Question: I have two lights from B&Q which are normally battery powered but can be powered by a transformer with a regulated output of 6 V, 0.5 A DC. I would like to set up the lights to be powered off the same transformer but don't know how to calculate the voltage and current the transformer would be required to output (in either series or parallel).

I'd also like to add a time delay switch to the circuit - would [this one](http://www.ebay.co.uk/itm/Danlers-Plated-3-Wire-Time-Lag-Switch-6A-Resistive-or-Fluorescent-TLSW-A20-/271266710463?pt=UK_DIY_Material_Electrical_Fittings_MJ&hash=item3f28c183bf) work?

Answer: 
So, when you are connecting two lights in series, the current stays the same, but the voltage sums - U = 6 + 6 = 12V; I= 0.5A.
For parallel, the voltage is same, but the current is doubled - U = 6V; I = 0.5 + 0.5 = 1A
To power your two lights connected in parallel, you need a 6 volt, 1 amp power supply,based on the information you supplied. However, since the lights are designed for battery power, I suspect that they actually need much less than 0.5A each, so you may be able to run them both from an 0.5A supply - if you have an ammeter, you could check the actual current draw of the lights to be sure...

The time switch you linked to appears to require 230V AC, since the spec. says it requires a neutral connection, so it won't work on your 6 V DC, but should work on the 230V input to the power supply.