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Buying Guide for Business Projectors

Projector Brightness

The amount of light a projector can put out is measured in ANSI lumens or just "lumens" for short. The brighter the projector, the higher the ANSI lumen rating, and (all else being equal) the more it costs. (By the way, some manufacturers are now quoting "Center Lumens" instead of ANSI lumens because the number is larger--measuring just the brightness at the center of the screen rather than the average brightness overall, as the ANSI method does. Don't compare one vendor's ANSI rating to another's Center rating as they are apples and oranges.)

Screen Gain

Two things determine the brightness of the picture on the screen. One is the amount of light coming from the projector. The other is the reflectivity of the screen, which is typically quantified in "gain." A screen with a gain of 1.0 will reflect back to the center viewing position the same amount of light that strikes it. A screen with gain greater than 1.0 will focus more of the light energy back toward the center viewing position and less toward the sides, making the picture look brighter when viewed from the center position. If a screen has a gain of 1.3, it will looks 30% brighter at the center viewing position than it would with a 1.0 gain screen. If the screen has a gain of 2.0, it is twice as bright, etc.

The big downside to high gain screens is that, since they focus more of the light energy back toward the center viewing position they reflect less light toward the sides. That means the picture gets dim in a hurry when you move toward the side and off the center viewing axis. So if you have people seated at various angles to the screen it is best to have a low gain screen so that everyone can see a reasonably bright image. On the other hand, if your seats are all very close to the center viewing axis, a high gain screen can give your viewers a brighter image without you having to buy a brighter projector.

Picture Brightness

The projector's light output and the screen's gain together determine how bright the overall picture looks. This is ultimately the important thing, and it is typically measured in foot-Lamberts, or simply fL. So as the ANSI lumen measurement tells you how much projector light energy is hitting the screen, the fL measurement tells you how much light is being reflected back.

How many foot-Lamberts do you need?

The ideal brightness of your picture depends on the application and how much ambient light there is in the room. In a classic dark home theater, the official SMPTE recommendations are for 16 fL. However, most people actually prefer a picture that is a bit brighter than that, so we would typically recommend spec'ing it in at 20 fL. Keep in mind that all video display systems (projectors as well as flat panels) will lose brightness as their light sources age. If a projector has a high pressure lamp you can periodically install a fresh lamp and bring the unit back to full power. With laser or LED systems, the degradation is slower but permanent. Either way it makes sense to factor this into your overall brightness solution.

In modest to moderate ambient light, you need a much brighter image to produce sufficient contrast. A rule of thumb would be 40 fL, but it depends on the amount of ambient light and the reflectivity of the room itself. In a conference room with normal lighting, 60 fL would be the ideal target.

Calculating Foot-Lamberts

In order to determine how many foot-Lamberts a given projector and screen combination will create, you can use ProjectorCentral's Projection Calculator. The variables you can adjust are these:

  • Screen size: For any given projector, the smaller the screen size the greater the fL, since you are concentrating all of the projector's light energy into a smaller space. As you enlarge the screen, the fL number drops.

  • Screen gain: As you will see, once you load any projector into the Calculator, it defaults to an assumed Screen Gain of 1.0. If you need more foot-Lamberts and have not yet purchased a screen you can adjust the screen gain rating to indicate what effect it will have on total image brightness.

  • Zoom lens position: In general the wide angle end of a zoom lens will allow the projector to maximize its lumen output. As you move the projector back from the screen and use the zoom lens to throw a narrower cone of light, the light is curtailed. The Calculator makes some adjustments to anticipated fL to account for this effect.

  • Application use: Commercial projectors have ANSI lumen ratings based on maximum light output. When the light source is driven to maximum it usually results in a picture that has a green tint or bias. This may or may not be objectionable for data presentations, but it is usually problematic for video. Once a projector is color calibrated for best video its lumen rating drops significantly. So you can select which application uses you are concerned with and in most cases the Calculator will factor the fL number down if you select Video, to account for reduced lumen output after color calibration.
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Comments (6) Post a Comment
Ed Dusang Posted Mar 14, 2019 10:07 AM PST
I have two long throw Infocus projectors with a long through lenses. our screens are 110" and 53' ft distance in our church. We need to replace them with either new or used in our budget.Help
Rob Sabin, Editor Posted Mar 16, 2019 9:43 AM PST
Ed, there's a lot more that goes into this decision than knowing screen size and throw distance. I suggest you get in touch with local integrator or contact one of our authorized resellers to talk you through it.
Tony Chalinor Posted May 24, 2019 11:27 PM PST
our community theatre has currently an IN 42 In-focus large venue projector, it is limited to 1080i fed by component. Would like an idea of a current projector with HDMI input and other modern input features. The projector struggles to provide sufficient light output for current use.It is throwing the picture about 20 metres and screen size is approximately 6.5 x 3.5 metres high. Do not know what the roll down screen ratio is. Has a relatively new light source in it. regards A.J.Chalinor
Rob Sabin, Editor Posted May 25, 2019 8:47 AM PST
Tony,your IN42 is rated for 3,500 lumens brightness with a new lamp, and according to our projection throw calculator it's not really even capable of an image of that size from that distance (about 65 feet?. So even if you're mistaken about the precise detail here it's obvious that the projector is woefully inadequate to the task...and that's without even knowing if you are using it with modest ambient light.

If you've shared truly accurate information about image size (rather than overall screen size) you would need a really large and bright (and expensive) projector to pull it off. I'm guessing though, that if you've been making due with your IN42 it's a much less demanding setup in reality and a step up projector in the 5,000-6000 lumen range will probably work for you. You really should bring in an A/V pro to assess it though to be sure.

I don't know what your budget is, but I would look through the scroll of the projector Road Tests that you'll find on our homepage and look for something rated for 5,000 lumens or higher range. You probably want at least WUXGA resolution at this point, which is basically 1080p. If you opt for spending on one of the less pricey laser projectors that have come out recently, you'll be able to justify the higher up front cost by avoiding the purchase of new lamps later -- you never have to replace the bulb in these units, which is usually several hundred dollars per replacement. Also, if the 5,000-6,000 lumens is adequate to the task and gives you some real punch, and you get at least WUXGA resolution, you may expand your possibilities of renting your space for entertainment or business presentations/events to help recoup costs. You've had a 3LCD projector all this time and I'd recommend you stick with that for a couple of technical reasons given your setup. The Epson 610U($3,500 street price) would probably work well if you could swing that. But there are others out there in this brightness/resolution category that use lamps if you're looking to save money up front, as well as projectors offering resolution similar to your IN42 (WXGA by today's widescreen standards, 1200 x 800 pixels) that would cost less. The main thing here is lumen output mated with a projector that can give you the image size you want from your established throw distance. Measure those things out carefully, select a couple of projectors to look at, then find them in our Throw Calculator to see if you can get the image you need at distance.
AR1964 Posted Nov 1, 2019 3:31 AM PST
Very clear and concise article, thank you. Our projector will be wuxga 9900 ansi lumen, but the screen ratio (an outdoor building) is closer to 3x4 (portrait). Documentation states it is possible to use the projector on its side to get a vertical image. The conetent (video, images, graphics) has been created to fit the building (mapping) in files matching 1920x1200. There is alot of black space either side. This means a lot of the projected image will be effectively not used (the part falling off the building). This works on site but I was considering using the same projector but in a resolution that matches 4:3 such as xga, so that more of the pixel area of the chips are used. Will this effect quality of image and will it increase brightness as more of the projected light will fall on the building?

To clarify: Using a WUXGA projector in portrait, changing the ratio from 16:10 to 4:3 to project content which is 4:3

Or am I barking up the wrong tree?

Thanks AR
Rob Sabin, Editor Posted Nov 1, 2019 7:49 AM PST
AR, I'm afraid I don't know the answer to this, other than to suggest that if you give the projector an XGA res image the detail will be considerably hurt and the likelihood is that the projector will simply mask or turn off the unused pixels on the chip rather than scaling up to use them. Perhaps you should try some experiments to see how the projector behaves.

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