Read the passage below carefully, and then choose the best answer:
The LED Lighting Revolution
If you have picked up any electronics magazines recently, you have probably heard about LEDs; yet chances are, you probably don’t realize why they are so special. The truth is that these tiny light bulbs are helping to improve watches, remote controls, televisions, and a host of other projects. Diodes are components that enable energy to flow in one direction, while simultaneously blocking the current from the opposite direction. This is similar to how a valve works on a faucet. If electronic manufacturers require currents to flow in several directions, then multiple diodes will be included in the circuit design. With LEDs, every time a current passes through them, a light is emitted. LED is short for light-emitting diode. Although they have only recently waves in the past decade or so, early models have been around since 1962. There are several benefits that LEDs offer when compared to incandescent or fluorescent lighting. For starters, they have extremely long-life spans in the range of l00,000 hours even in the toughest conditions. They also require far less energy than power sources, which can save users money over the long run. Since LEDs don’t contain moving parts like other bulbs, they can withstand heavy impacts without getting damaged. Finally, they don’t require any _warm-up time_ so they instantly light up when switched on. The only drawback is that they are still a more expensive to purchase at the moment. LEDs were first used on digital clocks, but they have come a long way since then. They have certainly done a lot to improve TV technology. LED TVs have been a hit because they can be built extremely thin, yet also offer power-saving benefits. LED TVs also provide a wider range of colour, which allows for more lifelike and vivid images. In the future, organic LEDs, or OLEDs, will bring additional benefits for viewers. OLEDs are even more flexible than LEDs, so manufacturers will be able to create bent display screens and lights. Therefore, you will be able to roll up your living room TV set and pack it in your suitcase. In other words, LED and OLED technology will likely be lighting up your life for years to come.
4. The word “_this_” in paragraph 2 refers to ________
