12V DC Safety Lighting

This project is based around the need for several types of lighting in our home. Safety lighting is designed to come on in specific locations in our home but, only when it is occupied. It will also only operate when the twilight sensor determines that it is dark outside. It is designed to be low level lighting (using very little power), to provide enough light to see by and negotiate hallways, corridors, etc. It will be supplemented by more powerful convenience lighting (triggered by sensors in our home) and the normal manual and automated lighting.

Design

The safety lighting power comes from our 12V battery bank, via the 12V monitoring module.

Control

The safety lighting power is controlled and switched by the Home Control System (HCS), which uses a Ethernet IO board to switch the power via a power transistor.

Wiring

We have define a standard for wiring and ducting in our home. This approach makes the installation easier, much tidier and also means it could be removed very quickly from our home if required. It also ensures separation of low voltage wiring and keeps it away from the mains wiring in our home.

Colour coded (pink) wiring is used to distribute the power to all of the safety lights. Because it is readily available in 100m rolls, we have used a 16/0.20mm, 0.5mm², 11amp 'thinwall' cable. At some points, the distribution network will split into a 'star network' and this will be achieved using a 6-way blade terminal and insulated blade connectors.

A common earth is distributed from the the battery bank, through ducting and runs to each light. This reduces the amount of wiring required and this common earth then works regardless of the functions each light is used for. All earth (-ve battery terminal) wiring is done using thick, black wire.

Lighting

It is envisaged that all of the safety lighting is using very low power LEDs, to reduce the current and thus the voltage drop across the wiring. The total lighting load is planned to be less than 10W.

Software

The 'Safety Lighting' is an object modelled in our Home Control System (HCS) as a static Java class. It maintains state in a local database.

Progress

This project is currently live. The Home Control System (HCS) USB output board and power transistor sections are working. The remaining work is now further installation of the wiring and connecting up the various LED lights.

Conclusions

Whilst not a major feature of our home, the safety lighting is a worthwhile and useful feature. It provides the confidence to negotiate doorways and stairs before any convenience lighting is activated. Safety lighting is also considered a subset of our emergency lighting.