How many lumens do I need?

Originally Posted by jnorth

I think this thread has given the best answer to the how many lumens do I need question and also filling in the blanks on using a light meter. I don't know if I should feel sad or happy for everyone that I was unable to log on sooner to throw an attempt in the answers.

can i complicate it more??

there are so many different types of screens, from opaque, glass beads, grey, white, etc, for different venues

you may be able to save some money by investing into the screen, and dropping your lumen output in your projector

http://www.moesrealm.com/hometheater/screenguide.html
scroll down past the top page ad's

this one has the types of screens and their intended use
http://www.draperinc.com/Screen_Page...efinitions.htm

if your head spins welcome to CMN

[savannahtech]

anything 1000 and up is going to be very bright i still use a 500 lumen projector it is good but not great

[Carl Godsoe]

Originally Posted by savannahtech

anything 1000 and up is going to be very bright i still use a 500 lumen projector it is good but not great

Maybe in a small classroom with no windows.

Originally Posted by Gzsrulz

can i complicate it more??

there are so many different types of screens, from opaque, glass beads, grey, white, etc, for different venues

you may be able to save some money by investing into the screen, and dropping your lumen output in your projector

http://www.moesrealm.com/hometheater/screenguide.html
scroll down past the top page ad's

this one has the types of screens and their intended use
http://www.draperinc.com/Screen_Page...efinitions.htm

if your head spins welcome to CMN

Yes but with the perceived brightness boost there are other factors involved. Some basic factors like life of screen, dirt resistance, or angle of view. The glass beading, I was told be a DaLite rep, can flake off in little bits if not in a good enviroment, some screens have great percieved brightness boosting close to the centre axis but that diminishes as you move off of centre.

If you want to further complicate it how about figuring out what a unit will look like after you have used up a 1/4 - 1/2 of the lamps hours. Is it still bright enough then? Because the lamp diminishes in output over its life, if I found a 2000 lumen projector would just fit the bill I'd probably try and find one with a bit more punch like 24-2500 lumens. That way that movie clip or high detailed image would still have some detail for the last 3/4 of the lamps life.

[bpalermini]

I don't see one issue addressed, although I might have missed it, are you going to use your old projector and screen? If so I would think you would want to match it's appearance. I don't think it would look very good to have one bright screen and one dimmer one.

[Rick]

Originally Posted by rev_65

Nope, and you really can't get there from here...

So if your getting an Exposure Value then you must be taking a reflected light reading?

Can your meter be changed to take an incident light reading? Those are usually measured in foot-candles (LUX in the UK (metric)).

If not then let's work off of an assumption...

Light Value (LV) is equal to EV at ISO 100.
A change in LV of 1.0 = a one stop change in brightness; and a change in EV of 1.0 = a one stop adjustment of the camera. Confirming LV=EV.

From there use the following chart to convert your EV reading to foot-candles. (I'm giving your more numbers than you need, but you'll be able to work out the relationship between values for fractional readings.) Just remember that every +1.0 change in value doubles the number of foot-candles.

__EV_____Foot-Candles

0.00_____0.0097
1.00_____0.0195
2.00_____0.0390
3.00_____0.0781
4.00_____0.156
5.00_____0.312
6.00_____0.625
7.00_____1.25
8.00_____2.5
9.00_____5.0
10.00____10.0

Hope that helps you further.

Help me out, please, with this table. How do I do this with a camera? Point the camera at the screen while set at ISO 100 and f???? and take a reading from the meter and convert using the tables? Is that it? Does f-stop matter on the lens?

[[Admin] danroth]

All anybody needs is 4 Lumens...

and then you make the room REALLY dark.

[kerwin kanago]

Its been a while, so someone correct me if I mess this up...

Zero EV is defined as f/1.0 at one second. For each F-Stop "more closed" than that, you add one. Each shutter speed "faster" (which are nominally 1/2 the time of the previous step) you add one.

So if the camera's light meter says you need F8 at 1/60th at Iso100 that's six stops (1.4,2,2.8,4,5.6, and six speed steps (1/2,1/4,1/8,1/15,1/30,1/60) so EV=12, which, though off the chart would be 40Foot-Candles.

Here's a pretty good discussion of the topic.

[carterson2]

Hi,

I am building a church-quiz projector.

It is to be used on a bare wall with overhead projector at big angle pointing down. Like 45 degrees.

-----ceiling projector pointed down--------
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Any sugestions. All math aside, do I maybe need 2400, or what standard projector model do you think might fit.

The image will probably be 4ft in diameter in a bright well lit hallway.

Q: Any guestimate on lumens and a cheap projector?

(no, I would rather not build a projector if possible).

thanks guys
jim pruett

[[Admin] osborn4]

What size is the screen? And what kind of ambient light is there?

[Brad Weber]

Originally Posted by carterson2

I am building a church-quiz projector.

It is to be used on a bare wall with overhead projector at big angle pointing down. Like 45 degrees.

Originally Posted by carterson2

The image will probably be 4ft in diameter in a bright well lit hallway.

I am a little confused by what a "church-quiz projector" is and that the 4' diameter reference seems to indicate a round image. However, while there are a couple of special short throw projectors that NEC (the 2,000 lumen, 1024x768 WT610E) and Sanyo (the 2,700 lumen, 1024x768 PLC-XL51) offer that might work for such an application, a typical projector is not going to accommodate the short throw or angle to the screen that you noted. You might want to consider using something other than a projector, maybe a large flat panel display.