AV Unit

Which projector? Does brightness matter?

I often get asked by customers ‘which projector should they hire?’. Its understandable, after all there is quite a range to pick from and if you don’t use them every day or you’re not familiar with the terminology it can be a bit confusing.

First, let’s be clear, we are talking here about projectors for common everyday use. The sort of thing you might use for a presentation, meeting, conference etc. If you are talking about big screen images, super wide screen, edge blending, projection mapping, cinema or other specialist applications then there are far more things to consider. We want to keep this simple and answer the most common questions. So let’s press on….

Put simply, brightness is one of the key features that you need to consider. Picking the right model is important to get something that will do the job for you but also has a considerable affect on the cost of hiring or buying it. After all you don’t want to go to the trouble of projecting an image and find that it’s all washed out and you can’t read the text or see the picture.

Projector brightness is usually quoted as a number and expressed in Lumens. Most often it is stated as ANSI lumens. ANSI (American National Standards Institute) is a standard way of measuring the brightness by taking several measurements at points on the screen and calculating an average value. Basically, the higher the number the brighter the projector will be, but watch out as some cheeky manufactures are starting to quote brightness as ‘centre lumens’ to make it sound brighter.

Another thing to think about when comparing brightness between projectors is the type of imaging technology the projector uses. Most tend to have either LCD or DLP chips and it is worth noting that the ANSI lumen measurement on a DLP projection will be higher when compared to and LCD projection of similar perceived brightness. This is due to the fact that the measurements are taken when projecting white light and DLP projectors are better at projecting white light than LCD. Of course not many people want to only project white light so it turns out that the ‘ansi standard’ isn’t actually very standard or that helpful.

You may think that so far it’s all a bit confusing and are asking yourself ‘how on earth can I chose between different ansi lumen projectors?’. The good news is that you needn’t worry about that right now. The bad news, there are far more important things to think about!

The things that will have the greatest affect on how bright your projected image looks are; 1) the size of the projected image, and 2) the amount of ambient light in the room.

inverse square law

If you have used a projector before you will notice that as you move the projector further away from the projection surface or screen the image not only gets bigger but it also gets dimmer. That is because you are spreading the same amount of light over a larger area. This is where something called The Inverse Square Law comes into effect and means that if you double the size of the image you need four times more light output to maintain the perceived image brightness. Similarly if you make the image three times the size you will need nine times the amount of light and so on. So the difference between having a 4ft wide image and 8ft wide image could be changing from a 1500 ansi lumen to a 6000 ansi lumen projector.

 

classroom-style-seminar-projectorIf you think that sounds daunting it becomes inconsequential when you factor in the effects of ambient light that can be anything from a desk lamp in the corner of the room to light streaming in through the window on a summers day. When it comes to dealing brightness Mother Nature holds all the cards. Thankfully in most situations you have some control over this. You can turn off the lights, close blinds and if necessary sit in relative darkness if you want to maximise the perceived brightness and contrast of the projected image. It sounds obvious but you would be surprised how many enquiries we get from people who want to project outdoors during daylight hours! Another popular one is the wedding dinner that is being held in a marquee and the Best Man wants to hire a projector to show some PowerPoint slides with pictures of the Groom. There is a massive amount of ambient light in a white lined marquee in summer and the sort of projection required to combat that isn’t usually within the means of the Best Man.

So the bottom line is that the choice of brightness is going to be determined by the size of your image (how big the screen should be is a separate conversation!) and the amount of ambient light or your ability to control the ambient light.

One last thought is that brightness is very much about perception. I doubt that anyone in your audience is going to get out a light meter and measure the brightness! How bright it looks to the audience is going to be relative to what they are used to, what they expect and relative to any other screens that they can see. What’s important is that the screen clearly communicates the words and pictures you need it to and there’s far more to that than just brightness but that’s for another day.

If you have read the above I have to congratulate you. You probably just wanted a quick answer but hopefully you have a better understanding of the factors involved. As a reward here is a rough guide for LCD projectors in the most common situations.

 

Projector Usage Projection screen width Projector brightness
(ansi lumen)
Small meeting room 4-5ft (1.2–1.5m) 1500-2500
Board room, large meeting room or classroom 5-6ft (1.5-1.8m) 1500-2500
Small Conference room 6-8ft (1.8–2.5m) 3500-5000
Small lecture theatre or conference room 8-10ft (2.5-3m) 5000-6500
Large lecture theatre  10-12ft (3-3.5m) 6500-10,000

 

As I write the above it is interesting to note that I remember that years ago we would use a 2000 ansi lumen projector on a 12ft rear projection screen. In those days 2000 ansi was pretty high-end and about as good as you could get. I recall that there wasn’t a problem seeing the image but the audience would have been sitting in relative darkness and it was always a nightmare trying to prevent spill from the stage lights washing out the screen. In todays world that simply wouldn’t cut the mustard and that’s what I mean about audiences expectation and relative perception.

image: inverse-square law: light. Art. Britannica Online for Kids. Web. 6 Feb. 2015

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