Local Daylight Time (LDT) FAQ

What is it? – A new smart clock that knows what time it should be. LDT minimizes seasonal sunrise time variation, eliminates the need for time zones and ends changing clocks twice a year.

Why is sunrise important? – It’s healthy. People have a biological clock that is set by exposure to daylight. Keeping a natural schedule reduces depression and sleep disorders.

Aren’t time zones necessary? – No. Time zones are a coarse division of the earth’s rotation, with one hour jumps at arbitrary boundaries. Local time changes continuously in every direction, not just east and west. The change is small, three to six seconds per mile is typical.

No spring forward, fall back? – Actually yes, but without the jet lag. Local Daylight Time adjusts to the changing sunrise time, gradually, by about one minute per day or less. You won’t notice.

So time changes every day and every where. Isn’t that confusing? – LDT is simpler than the Standard Time system. With a smart clock, all that matters is the location and the date. There is no need to keep track of complex boundaries or government rules about daylight saving clock changes.

Smart clock, do I need to buy one? – No, Local Daylight time is free, from the Internet or your cell phone. You might need a new wall clock or a smart alarm clock, but there’s an app for that.

Why hasn’t this been done before? – Technology wasn’t ready for it. Standard time was created by the railroads in 1847. Daylight Saving time began in 1918. Now with computers, cell phones, GPS and the Internet, a better kind of clock time is both possible and practical.

I drive 30 miles to work. How will I get there on time? – You can set your LDT clock to match the one your boss uses. It will only be a few minutes different, unlike many commutes that cross time zones.

How do I schedule a conference call? – When long distances are involved, the best way is by using UTC, Universal Coordinated Time. That is what Standard Time is based on, but without the time zone confusion. You can check others local time to see when they are awake, but make the call by UTC so there is no confusion. UTC is also good for flight schedules.

Doesn’t LDT replace UTC? – No. Two time systems are needed. Local Daylight Time is for local purposes, UTC is for global purposes. Standard Time is just UTC with offsets for time zones and Daylight Saving. Those offsets are no longer needed except for some government regulations.

So sunrise is at the same time every day? – Not exactly. Because the longest day gets longer at high latitudes, a fixed sunrise time isn’t possible. Above the arctic circle, sunrise may not happen for months. In London, a constant sunrise time would push sunset to be after 11:30 pm in the summer. So Local Daylight Time reduces sunrise variation but lets it vary more at higher latitudes.

So how much does sunrise time vary? – At the equator LDT makes sunrise exactly the same every day, adjusting by ten to twenty minutes during the year. In San Francisco (38° N), sunrise varies from average by less than half an hour, compared to more than one hour with Standard Time. The effect is similar to Daylight Saving time but the irritation of changing the clocks and the randomness of time zone placement are gone.


© Copyright Keith Thomas 2013