To determine the correct projector to specify we need to take a look at the purpose of the projected image. Is it for a classroom, home, church or other public venue? Another consideration is what is the intended content to be displayed? Words on a solid background? Video with moving images? Pictures? Spreadsheets?
So what are ANSI lumens, besides being the accepted measurement of the brightness of a projection device? From Wikipedia: “The lumen is the SI derived unit of luminous flux, a measure of total quantity of the visible light emitted by a source.” And more: “ANSI lumens: The light output of projectors (including video projectors) is typically measured in lumens. A standardized procedure for testing projectors has been established by the American National Standards Institute, which involves averaging together several measurements taken at different positions.” So what does that mean in a real world environment?
First let’s look at the intended use. If the image to be displayed is a simple plain background with words in a contrasting color, say black letters on a light blue background, a lower lumens projector may well do the job. The contrast in the image is high and so the eye does not have to decipher small color variances to understand the image. It should be noted that the viewable font size plays a role here as well. A spreadsheet with a lot of numbers and lines will require more light levels and greater contrast from the projection device to be able to present an image so the viewer can clearly determine what the characters are. However, if the intent is a picture or video the light levels must be considerably greater to be able to show the true colors at a real world intensity level. Contrast also plays a significant role in this issue but that discussion is for another time. Suffice it to say that more contrast is better.
Second, what is the venue? If the image is being displayed in a home theater with no ambient light a fairly low ANSI lumen level projector will provide a very acceptable viewer experience but if the venue is a Church with natural light coming from windows or if the service is operated with the house lights turned up, a significantly greater light from the projector will be required.
For the home theater a 2000 ANSI lumens projector with good contrast ratings and high resolution may provide a great viewer experience. However, a 10,000 ANSI lumens device may be required in a Church or other public venue depending on a variety of room related factors. Obviously budget comes into play about now in the discussion and often a compromise has to be reached. To determine where to land on this discussion some time must be devoted to a site investigation with a professional to determine how best to provide a suitable image at a manageable cost. Can the screen be positioned in shadows with little or no light shining directly on the screen location. Can the room lights, or a portion of them, be dimmed or redirected to provide a more viewable atmosphere. These are among the questions an experienced performance room designer can ask and answer.
There is no hard and fast rule regarding ANSI lumens other than it is nearly impossible have too much light while it certainly is possible to have too little light. With the cost of projectors dropping continuously, more brightness can be had for a very reasonable cost. The first projectors we installed in Church venues were 2500 ANSI lumens and cost $10,000.00. Today we are recommending 6500 – 7000 ANSI lumens projectors for most smaller churches at a cost of around $3000.00. It is always best to call a designer and have a professional look at the facility and make suggestions before spending money only to find that the determined solution is unsuitable or even unusable.