Where does PoE fit with VLC?
I have previously talked about Ethernet over power, also known as power line communications (PLC) and the fact that this is a complementary technology to VLC since it allows the communications backhaul to be carried over the existing lighting power circuits. Now I want to consider Power over Ethernet (PoE), a technology that has been around for a while but is growing in popularity. Ethernet cables, such as CAT5, are clearly designed to carry data, but there are PoE standards designed to allow them also to carry power. The idea being that low power Ethernet connected devices, such as VoIP phones, networked cameras etc. can have just a single connector and no additional power adapter is required.
PoE comes in a number of flavours. There are two IEEE standards; 802.3af and 802.3at which both use a spare pair of conductors to carry the power. The more common af standard can provide up to 15W of d.c. power rated at 44V, 350mA. The more recent at standard known as PoE+ provides up to 30W. There are a number of non-standard variants and Cisco’s recently announced universal PoE variant (UPOE) can carry up to 60W of power using two pairs of cables from a CAT5e or CAT6 cable.
So why not use PoE to power high efficiency LED lighting installations since now the power, voltage and current parameters are well matched to this application. It seems to me, not just feasible that PoE infrastructure could be utilised for lighting, control and communications within a building, but it also seems very sensible. We have ourselves demonstrated high speed data communications transmitted from an IP connected light bulb. A number of companies including NXP and Color Kinetics have demonstrated the control of lighting via PoE, so we just need to add lighting power to this mix. Of course there are practical issues such as the length of the cable runs and the voltage drop over this distance, but these are simply constraints and not show stoppers.
A large Ethernet switch with UPOE could be enough to power a whole office in the not too distant future. With up to 60 W per connection the lights can be centrally powered and controlled, VLC can provide high speed wireless communications and the same infrastructure also supplies all of the wired communications and energy efficient desk top power too. This is potentially a great fully integrated technology, well great until the fuse blows – so better add battery back-up to the standard!