What is an energy efficient solution to 400 watt metal halide lights?

I'd recommend high bay LED lights. There are many types of fixtures to replace halilde lights. these will save you at least 60-70% of the energy used and they will last much longer as well.

Adding sky lights will help if feasible.

Some online resources are below, while they are more US centered, the information in general is applicable anywhere.

http://www.cree.com/ This is an LED manufacturer who actually provides many parts to

other companies Including Philips Osram,

http://www.ledcity.org/ This is a cooperatvie industry website that focuses on LED technology

http://www.lrc.rpi.edu/ This one evaluates all current technologies

A global vendor of many products is http://www.digikey.com/ They do carry numerous Cree materials Although some you may have to special order, you can download their catalog or search interactive online. A sample page is http://search.digikey.com/scripts/DkSearch/dksus.d...

Cree also has a list of vendors who carry their products too. They are also very helpful and customer service oriented.

While the LED arrays may not be cheap on the surface- once installed, if line current is clean enough, you only need dust them for the next 30 years.

If the line current is full of transient spikes, or RF, consider adding common mode line filters to the power going to the driver circuitry. If you choose to run them at straight DC- add ferrite cores to the power feeds to the LEDS themselves to quench transients and RF. The cores can be salvaged from old computer equipment.

zoo and maybe