Bimetallic thermometer combines two metals with different linear expansion coefficients, and one end is fixed. When the temperature changes, the thermal expansion of the two metals is different, which drives the pointer to deflect to indicate the temperature. This is bimetallic sheet thermometer, as shown in the figure on the above page. The temperature measurement range is - 80 ~ 500C, which is suitable for temperature measurement when the accuracy requirement is not high in industry. As a temperature sensing element, bimetallic sheet can also be used for automatic temperature control.
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Monochromatic LEDs efficiently cover most of the visible spectrum. In terms of blue light, the external quantum efficiency of the nitride diode exceeds 65%. For red light, the efficiency of the phosphor diode is about 50%. Of course, so far, no high-efficiency monochromatic LED can cover the "yellow energy gap" near 560 nm.
Using previous experience in warm white light, the researchers successfully used the down-conversion to convert the blue LED wavelength to a single-color amber light with a wavelength of 595 nm with a color purity of 98.7%. Depending on the temperature, the external quantum efficiency of PC amber LEDs is around 30%-40%. The new PC amber LED is five times brighter than the amber LED made directly. The luminous flux reaches 70 lm at 350 mA.
These LUXEON Rebel PC amber LEDs are used in a wide range of applications. It can be used in yellow traffic lights or signal lights, and can also be used in car turn signals or building sign warning lights. They can also be used in consumer electronics, and their high efficiency also makes their prices less expensive. 
A few days ago, Philips Lumi leds (San Jose, Calif.) researchers developed a monochromatic photo-nitride diode closest to the yellow LED energy gap, a phosphor conversion (PC) amber developed by ReginaMu el ler-Mach and her colleagues. A color LED that is down-converted into longer wavelength light by adding blue light from an InGaN LED to produce a cool white or warm white light (issued from a blue LED) by adjusting different processes.