While much of the US is due to begin phasing out incandescent bulbs from 2012 onwards, California began a year early on January 1st.
The move means 100 W bulbs must be replaced with energy-saving fittings that do not consume more than 72 W of power.
However, householders are still allowed to use incandescent bulbs with lower power ratings, such as 40, 60 and 75 W.
These will not be phased out until 2014, according to the newswire.
Alternatives include LED lights, halogen bulbs and compact fluorescent lamps, many of which will fit existing light sockets.
In Europe, the phase-out of incandescent lamps began on September 1st 2009 and is scheduled to continue in yearly stages until 2016.
By that stage, the bulbs should have been eliminated for home usage, with the exception of any stocks already manufactured or sold.
