In Part III we discussed the different methods of creating images for projection. In this post we will go over the different light sources.
None of the imaging technologies would be possible without a light source. Brightness in projection is often referred to in ANSI (American National Standards Institute) lumens. It is important to be sure that the rating you are looking at is referred to this way as it is a universal standard put out by a non-profit organization in order to provide an even playing field. Some manufacturers will skirt this definition from time to time in an effort to improve how the projector is perceived.
At present there are three different light sources being used. Manufacturers are using lamps of various types, LEDs, and Lasers. Lamps are obviously not new. There are a wide range of types, all of which emit heat, requiring cooling systems to maintain the equipment. The downside to lamps is that they will eventually fail. One method to combat this has been to have more than one lamp in a projector so that when one fails the other continues functioning, or can be turned on without going to the projector (usually automatically). Not losing the image for the audience is often the priority, so having another lamp in place is a big bonus, but using them both together can also increase the brightness of the projected image. When you are comparing projectors it is good to keep the lamp type in mind, and also look at how many hours it is expected to last, what kind of warranty does it have, and how much does it cost to replace. Depending on your use of a projector you may need to upgrade your technology before you need to replace an old lamp, but you also may have to spend more on the lamp than to replace the projector with current technology. The other downside to a lamp is that as it ages the color temperature tends to change and the brightness goes down. It is not uncommon for good rental houses to replace a lamp at half of its lamp life in order to maintain good quality for their customers. In this case they will usually retain the old lamp as a backup for emergencies.
LED (Light Emitting Diode) technology is another area that has advanced rapidly in recent years. LEDs are not new and have been in electronics for decades, used on displays to indicate simple things like the power being on or off. When the brightness was able to be increased they began being used in light fixtures and are now being employed as a light source for some projectors. There are three big advantages: the life expectancy on them is incredibly long, they produce very little heat and since multiple LEDs are clustered to achieve brightness, the amount of power needed is far less than with traditional lamps. This is still new to the market however, and is not highly proven in the projection industry. LED projectors often cost more than their counterparts and are used in smaller, less reliable projectors. To gain brightness, most manufacturers are combining this technology with Laser technology in a sort of hybrid, which is also a newer concept and yet unproven.
Laser technology in itself however is just as it sounds. Larger scale projection manufacturers have started to use three different colored lasers as light sources for producing brighter images. The lifespan of the source is virtually unlimited and the brightness is stellar, however the cost is often stellar as well.
So in summary, here are the common options for imaging technologies and light sources. These can be combined to generate various options by a manufacturer:
In the next post we will cover lens selection, and some purchasing advice.
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