Lighting is one of the first things people need solar for. In early solar homes and farms in the depression, they had all DC lighting. Then came AC power from inverters in the 80s, but many still relied on DC for much of their lighting. Now in the 21st century though, we recommend mostly standard AC wiring for the house. A couple of DC circuits for emergency & maintenance are still a good idea. These can be LED path lighting, accent rope lighting, 12v Halogen track lighting, & always a DC bulb in the equipment room in case the inverter shuts off.

AC is the best choice for lighting now, because of the availability of reliable, low cost compact fluorescents. Standard AC wiring & switches are far cheaper than DC's heavy copper and special switches. The efficiency and savings of AC wiring and fluorescent outweighs the extra losses of the inverter.

AC (120v) can go 10 times as far as 12 v DC on the same gauge wire. Also, because the current is 10 times less (for the same power), you can put much more lighting on a smaller wire too.

AC Vs DC lighting

Comparing types of bulbs

Light output shows how much light each bulb puts out for the same power usage. LEDs can be almost 20 times more efficient than a regular bulb. Fluorescent could stay on 4 times as long for the same energy use.

Fluorescents are the best overall choice for most lighting. They come in regular long tube fixtures, Traditional Tubes come in 18", 24", & 48" sizes. Ballasts are still noisy magnetic. We sell DC electronic ballasts for the tube fluorscents.
Compact fluorescents are now available that are the same size and shape as regular incandescent bulbs. They fit most lamps & fixtures. Compact fluorescents are usually instant start with electronic ballasts, and have good color. We normally don't recommend DC Compact Fluorescents because they have not proven reliable -- they overheat at low voltage (a Low Voltage Disconnect is a must).
Halogen bulbs are best for viewing art work ,etc. where color is most important. 12 volt DC and 120 V bulbs and fixtures are available.
LEDs aren't in wider usage because its expensive to string enough bulbs together to light a room completely. Also, colors are very distorted under LED. For path lighting, flashlights, etc. they're the best.
Incandescent bulbs are one of the worst things you can have in a solar powered house (next to a toaster oven that won't turn off). They're only 5% efficient (95% of the energy they use is given off as heat), and there are much better alternatives

Final Recommendations:

We recommend mostly all AC lighting except for one emergency DC lighting circuit. Also, we recommend using mostly compact fluorescent lights, but mixing a few halogens in for spot lighting of certain areas. Regular incandescents are not recommended, and LED lights are great for flashlights, path lighting, and the emergency DC circuit.

Installation & Maintenance Tips:

Convert old DC lighting circuits to AC on older solar systems. We change all outlets on that circuit to AC and then pull the wires out of the DC fuse box, and rewire them (with extensions and a j-box, if needed) into the AC breaker box. Just make sure all the outlets are properly grounded, are converted to AC receptacles, and that no DC appliances could be accidentally plugged into the AC circuit.

Tips for Wiring for DC:

1) always check wire sizing. For example: you can't go more than 10 to 15 ft on regular 12 ga wire for 100 watts of lights. (See wire sizing tables or our handy wire sizer spread sheet)

2) Don't put more than 4 light fixtures per circuit.

3) Use DC rated switches. Old "snap" switches are DC rated, although they don't always say so. Silent switches usually say "AC only". Don't use them for DC!

4) Use DC rated fuses or breakers too. If they're not DC rated, like switches, breakers can burn in the "ON" position. If they're is an electrical danger, you may not be able to turn the switch off and the breaker may burn "on" too!

5) Watch those connections. Matching large (#2) wire to a light switch takes some specialty connectors. (See wire & connectors page) Switches can't handle wire bigger than 12 Ga., so run a short piece of 12 GA wire (pigtail ) to the switch itself.

6) Use our DC only outlets, so only the fixtures made for DC can be plugged into DC and vice versa.

7) Label DC light fixtures, so your house guest doesn't screw a 12 volt bulb into a 120 v circuit. (It's dangerous)