So far, I’m very anxious to see how much power I can save with my laptop (let’s say – if I turn of my screen, my speaker, my ODD, etc). Well, this time I have chance to test myself 
I use my laptop, ASUS F3JC. Powered with Intel T7400 (2.16 GHz), 2 GB or RAM, 120GB of SATA HDD, 15.4″ screen, and a Super Multi ODD. What else? I use standard 65 Watt adapter.
I use a device that can measure the power consumption directly. You just need to plug this device on to the wall outlet, then connect your peripheral to this device. Then, this device can measure the power consumption of your peripheral instantly (real time). Take a look of the device below.
This tiny little device can measure the Voltage, Current, Power Consumption (in Watt or VA), Frequency (Hz), Efficiency (Power Factor), and Power Usage (kWh). This is a great device, but somewhere not available in Indonesia.
And here is the result:
With minimum brightness (one step before completely off), I get 21 Watt of power consumption (with processor clocked at 994 MHz). Additional 2 Watt is needed if I set my processor at 2160 MHz. With full load (2 core all at 100%), my notebook will consume around 28 Watt (at 994 MHz) and 56 Watt (at 2160 MHz).
With medium brightness (half step between completely off and maximum setting), I get 23 Watt of power consumption (with processor clocked at 994 MHz). Similar with the result before, additional 2 Watt is needed if I set my processor at 2160 MHz. With full load (2 core all at 100%), my notebook will consume around 30 Watt (at 994 MHz) and 58 Watt (at 2160 MHz).
With maximum brightness (maximum brightness setting available), I get 26 Watt of power consumption (with processor clocked at 994 MHz). A little bit higher, I need additional 3 Watt if I set my processor at 2160 MHz. With full load (2 core all at 100%), my notebook will consume around 34 Watt (at 994 MHz) and 61 Watt (at 2160 MHz). I also test with single core only (100% load on first core, and idle on second core). The result has no different in significant margin I think. I will use around 33 Watt vs 34 Watt in 994 MHz and 54 Watt vs 61 Watt in 2160 MHz. I think this is because the second core is not totally shut-off physically, only not used at its maximum load.
Additional test:
- Speaker at maximum volume will consume around 1 Watt
- WLAN will consume around 1 Watt
- Spin-up CD/DVD will consume around 3 Watt
- Reading CD/DVD will consume around 6 Watt
Conclusion:
Well, from this short article, you can see that actually, the back light of the screen will not consume too many power as we have thought before (please remember that I’m currently using 15.4″ screen, it will consume less power for smaller screen).
If we can do some math, with minimum back light (full processing power) will consume around 56 Watt, while it will consume around 61 Watt with full brightness. The 5 Watt different means around 10% only. So if your battery should last 4 hours, with maximum brightness, it will last around 3,6 hours (or around 3,8 hours with medium brightness). A price that you have to pay for a comfortable screen?
WLAN and speaker will not consume a lot of power, but reading (or writing CD/DVD) simply will. Even the spin-up process (after you insert a CD/DVD in to the drive), will consume around 3 Watt of power.