen = 29.6 square feet

Someone tell me I'm measuring/converting this wrong!

mech

4.6 fL. is a very dim screen!

Was this a reflective measurement of the screen or a incident measurement of the PJ beam with the meter at the screen (I know your meter can do both)?

Lumen/sq ft, foot candle and foot lambert are all the same. Lux multiplied by 0.0929 = foot candles. Conversely, foot candles multiplied by 10.7643 = Lux. Lux = lumen/square meter.

 

[Harpmaker]

Would this help? I found this converter from foot-candles-to-lumens.

Thanks for that Tony! :T That particular converter isn't of much use since the two measurements are the same. , but that site has a really nifty luminance converter that works great!

http://www.unitconversion.org/unit_converter/illumination-ex.html

 

[Harpmaker]

That would be a dim bulb I guess! No reflective measurement, just an incident reading. I didn't have a ton of time before I left for work so I'm not 100% sure if I had the meter setup correctly. I'm going to double check it tonight. It can take incident readings a number of different ways and I was in a hurry.

Then again, my bulb does have 2000 hours on it. :dontknow:

Yeah, it would be a good idea to take another reading making sure your meter is set up correctly (you almost have to take a course to learn how to use that thing! :laugh. I'm not making fun of mech or his light meter; that thing is a seriously wicked meter!

So my calculation was correct in 4.6 X 29.6 = 136 lumens?

That's what I get assuming a 100" diagonal 16:9 screen. You are having 4.6 fL. of light hitting a square foot of screen, multiplying your screen footage by 4.6 gives you 136 total lumen/sq ft for the screen.

I played around with the Pro Calculator at PJ Central and your PJ in video mode is showing 14-16 fL for that screen size, depending on the PJ's zoom setting. I have found that my PJ actually shoots out about half of the fL. this calculator shows, I assume it's because I'm using Econo mode. If you are using Econo mode too that could well cut your true fL. figure down to 7-8 fL. with a new bulb! This is all supposition of course.

Take your time and get an accurate PJ output measurement and then change the bulb and take another; this will tell you what is REALLY happening with your PJ. :T

You all are probably getting tired of hearing me say this, but I wish people would spend the extra money (less than $50 to your door) to get a simple light meter so they can know what their PJ's are really shooting instead of just guessing or going by a calculator that may or may not be right.

 

[Harpmaker]

Thanks Don! I'll putz with the meter some more tonight before bed time and report back tomorrow.

What's really intriguing to me is that if those numbers were true, everything said elsewhere in the past (and more than likely currently as well) is wrong.

mech

I agree, but rather than say "is wrong", I would use "could be wrong". :bigsmile:

Just as no two cars get the same exact mileage, even if they are the same make and model, no two PJ's are going to have the same light output. Take individual differences between PJ's and add in the unknown of whether the manufacturer used video or business illumination figures, and you get one big mess. Throw in PJ setting changes due to screen calibration and... :dontknow:

If someone could actually measure the output of projectors at various settings (business and video modes, normal and econo lamp settings) and make a table, it could be of real use to determining what PJ to use with our screen. The closest this comes to being a reality is various reviews in magazines and on the web, but even they don't take the time for as in-depth testing as I would like to see.

 

[Harpmaker]

Ok I quickly redid it using the projectors white test pattern. 11 foot candles.

11 X 29.6 = 325.6 lumens

That's a bit more realistic. So.... am I a 'lower lumen' pj guy?

mech

Ahhh, there's that 'quickly' again. :nono: Haste makes waste, I keep proving this over and over again myself. :laugh:

Did you redo the test with both a 100% white field image and the PJ's test pattern, or just the PJ pattern alone? I would be very interested to know if they differ.

The advantage of using a 100% white field image from a known source, such as the 'Digital Video Essentials' DVD, is that it is an industry standard; I'm not sure the patterns built into PJ's are.

At 325 lumens I would say that is fairly 'low lumen'. This of course, is with a bulb that has almost reached end-of-life. I would suspect you will easily double that figure with the new bulb (or I guess I should say 'lamp'), and perhaps get even more brightness.

Now the big question: does your screen image look dim?

 

[Harpmaker]

Glad to hear the 100 IRE image and the PJ's built-in white image seem to be the same; that speaks well of Mitsubishi in my book.

You are also verifying my opinion that 12 fL. is plenty of light for a BW screen. :T