I am not an electrician but I would say the 0.5mm wire is a bit fine for what we need. The wire I used is around 1.3mm so 1.5mm in the wire you linked too should be OK.would 13 core irrigation wiring do the job?
http://www.brightonirrigation.com.au/category55_1.htm
http://aquatrad.com.au/products.htm...e=flypage.tpl&product_id=1050&category_id=253
The LED's draw a fair bit more current than a solenoid :)