Key Points:

The Government has decided to extend daylight saving from next year for reasons that are spurious at best. I am not aware that there has been a huge clamour from busy commuters for early-evening barbecues in April and September. It's a nice idea to think of April as summer, but it's a delusion.

Children will not benefit much from extra evening daylight in March and April. And it's hard to see how more darkness in the morning, when it's cold, is going to save on electricity and other forms of energy.

I teach an economics class at 8.30am two mornings a week. Before that I have to take my son to primary school.

The last weeks before the April holiday are particularly important learning weeks for my students and for my son. In late March my students must sit a 90-minute test at 8.30am. It will do them no favours if the sun doesn't rise until 7.30 am.

In 2008, daylight saving will end on April 6. Consulting the Herald's Sun, Moon and Tide tables for 2007, the sun rose on April 6 at 6.38am; that's 7.38am with daylight "saving".

Compare that with the winter solstice, June 22, which has a sunrise at 7.34am. Yes, the sun will rise later in our "extended summer" than it will in the middle of winter.

Sunset on April 6 (Easter Saturday this year) occurred at 6.10pm. It would be 7.10pm with daylight saving. That's basically the evening meal time. It's hard to see that many of us will use that hour - between 6pm and 7pm - any differently whether we have daylight saving or not.

The problem won't be so bad in late September. A 6am sunrise will become 7am, an acceptable time for primary school children to wake up. While it's not clear that an extra hour of daylight in the late September evening is more valuable to most of us than it is in the morning, the real problems will occur in late March and early April.

Let's consider four issues that relate to the use of time at the beginning and end of the day: school children's activities, commuting, energy use and recreation.

Children seem to synchronise pretty well with the sun. That's okay in the summer holidays because they can sleep in in the mornings if they need to. In late March children will come inside at around 6pm, whether or not the sun is about to set, but will tend to go to bed later if there is extended evening daylight.

Is it not good for educational outcomes if we have to wake children on dark and often cold mornings in late March and early April. The darkness just compresses the early-morning rush.

Young children will be more likely to be driven to school instead of walking, more likely to be late for school, and more likely to be unsettled and tired at school.

More dark mornings will have a bigger impact on commuters than will more daylight after 6.30pm.

More cold vehicles with condensation. More driving in fog. More tired and stressed drivers. More people leaving their car lights on when they arrive at work. More carbon emissions.

Driving colder vehicles in darker and colder conditions will add to our fuel bill. So will more home heating in the mornings. There will also be a greater risk on dark mornings that appliances such as heaters and stoves will be left on all day.

Energy use in the evening in April is much less related to darkness and coldness than it is in the morning. Rather it's about cooking the evening meal.

Finally, recreation. We are told to exercise more. What's the best time of day for busy adults to exercise? Yes, it's early in the morning, between 6 and 7am.

So how much exercise will be lost by introducing an additional hour of darkness in the morning? And what will be the cost to our healthcare facilities of reduced morning exercise by both adults and children?

Common sense tells us that June mornings should be darker than April mornings. It tells us that mid-March is a good time to reset the clocks, always before Easter.

Morning daylight in March and April is too valuable to lose.

Being able to eat dinner and watch the TV news in autumnal daylight for two extra weeks is not compensation enough.

* Keith Rankin teaches at the Unitec Business School in Auckland.