How the core technology of a projector makes a drastic difference
Projectors as we know them today are in the beginning of one of the largest technology transitions since the first “portable” projector under 50lbs rolled out in 2007. With the advent of laser illumination, virtually every classroom, meeting room, and eventually home theater will transition to solid state lighting – making lamp based projectors about as attractive as a Nokia candy bar style cell phone.
One of the most important questions facing potential purchasers of laser projectors is what is the core technology being used to create the picture from the lasers. While laser projectors are available at many brightness and resolution levels, there are distinct differences between laser projectors based on DLP technology vs. traditional LCD technology used in projectors.
Impact of dust on a laser projector
Although laser light sources can last 20,000 hours or more – dust is a much larger concern on a laser projector than a traditional lamp projector. Because of the intense heat around a laser beam light source, a microscopic dust particle can be easily sucked into the high temperature low pressure area around the beam – causing it to burn up or become molten. This material can then deposit itself anywhere on the projector, including optical components such as lenses, laser diodes, or other critical components.
These small spots can not only block the light, but also become hotter than the other components, creating cooling problems. Therefore – keeping dust away from the laser components is critical to ensuring that a projector lasts as long as the laser light source.
DLP IP5X Sealed Engine vs. traditional LCD filters for dust control
BenQ introduced the first laser based education projector in 2012, we have learned many lessons from unique global markets such as Beijing, which is located near the Gobi Desert and suffers from a higher than normal amount of air pollution. While a filter is always the easiest way to try and protect a laser projector from dust, there is still a risk that the smaller particles will get into the chassis. If these small particles find their way to the laser engine, usually the image damage is permanent.
The obvious solution was to create a completely sealed optical engine. Because the DLP chip is sealed and “bounces” the light off the chip, it enables BenQ engineers to use heat pipes and other techniques to remove heat from the engine instead of having to blow air directly onto each device. Then a typical BenQ DLP laser engine is sealed at a dozen or so points to ensure projection from dust. Each engine is then certified with an IP5X rating by a third party testing agency to ensure its dust resistant capability. This enables a projector that does not need filters or filter cleaning, and with its third party certification, can be trusted by buyers to last.
By contrast, typical laser projectors using LCD have filters that need to be monitored and maintained. Some models have mechanisms that can blow dust off the filters at regular intervals (e.g. 100 hours) to reduce maintenance, while other models use temperature sensors to indicate when the filter needs to be cleaned. Cleaning projectors often require ladders or lifts to access them in classrooms and lecture halls.
Calculating the cost of filter cleaning using the CoSN TCO model
According to CoSN TCO guidelines, filter cleaning would be identifiable and recurring cost of ownership of any projector that has filters. Depending on its location, filter cleaning on some projectors may require rental of a power lift, ladders, and other equipment (e.g. special vacuums) to access and clean the projector. These costs, plus the fully loaded hourly or piece rate of the employee or contractor is used to calculate filter cleaning costs. To calculate the impact on total cost of ownership, you can reference the projector created by Texas Instruments using the CoSN TCO guidelines at www.dlp.com/tco.
Color Fading and Decay
Have you ever seen a yellowish image with an older projector? One of the symptoms of traditional LCD projectors suffering from this problem is that the blue looks green and white looks yellow. One common concern with color decay is that it often occurs after the projector has been used for a while and may not be covered by a warranty.
So does this change with laser projectors? Since laser projectors are relatively new, how can a buyer be sure there is no color decay on their newest projector, where the projector does not last as long as the light source? The answer lies with Texas Instruments DLP chip.
Because DLP chips create images by reflecting the light (instead of having the light pass through the device), and are based on semiconductor technology, projectors using DLP chips are virtually immune from color decay. This is especially critical in heavy usage applications such as Digital Cinema, where a DLP laser projector generates 60,000 lumens for up to 12 hours per day, seven days a week – over 3000 hours per year – without suffering color decay.
This is one reason BenQ only uses DLP chips in their corporate and education laser projectors to enable a long lasting projector life to its customers.
Contrast is an important element of a projected image, and an image with low contrast but the same lumens can be harder to read in a classroom, or be unable to display small details in an image. Unfortunately, contrast specifications used in projectors don’t help the process, since they only measure the difference between a full white image and a full black image, known as Full on/off. According to Projector Central, “Full On/Off is is the most meaningless and misleading spec …easy to manipulate, (and) it produces misleading numbers.”
The ANSI standard, not commonly specified in projector spec sheets, use black and white boxes that force a projector to show both dark and white images on the same screen at the same time. According to Projector Central, High ANSI contrast is characterized by solid blacks, brilliant whites, rich natural color saturation, well-defined shadow detail, and a deep three-dimensionality in the image. Low ANSI contrast has more anemic black levels, lower color saturation, muddy shadows, and a shallower, more two-dimensional image.
For a classroom projector, higher ANSI contrast is ideal for teaching, enabling black letters on a white background to be easier to see in a English or Math class, and can offer more details on a photo or diagram in science class. Since contrast specs on full on/off may be misleading, a simple test with ANSI contrast images can easily show the difference between LCD or DLP projectors when comparing them side by side.
At BenQ, we use our experience with DLP chips to generate the highest ANSI contrast possible for the user, rather than using tools such as an iris (which reduces the overall brightness) to improve the Full On/Off specification. Here is an example of two ultra short throw laser projectors, where the left side LCD projector has higher contrast specifications on the spec sheet, but lower ANSI contrast. The BenQ DLP projector on the right has lower contrast numbers on the spec sheet, but clearly higher ANSI contrast. Bottom line – a simple test with high contrast material is an easy way to validate the readability of a DLP or LCD classroom or conference room projector model.
In the past, color performance of projector models could vary dramatically. Some projectors focused on generating higher contrast for improved readability, while others delivered lower contrast but highly saturated colors. With laser projectors, it is now easier for projectors using either technology to create color accurate images that may differ from model to model but are generally color accurate.
The easiest way to measure color accuracy is to use existing color standards used in every other display device such as monitors, televisions, and digital cinema projectors. For monitors and televisions, the standard that all these devices use is sRGB, which defines how much blue, red, green, and secondary color coverage should be measured. The DCI-P3 (Digital Cinema Initiative) color standard introduced in 2007 for movie theaters is much wider than sRGB.
Since both laser projectors using DLP and LCD technologies are capable of achieving both color spaces, the difference in color performance will vary by each individual model. BenQ projectors often represent color accuracy as a percentage of a defined color space in its specification sheets, and is an easy way to ensure that all the colors represented in the image are rendered as close as possible to the original image.
Laser and other solid state light sources represent a significant advance in projection technology, but are not the only factor in choosing the best projector model for the application. With differences in filter maintenance, IP5X sealed engines, and the immunity from color decay, laser projectors based on established DLP technology have a number of advantages to the buyer. BenQ’s DLP projectors also typically offer higher ANSI contrast for crisp images, and deliver accurate color using established industry standards used in other display products.