Digital Projection's Screen Brightness Calculator:
A Useful Tool for Designing High-Impact Projection for Any Venue

The answers to the questions of how bright a projector needs to be, or how big a screen can be employed on a job, depend on viewing distance, ambient light level, content to be displayed and desired image brightness. DPI created the Screen Brightness Calculator to assist in defining the optimum mix of screen size, screen gain, projector lumens and contrast, for any venue.

To use DPI's Screen Brightness Calculator, the only factors you need to know in advance are the ambient light level that will be falling on the screen and the display objectives for the venue. Armed with this information, the calculator can guide you in selecting the perfect combination of projector lumens and screen size and type, to create optimum imagery in your applications.

The Screen Brightness Calculator can also assist you in determining screen dimensions (height, width and diagonal) for any aspect ratio screen. Simply select the required screen aspect ratio and define any one of the three screen dimensions, and the remaining two dimensions will calculate automatically.

To put the Screen Brightness Calculator to work, select your projector resolution and the required screen aspect ratio, then simply type the relevant numbers into the yellow boxes. Your goal is to match screen dimensions, screen gain and projector lumens, such that the system delivers enough Ft. Lamberts to overcome the venue ambient light level and produce suitable environmental contrast ratios. Target Ft. Lamberts for different types of venues are provided as examples within the Screen Brightness Calculator.

Experiment with the Calculator by trying different screen gains, screen sizes, aspect ratios, projector lumens and venue ambient light (falling on the screen). Notice the impact these factors have on image performance.

When using the calculator, be aware that projector brightness in lumens and the projector's contrast ratio must be as accurate as possible. Some manufacturers exaggerate these values in their specifications. Don't use "spec" data if it is suspect, use real data. Additionally, projectors that use Metal Halide lamps produce much less light when calibrated to D6500. Finally, all projection lamps lose light output as they are run through their useful life. Thus, the actual values you create using the Screen Brightness Calculator should be 25-to-50% higher than the target values referenced in the Calculator. This will help assure the projected imagery remains high impact through the entire life of each lamp.

CLICK HERE to start using the Screen Brightness Calculator.

IMPORTANT: The Caculator is a Microsoft Excel file and uses "macro" functions. In order for it to work properly, the Excel program on your computer must be set-up properly. This is done by setting Excel's Security settings.

If you don't know how to do this, follow these simple instructions (BEFORE opening the Calculator):

If you have any further problems, please contact your IT Manager or your DP Regional Market Development Manager.

A key factor to consider when selecting a projection display is understanding the minimum Total Environmental Dynamic Range required to achieve killer imagery in the target venue.

The term Total Environmental Dynamic Range (TEDR) describes the actual contrast ratio achieved in a venue, including the impact of ambient light. Thus, the TEDR value defines the dynamic range, or contrast, the viewers actually perceive. You will see, even in venues with a minimal amount of ambient light, the TEDR value will be much lower than the contrast ratio defined in projector specification sheets.

The method of calculating TEDR is relatively simple:

TEDR = Projector Screen Brightness / (Projector Screen Black Level + Ambient Light reflected by the Screen)

The most complicated part of the process is converting the three values in the formula to one standard of measurement. For purposes of this article, we will use Foot Lamberts (FtL). FtL is a measurement that defines the light being reflected by the screen.

Step 1: Projector Screen Brightness

Convert the lumens produced by the projector to Projector Screen Foot Lamberts (PFL) using the following formula:

PFL = (Projector Lumens / Screen Area in Sq.Ft.) X Screen Gain

Step 2: Projector Black Level

Projector Black Level (PBL) must also be defined in terms of Foot Lamberts. The approximate PBL value can be calculated in terms of lumens, by simply dividing the projector lumen spec by the projector's specified contrast ratio. As an example, a 1,000 lumen projector with a 1000:1 contrast ratio, in theory, should produce a PBL of 1 lumen. We then use the same formula we used in step one to convert the lumen-based PBL to a FtL based value (PBFL).

PBFL = (PBL in Lumens / Screen Area in Sq. Ft.) X Screen Gain

Step 3: Ambient Light

For new construction, defining the ambient light that will fall on the screen is best done with the help of the lighting designer. For existing installations, we recommend taking a real-world measurement using an accurate incident light meter positioned where the screen will exist. Hold the meter parallel to the screen surface aimed toward viewers' position. Many luminance meters measure incident light in terms of Lux. If this is the case with your meter, the Lux value will need to be converted to Foot Lamberts.

To convert Lux to Foot lamberts, use the following two formulas:

1. Convert ambient incident Lux to Lumens:

Ambient Incident Lumens = Ambient Incident Lux X Screen Area in Sq. Meters

or

Ambient Incident Lumens = Ambient Incident Lux X (Screen Area in Sq Ft / 10.56)

2. Convert Ambient Incident Lumens to Ambient Incident FtL (AIFL)

AIFL = (Ambient Incident Lumens / Screen Area in Sq.Ft.) X Screen Gain

Step 4: Bringing it All Together

Now that all of our variables are expressed in terms of FtL, we can use the formula to calculate the TEDR that will be achieved:

Total Environmental Dynamic Range = Projector Foot Lamberts / (Projector Black Level in FtL + Ambient Incident Light in FtL)

Or, stated in short form, using our acronyms:

TEDR = PFL/(PBFL + AIFL)

Putting Total Environmental Dynamic Range to Work for Your Customers

As an approximate guide, DP recommends Total Environmental Dynamic Range targets for the application categories listed below:

- Conference Room (PowerPoint, Spreadsheets, some Video or HD): 10-20:1 rear or front-screen
- Home Media and Entertainment (Video, HD, Videogames, Web): at least 15-30:1 rear-screen, 30-50:1 front-screen
- Worship (Hymn Text, IMAG, some Video): 10-20:1 rear-screen, 20-40:1 front-screen
- Staged events and broadcast applications (CG content, Video and HD): 30-50:1
- Theater or screening room (Video, HD, CG content): at least 500-1000:1

Of course, customer preferences and content present additional variables, meaning no simple set of rules will work for every application. However, as you start to consider TEDR in the systems you design, you will define the TEDR values that work for your customers as well as the projector, screen and lighting configurations that deliver those TEDR values.

It is all about dynamic imagery. The final simple rule: Reduce ambient light as much as possible. If TEDR values are still too low, bring more lumens to the task and consider the use of high gain and/or rear projection screens.

Using classic HIGHlite lenses on the new Highlite Professional series

Many of our customers already own optics for our classic HIGHlite projectors (4100gv, 5100gv, 4000Dsx and 6000Dsx). The classic HIGHlite lenses were designed to be used with projection systems based on F3.0 optics. The new HIGHlite Professional series lenses have been designed
to work with projection systems that employ F2.4 optics. Thus, the classic HIGHlite lenses are
not optimized for the optical system employed in the new HIGHlite 'Pro' series, which is based
on F2.4 optics.

When a classic HIGHlite lens is used on a new HIGHlite 12000Dsx+, approximately 20-25% of
the projector brightness is lost, due to the mismatch in the F-rating of the optics. However, a positive effect is a 20% improvement in the projector's contrast ratio. DP has actually measured contrast in excess of 2500:1 when we have evaluated HIGHlite 12000Dsx+ projectors using
classic HIGHlite lenses.

It is also important to note, the throw ratios on the classic HIGHlite lenses were based on the projectors' .9 inch, 1280 pixel-wide SXGA DMD's. If a classic lens is used on a new HIGHlite 12000Dsx+, the throw ratio has to be re-calculated to account for the fact that the 12000Dsx+
uses .95 inch, 1400 pixel-wide SXGA+ DMD's.

In essence , the bigger DMD means a bigger light patch exiting the lens, so the classic lens
gets shorter when used on the 12000Dsx+ platform. Recalculation of the lens throw ratio is
pretty straightforward:

• Multiply the original throw ratio of the classic HIGHlite lens by this factor (.914)

The result is the throw ratio the classic HIGHlite lens will provide on the new HIGHlite
12000Dsx+. As an example, a classic HIGHlite 2.5 - 4:1 lens will actually be 2.285 - 3.65:1
when used on a HIGHlite 12000Dsx+ projector.

There are a couple of important things to remember. First, classic HIGHlite 1.5-2.5:1 lenses need
to be specifically denoted as "High-Brightness" to be used on a HIGHlite ProSeries projector. Specifically, the DPI part number LA00263 (the lens may be marked TL-1ZH), confirms the High- Brightness version of the lens. Use of the standard brightness 1.5 - 2.5:1 classic HIGHlite lens on
a HIGHlite Pro series projector will cause the lens to eventually discolor and fail.

Additionally, an adapter ring is required to enable compatibility between the classic HIGHlite lens and the new lens mount used on the HIGHlite Pro series projectors. The "Classic HL Lens
Adapter" is listed under "Options" on the HIGHlite Pro series page in our Commercial AV and
Home Cinema Dealer pricing. It carries a list price of $495, and provides a very efficient path to repurposing classic HIGHlite lenses for use on the new HIGHlite Pro series.

Perforated Screen Tips

In many home entertainment applications, a perforated screen is often utilized. As in commercial cinemas, this allows transparent sound to radiate from the center channel behind the screen.

Although rare, when using any fixed resolution projection device, including DLP™ technology on a perforated screen, a moiré pattern may sometimes be a visible artifact. The moiré is caused by the interaction of the DLP™ mirror array, or the source frequency, with the screen perforation pattern.

If you experience this phenomenon, you can minimize moiré by applying some or all of the
following steps:

• Slightly increase the size of the projected image. Use projector blanking to mask the overshoot of the image.
  
• Adjust the projector pixel clock for the source.
  
• If the above options do not work, slightly defocus the image.
  
• If all else fails, consider utilizing a perforated screen with a different perforation pitch.
  

Aspect Ratios and Screen Dimensions

Some of the most common questions we receive on our applications support line have to do with calculating screen dimensions as they pertain to various aspect ratio's.

With this handy table of formulas, you will be able to ascertain the screen size, starting with only one dimension and the aspect ratio required for the application.

720p or 1080i?

For the best image possible on DPI's precision displays that employ 1280 x 720 resolution DMD's (iVision HD-7, dVision HD, Mercury HD, Mercury 5000HD), set the output of your DVD player or Satellite receiver to 720p. By doing so, you match the pixel output of the player or Satellite receiver to the native resolution of the projector.

720p signals benefit from progressive scan, meaning each frame is displayed in its entirety before moving on to the next. By matching 720p signals to native 720p projectors, you minimize scaling artifacts as the image does not have to be "de-interlaced" and the resolution of the source does not have to be "scaled" to match the native resolution of the projector.

You can apply this rule of thumb to all fixed matrix displays. Whenever possible, match the source resolution to the native resolution of the projector, monitor or flat screen. The benefit is amazing and crystal clear.