Optical Sensors: Unsung Heroes of HDTV Power Efficiency

Television manufacturers face mounting pressure to improve the energy efficiency of TVs.

By Cliff Roth

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Video/Imaging DesignWire
(11/4/2011 3:00:18 PM)

Against the backdrop of huge anticipated gains in home lighting efficiency over the next few years due largely to the phasing out of traditional incandescent light bulbs, television manufacturers face mounting pressure to improve the energy efficiency of TVs.  A bill adopted in 2009 by the state of California mandated reduced power consumption for this year (2011) and even further reductions for 2013.

But unlike with lighting, where the newer technologies of compact fluorescent and LED bulbs are inherently more efficient, LCD and plasma TV screens are already using more efficient lighting technologies. Squeezing out additional energy savings becomes more challenging.

That’s where optical sensors come in. These inexpensive components measure the amount of ambient light (and sometimes the color of that light), enabling the TV to adjust its brightness accordingly. By dimming the screen at night when there’s no daylight present, fairly large energy savings become achievable.

Among several competing vendors in this space, TAOS — Texas Advanced Opto-Semiconductor — stands out as one of the more innovative. They’ve taken opto-semiconductors (a photodiode, or group of photodiodes, is at the heart of all these devices) to the next level, by adding intelligence. They offer optical sensors that can be readily integrated into modern HDTV systems via standard I2C interfaces, and whose spectral characteristics and other parameters have been tuned to meet the needs of TV and display manufacturers. Some of their products focused on the ALS market (ambient light sensing) can also distinguish between daylight and indoor light, to adjust a TV’s color temperature as well as brightness level.

Much of this technology is highlighted in a 2010 white paper TAOS offers, “Ambient Light Sensing in Green HDTVs”(click on English pdf).  What distinguishes TAOS’ product offerings for TV vendors is the inclusion of application-specific intelligence that essentially allows light sensing to exist within the TV’s design as a programmable module, rather than a circuit that must be created from scratch. For designers who prefer to roll their own circuitry, other vendors in the optical sensing space include Vishay, Avago, OSRAM, Omron, Honeywell and Fairchild.

TAOS has similarly distinguished itself in creating energy savings for the small screen, on smartphones and tablets, with intelligent ALS opto-sensors measuring as little as a 2mm square. There are no government regulations mandating efficiency here, but consumers are well aware that battery life on these devices is of critical importance. A manufacturer who can gain another half hour or hour of run time via clever display brightness management is a hero to consumers. Again making the humble optical sensor the unsung hero of today’s displays in their never-ending march towards greater energy efficiency.