To date, almost all of the commercial or prototype LED-based projectors have been "New Era" projectors. Basically, this means they haven’t been bright enough for mainstream business applications such as use in conference rooms. Pico-projectors and LED-based ultraportable projectors have been cool and are even starting to sell in significant volume. But if you wanted to put them in a well-lit conference room and show a PowerPoint to a group of 10, they just wouldn’t cut the mustard.

Matt Brennesholtz
Insight Media Analyst

This barrier seems to be crumbling, however, and at least one LED-based projector is being demonstrated at InfoComm this week with just over 1000 lumens of output. This projector was built by Coretronic, with a single-chip DLP imager from TI, LEDs from Luminus Devices and a LED driver board from Osram.

I had a chance to discuss this projector with Kurt Eckles from TI and Brian Bennett from Luminus. The projector consumes 300W total and is said to produce "just over 1000 lumens." The DLP imager is an XGA imager with a 0.7" diagonal and ±14° mirror tilt. Older DLP imagers used a ±12° tilt but the increased tilt angle gives a higher étendue, allowing more of the light from the LEDs to reach the imager. The projector used Luminus PT-121 red, green and blue LEDs. According to Bennett, these LEDs are identical to the PT-120 LEDs except for aspect ratio: the PT-121 LEDs are 4:3 and the PT-120 are 16:9. Both types have the same total active area, the same drive current (up to 30A pulsed or 16A CW) and the same package design. The LED aspect ratio is designed to match the imager aspect ratio, again to maximize light transfer from the LED to the DLP.

LED drivers are a surprisingly important part of high-performance DLP/LED projection systems. LED drivers can be quite simple, although no circuit to handle 90A for the 3 LEDs can ever be truly simple. On the other hand, simple drivers lead to modest performance. To maximize output and contrast and minimize color-breakup, quite sophisticated drive circuits are needed. For example, the Osram driver, described in detail in the November 2008 Large Display Report, not only switches the 30A for each of the 3 LEDs, it will switch the 30A in 1 microsecond. According to Eckles, the projector overlays red, green and blue illumination of the LEDs to produce a virtual white segment to increase total throughput. This feature is one that can be implemented with the Osram drive board. While I don’t like white segments in lamp-based projectors, the higher saturation of the LED primary colors compared to the colors produced with a lamp/color wheel combination may make a virtual white segment acceptable. I certainly have no complaints about the colors I saw on the screen at Infocomm.

The projector output of 1000 lumens from 300W is respectable but not outstanding. For example, a DLP-based ultraportable projector with a lamp can produce up to 2700 lumens from 260 watt power input, for over 10 lumens/watt. On the other hand, 1000 lumens is still a respectable amount of light, and was considered perfectly acceptable for conference room use for many years. In addition, because of the Helmholtz-Kohlrausch (H-K) effect, LED projectors appear to be about 25% brighter than a similar lamp-based projector with the same CIE lumen output. This has been known qualitatively for a while and was documented by a SID paper this year, paper 20.1 from National Central University in Taiwan and Delta Electronics. Therefore, the effective output of this projector was the same as a 1250 lumen lamp-based projector.

Coretronic, the projector manufacturer, has not announced any customers for this projector. As an ODM, Coretronic is not expected to release the projector under its own brand name. So we will need to wait until a Coretronic customer makes an announcement before we can find out the price and availability of this projector. Eckles and Bennett said TI and Luminus were ready to deliver their parts in volume when Coretronic was ready for them. From the outside, at least, the projector looked production-ready. I would like to see inside, but…

Incidentally, I think Luminus Devices is celebrating this week. In addition to the Coretronic projector, three other companies have announced PhlatLight-based projectors: LG Electronics, projectiondesign and BenQ. I have seen the LG and BenQ projectors and plan on seeing the projectiondesign one. Vivitek says it will soon ship its LED-based home theater projector for $15K and Planar and Christie have LED-based video cubes. We will hunt for more and report on all of them in the next issue of Large Display Report.