Appliance Control: Making Things Do Stuff - Smart Home Automation with Linux and Raspberry Pi - page 10

It supports all the existing functionality of the LM10U but can also remember the last brightness setting, allowing
the light to be smoothly changed when it's first switched on, which helps increases the bulb life.

N The cheaper modules switch on at full brightness, so if you enjoy mood lighting, then this is a variant
worth considering.

Note

Furthermore, this is one of the few devices in this section that supports two-way X10 communication. This
means that you can send a message to the device asking for its current brightness state, and it is able to reply. This is
unavailable with most other devices, meaning that you (or more specifically, your controller device) must remember
the last message it sent, hoping it arrived, in order to emulate the querying of the lamp's state. And even this result
might be flawed if the brightness was changed locally. In most cases, however, this functionality is unnecessary
because you rarely want to know whether the light is on. If you're going to bed, then you're not interested is whether
the light is on or not, only whether you can switch it off. Unless you have a very large house, you can usually see a single
light on in an otherwise pitch-black house and therefore know whether you need to resend the “all units off ” message.
The downside of this device is that it costs around three times that of the LM10U. However, there is a midrange
product in the LW12 that features the same specification but without two-way communication.

DIN Rail Dimmer (LD11)
This is a (very) high-power module, capable of controlling devices up to 700W, and it is consequently suitable for
mains halogen as well as traditional mains lighting. Instead of being used in place of a switch (like the LWM11) or in
connection with the bulb (like the LM15EB), this device is remotely placed near the fuse box, with the LD11 output
cables running into the light directly. This is a switch terminal on the LD11 that allows the appliance to be switched
on and off, as if it were local. However, with four (potentially) long cable runs from the appliance to the LD11 (two for
power and two for control, as visible in Figure 1-5 ), its purpose isn't so obvious.

Figure 1-5. The LD11, 50 × 80 × 70mm