Five Factors Affecting the Brightness of Projected Images

This may seem like a very specialized topic for a meeting planner but it is actually something that all meeting planners need to learn at least a few basics about. As mentioned in previous posts, I will often defer to the expert audio-visual (AV) techs when I need specialized knowledge about AV for my meetings. However, I also make sure that I understand enough to be able to keep up with what they are doing. Learning these five factors has been a big help to me in doing just that when it comes to projectors – especially those LCDs that every presenter seems to want these days…

So what are the top five factors that determine how bright or powerful the projector needs to be? Well, I’ve listed them here in order of importance – from most to least – as I see them.

Ambient Light: Essentially, this is “how much light is there in the room?” The more light there is, the more light (brightness) you will need the projector to put out in order to get a clear image projected on the screen that everyone can easily see.

Size of Projected Image: Effective brightness drops as the image size increases. This is due to the fact that the projector’s light output does not change while the surface area goes up, which means less light per square foot on the screen. A more powerful projector can overcome this. It is worth noting that the light levels can drop precipitously as the image size increases. According to some estimates I’ve seen, doubling the image size can result in as much as a 75% reduction in image brightness!

Aspect Ratio: The standard aspect ratios that people are used to seeing are 4x3 (TV) and 16x9 (widescreen) but there are many more out there... In essence, though, the higher the aspect ratio, the more light the projector needs to produce to maintain image brightness due to the increased area that needs to be illuminated.

Projection Surface: Different surfaces have different refraction rates; that is, light “bounces” off of them differently. Some surfaces reflect more light while others reflect less. This can affect how the eye sees images that are projected – not just the colors of images, but also the clarity and brightness. If you are using a standard screen, you don’t really need to worry about this factor.

Projector Calibration: I’ve listed this one last because it the one factor that I have rarely, if ever, actually seen have an effect on the projected image. It is possible, but very rare. Typically, the other factors make such a difference that this one is accommodated without the audience even being aware it exists. Every projector is calibrated slightly differently. They may be near to identical when they leave the factory but, through use and “wear and tear”, they can become slightly “off” from others of the same make and model. A replacement bulb might also be an issue, changing how the final image looks onscreen – even when all other factors have been accounted for.

When setting up a projector and screen for a presenter, I always try to take these factors into account. I am not always able to minimize the effects of each factor but I can usually adjust for that by selecting a more powerful projector – one that puts out more light. Testing during setup is very important as well, so you can make sure that you have done everything you can to make the presenter look good. If they remember the presenter – and not how the AV looked – then you have done your job…

~ Karl Baur, CMP • Project Director, RDL enterprises