How does ambient light affect the selection of a process monitor?
Process monitors which must be readable in direct sunlight should use LCD displays, while indoor applications can usually take advantage of an LED display's superior legibility. Outdoor applications that must also be viewable at night, or in dimly lit areas, should use locally-powered process monitors with backlit LCD displays.
At the present time, high-intensity LED's can not be illuminated adequately with currents much below 60mA. Therefore, if display legibility is an important requirement, locally-powered LED display process monitors are the better choice for indoor applications since their power consumption is not limited to the 4-20mA currents circulating in the loop.