Bluetooth Version 2.1 + EDR and Version 3.0 + HS (commonly referred to as "Classic Bluetooth technology") and Bluetooth low-energy technology have much in common: they are all low cost, short range, interoperable, robust wireless technologies operating in the license-free 2.4GHz Industrial, Scientific and Medical (ISM) RF band.
But there is one critical difference: Bluetooth low-energy technology was designed from the outset to be an "ultra-low power" (ULP) wireless technology whereas Classic Bluetooth technology forms a "low power" wireless connection.
Classic Bluetooth technology is a "connection oriented" radio with a fixed connection interval ideal for high activity connections like mobile phones linking with wireless headsets. In contrast, Bluetooth low-energy technology employs a variable connection interval that can be set from a few milliseconds to several seconds depending on the application. In addition, because it features a very rapid connection, Bluetooth low-energy technology can normally be in a "not connected" state (saving power) where the two ends of a link are aware of each other, but only link up when absolutely necessary and then for as short a time as possible.
The operational mode of Bluetooth low-energy technology ideally suits transmission of data from compact wireless sensors (exchanging data every half second) or other peripherals like remote controls where fully asynchronous communication can be used. These devices send low volumes of data (i.e. a few bytes) infrequently (for example, a few times per second to once every minute or more seldom).
A tale of two chips
There are two types of chips that together form Bluetooth low energy architecture: single mode and dual mode. A single mode device is a Bluetooth low energy-only chip that's brand new to the Bluetooth specification – it's the part of the technology optimized for ULP operation. Single mode chips can communicate with other single mode chips and dual-mode chips when the latter are using the Bluetooth low-energy technology part of their architecture to transmit and receive. (See figure 1.) Dual-Mode Chips will also have the capability of communication with Classic Bluetooth technology and other dual-mode chips using their conventional Bluetooth architecture.
Dual-Mode Chips will use the Bluetooth low energy part of their architecture to communicate with single mode devices (Click figure to open PDF of larger version.)
Dual-Mode Chips will be used anywhere a Classic Bluetooth chip is used today. The consequence is that cell phones, PCs, Personal Navigation Devices (PNDs) or other applications fitted with a dual-mode chip will be capable of communicating with all the legacy Classic Bluetooth devices already on the market as well as all future Bluetooth low energy devices. However, because they are required to perform Classic Bluetooth and Bluetooth low energy duties, dual-mode chips are not optimized for ULP operation to the same degree as single-mode devices.
Single-mode chips can operate for long periods (months or even years) from a coin cell battery such as a 3V, 220mAh CR2032. In contrast, Classic Bluetooth technology (and Bluetooth low energy dual mode devices) typically requires the capacity of at least two AAA cells (which have 10 to 12 times the capacity of a coin cell and much higher peak current tolerance), and often more, to power them for days or weeks at most (depending on the application). (Note: There are some highly specialized Classic Bluetooth applications that can run on batteries with a lower capacity than AAA cells.)