From the following website
http://webexhibits.org/daylightsaving/b.html
Daylight Saving Time also saves energy. Studies done by the U.S. Department of Transportation show that Daylight Saving Time trims the entire country's electricity usage by a significant, but small amount, of about one percent each day with Daylight Saving Time. We save energy because we use less electricity for lighting and appliances. Similarly, In New Zealand, power companies have found that power usage decreases 3.5% when daylight saving starts. In the first week, peak evening consumption commonly drops around 5%.
Energy use and the demand for electricity for lighting our homes is directly connected to when we go to bed and when we get up. Bedtime for most of us is late evening through the year. When we go to bed, we turn off the lights and TV. In the average home, 25 percent of all the electricity we use is for lighting and small appliances, such as TVs, VCRs and stereos. A good percentage of energy consumed by lighting and appliances occurs in the evening when families are home. By moving the clock ahead one hour, we can cut the amount of electricity we consume each day.
In the summer, people who rise before the sun rises are using more energy in the morning than if DST was not in effect. However, although 70% of Americans rise before 7 am, this waste of energy from having less sunlight in the morning is more than offset by the savings of energy that results from more sunlight in the evening.
In the winter, the afternoon Daylight Saving Time advantage is offset for many people and businesses by the morning's need for more lighting. In spring and fall, the advantage is generally less than one hour. So, Daylight Saving Time saves energy for lighting in all seasons of the year, but it saves least during the four darkest months of winter (November, December, January and February) when the afternoon advantage can be offset by the need for lighting because of late sunrise.
Daylight Saving Time "makes" the sun "set" one hour later and therefore reduces the period between sunset and bedtime by one hour. This means that less electricity would be used for lighting and appliances late in the day.
We also use less electricity because we are home fewer hours during the "longer" days of spring and summer. Most people plan outdoor activities in the extra daylight hours. When we are not at home, we don't turn on the appliances and lights.
There is a public health benefit to Daylight Saving Time by decreasing traffic accidents. Several studies in the U.S. and Britain have found that the DST daylight shift reduces net traffic accidents and fatalities by close to one percent. An increase in the dark mornings is more than compensated for by a decrease in the evenings.