Today's compact yet powerful front streaming videos projectors will leave you with a too bright an image to watch! This being especially so if you intend to watch a projected image in a darkened room ? which after all, is virtually all typically the case with a home theater setup.
Defining ?Screen Gain?
Before proceeding with our discussion, it's vital that 1 has a full understanding of what the term ?screen gain? is all about.
It might sound strange that we talk about ?gain? when in reality a projector screen is nothing even more than a passive device. Yet there exists - it's all a question of how the screen surface distributes the reflected light.
Screen gain is a measurement of the reflectivity of the screen surface. It measures the ability of the screen to direct incident light back to the audience.
The gain number represents the ratio between incident light and reflected light. A flat matte white surface has a gain of about one. A gray screen has a gain less than one and so, it attenuates incident light. Reflective screen surfaces have gains greater than 1; these projection screens direct even more incident light back to the audience.
Gain is always measured in front and perpendicular to the screen at the point of maximum brightness; this represents peak screen gain and happens at the 0 viewing angle perpendicular to the screen surface.
For a screen with gain greater than 1, the gain drops as 1 moves to the side and see the screen at an angle to the perpendicular drawn from the center of the screen. The angle at which screen gain falls to half the peak is known as ?half gain viewing angle?. A host viewing the screen from this angle will see the image half as bright as the individual seated at the center. The even more 1 moves further away from the center, the dimmer the projected image will be.
The higher the peak screen gain, the narrower the supported viewing angle. This is the cost 1 has to pay for a higher screen gain - the higher projector screen gain at the center is in fact achieved by directing even more light towards the center viewing positions rather than letting for a uniform reflected light on top a wider angle of review.
Projected Image Brightness:
Matching the projection screen gain with the ambient light and the streaming video projector output is essential if you happen to want to make sure that you will end higher with a correct level of projected image brightness.
This is an very vital issue. Don't forget that a basic requirement for a neat movie experience is a comfortable environment. This means that the time 1 spends watching a movie should be as comfortable as possible. Exposure to a bright projected image is pinching on the eyes - even when this is for just a couple minutes, least imagine when watching a two-hour movie.
A Tricky Matching Process!
Ambient Light Conditions, Image Brightness & Screen Gain
A projected image is at its best when viewed in sum darkness - this helps take away any visual distractions - rendering it simpler for the viewer to get deeper immersed into the movie action.
In the home, achieving a totally darkened room is almost impossible except in the case of the dedicated home theater setup. The amount of ambient light present has an impact on the resultant projected image contrast. This calls for the require to increase the image brightness to maintain the correct level of image contrast.
The tricky issue is to arrive at the correct level of image brightness for a pre-set level of ambient light. This in watch that projected image brightness is a function not only of the projector output, however as well of the screen gain, and image size.
The explanation that follows should help you get a better understanding of the relationship that survives between these 3 inter-related parameters.
Display Brightness and Screen Gain
The brightness output level of your projector is a measure of the projector output power in terms of light intensity. Please keep in mind however that the resultant projected image brightness is a different issue. Image brightness falls in proportion to the area of the projected image size - the bigger the projected image is, the dimmer it will look for a fixed level of projector brightness.
The projected image brightness - even more specifically the Luminance level for a projected image, is a measure of the light reflected from the projector screen area. It's measured in foot-Lamberts, and is defined as:
ANSI-lumens of your projector divided per square footage of Screen.
(Note that 1 foot-Lambert is equal to one ANSI lumen per square foot.)
To arrive at the actual level of light reflected from the screen surface, the above result must be multiplied per projector screen gain.
A useful reference just here is what has been defined as 'sufficient brightness' per Society of Motion Pictures and Television Engineers, also known as SMPTE.
In standard 196M, the SMPTE determined sufficient brightness for showing motion pictures in a darkened room employing a unity gain matte white projector screen, as twelve - twenty-two foot-Lamberts. In practice, the luminance target level is set to about sixteen foot-Lamberts, while the average bright scene brightness level in a movie theater is generally sixty percent to seventy-five percent of this target value.
Display brightness is in itself an completely subjective term; what?south even more, it's all relative to the amount of ambient light falling on the screen surface.
The following rules of thumb would surely come to assistance in this respect:
- The contrast ratio between the projected image and the ambient light level falling on the screen should be at least 5:1. This is necessary for the eye to perceive a real impression of brightness. If this contrast ratio isn't achieved, the projected image will not be considered of adequate brightness level.
- When viewing takes place under normal ambient light conditions, the luminance level should be close to fifty foot-Lamberts. This level of luminance is created from the fact that SMPTE indicated a target level of image brightness for a CRT TV as fifty foot-Lamberts, this in see that a TV is commonly viewed under normal ambient light. 1 might argue that TV is a entirely different technology ? this is true, however this target level for image brightness or even luminance, however holds fantastic for virtually all circumstances.
How does all this translate in practical terms?
If 1 is viewing an image in usual extremely low ambient light conditions (say less than two foot-candles - the same as around twenty-two Lux), then the minimum expected light level ?illuminating? the screen surface should be around ten foot-candles to achieve sufficient image contrast.
For a matte white projector screen surface with a screen gain of 1, this translates to a minimum of ten foot-Lamberts in terms of light ?reflected? from the screen for image brightness. This is close to the SMPTE usual requirement for average luminance when viewing pictures in a darkened room.
Similarly, if viewing were to take place under normal ambient light room conditions (typically ten foot-candles or even 110 Lux), applying our 1st rule of thumb to achieve the mandatory contrast level would consequence in a luminance level of fifty foot-Lamberts (approx. 540 Lux) for the equivalent matte white projector screen surface. This is also in line with the target luminance level detailed in rule two for viewing under normal ambient light conditions.
- Note:
- Light illuminating a surface is measured in lux (Lx = lumens/m2), or even foot-candles.
- Light reflected from an area (luminance) is measured in candelas/m2 (cd/m2) or even foot-lamberts (fL).
Currently, let?south think about as an pattern what will occur with different projector screen gains for say a given 1000 ANSI-Lumens projector and a 100" diagonal screen size.
Projector Screen Gain one one.five two Image Luminance in foot-Lamberts thirty forty five sixty
It's clear that our 1000 ANSI-Lumens projector would make a too bright an image when the latter is viewed in a darkened room, even when applying a standard matte white projector screen with unity gain. Similarly, apply of this projector in conjunction with a projector screen surface having a gain of two could result in a too bright an image even when viewing takes place under normal ambient light conditions.
Andrew Ghigo ? A Telecoms/Electronics engineer by profession, with specialization in digital switching and telecoms fraud management systems.
Editor and publisher of http://www.practical-home-theater-guide.com - a site dedicated to all home theater enthusiasts with the scope of serving as a comprehensive home theater guide to home theater systems, product reviews and home theater design.
This article is an excerpt from a series of guides appearing under the home theater screens part of the site.
Article source: http://www.topiccenter.com/Computers-and-Technology/