sleep mode and standby mode ..

Hello guys ,,

I'm working on an Arduino project , the problem is that my system consumes around 250 mA ( Sensors + Uno+ other components ) in operation status where the feeding power problem emerges in this case .
In the project I'm using 3 different sensors ( 2 with high current consumption ) + other components . The work principle of the system is that the second and third sensors should not start measuring until a specific value is gained by the first sensor . I'm looking to an effective way to reduce the power consumed as the system should be portable .

Some guys in the forum guide me to a sleep mode or a standby mode . As a beginner in a arduino , I need to know what these modes are ? ,are they effective in my system?, and How much reduction is expected in consumption current by these mode ?

I'm looking to an effective way to reduce the power consumed as the system should be portable .

Usually you turn the unneeded sensor off until they will be used. If they have a high current consumption you might use transistors or MOSFETs to switch power. Many sensor also support sleep modes.

Are the exact types of sensors a secret?

Some guys in the forum guide me to a sleep mode or a standby mode .I need to know what these modes are ?

They are listed in the datasheet of your MCU.

are they effective in my system?

They will reduce the current consumption of the MCU but might have drawbacks (no reaction to sensor events, delay while waking up, etc.). How effective they are depends on the complete system and you haven't told us the other components yet.

How much reduction is expected in consumption current by these mode ?

Nick Gammon has a good overview of the different savings.