Which PoE standard allows the least amount of power to be drawn?

The 802.3af standard, also known as Power over Ethernet (PoE), allows devices to draw up to 15.4 watts of power per port. This is the minimum power level set by the IEEE for PoE, specifically designed to power devices such as IP cameras, VoIP phones, and wireless access points which do not require high power levels.

This standard was created to meet simple power requirements while allowing for the convenience of using a single cable for both data and power, which can simplify installation and reduce cabling costs. It is tailored for low-power devices that can operate effectively within this limitation.

In contrast, other standards like 802.3at (PoE+) can provide higher power levels, up to 30 watts per port, and the 802.3bt (PoE++) can deliver even more power, going up to 60 watts or 100 watts depending on the implementation. Meanwhile, 802.3ah is not directly relevant to power delivery as it pertains to Ethernet in general without specifics regarding PoE capabilities.

Thus, 802.3af allowing the least amount of power makes it the correct choice.