This is a known fact that CRT monitors take more power as compared to the LCDs.
If you have a CRT monitor, the big monitor with the bloated tail and a few KGs weight, you are consuming the most power. The power consumption of a CRT monitor ranges from 100watts to 300 watts depending on the size, model and make of the monitor. Typically, the older models used to consume more power and newer ones are better in terms of power consumption.
If you have a flatter variant of a screen that could be a TFT, LCD, LED or Plasma screen, you are using less power as compared to the CRT monitors. Most of the laptops, hand held devices like pdas and mobile phones are using this kind of displays these days. If you are using LCD, TFT or LED monitor for your computer as external display, your typical power consumption is somewhere between 50 watts to 200 watts depending on the size. For example this 15” LCD I have consumes 55 watts. There can be screens that take even less power.
This worksheet provides a more quantitative way of calculating your poswer consumption depending on different monitors you are using.
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