Daylight Saving Shift
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From: Lew on 1 Nov 2009 21:33 Arne Vajhøj wrote: > Lew wrote: >> Arved Sandstrom wrote: >>> Just as for the rules for magnetic declination, I don't even try to >>> remember any of that. It's easy enough to work out from first >>> principles and local knowledge. For example, if you know that DST is >>> intended to give you more hours of light in the evening, that >>> immediately tells you in what direction the clock must go. >> >> The irony is that Daylight Savings does not give you more hours of >> light in the evening. It just makes people go to (and thus leave) >> work an hour earlier. The evening itself still has the same number of >> hours of light. > > Not if the evening starts when you are home from work. Then when the evening starts depends on what job you do. A farmer's evening starts at full dark by that definition. Doesn't it make more sense to define evening in terms of where the sun is than what one's profession is? I define evening as when the sun is close to setting, i.e., when the light begins to fade. It's a fuzzy concept, of course, but utterly not dependent on what the clock says. I define afternoon as when sun passes its zenith. I find other definitions stupid, as indeed I find the whole concept of Daylight Savings Time. Ptui! I spit on the practice! -- Lew
From: Lew on 1 Nov 2009 22:28 Roedy Green wrote: >> Maybe we will see DST creep till it totally takes over. Arne Vajhøj wrote: > The politicians make that decision. > > We just need to write the software to match those decisions. > > Note that even if DST changes were completely removed, then we > would still need to support it due to historical data. I would favor abolishing DST altogether. If that means leaving the clock set ahead of historic Standard Time settings, so be it, although the last time that was tried in the U.S. (in the 1970s) it was a failure. People objected to the children having to wait for morning school buses in the dark, among other things. The subject is politically controversial. Some claim energy savings due to the use of DST. AFAIK there's no hard evidence to support this, at least, not that takes into account the increase in costs due to air conditioning and morning lighting. Certainly there are lots of claims that DST saves energy, but for some reason no one ever seems to cite studies or methodologies to support those claims. There is a vocal but politically disadvantaged contingent that denies the validity of those claims. But our infinitely wise and benevolent governments say that it must be so, though somehow jurisdictions that don't use DST don't seem to suffer unduly thereby. As Arne points out, dates are a matter of socio-political mandate and our software simply must reflect the reality. -- Lew
From: Thomas Pornin on 1 Nov 2009 22:43 According to Roedy Green <see_website(a)mindprod.com.invalid>: > I see no advantage in losing an hour of evening daylight in November. Historically it is the other way round: DST is a special time shift applied during summer. Thus, DST does not remove an hour of evening daylight in November; rather, it adds an hour of evening daylight in March. --Thomas Pornin
From: Joshua Cranmer on 1 Nov 2009 23:31 On 11/01/2009 10:28 PM, Lew wrote: > The subject is politically controversial. Some claim energy savings due > to the use of DST. AFAIK there's no hard evidence to support this, at > least, not that takes into account the increase in costs due to air > conditioning and morning lighting. Certainly there are lots of claims > that DST saves energy, but for some reason no one ever seems to cite > studies or methodologies to support those claims. There is a vocal but > politically disadvantaged contingent that denies the validity of those > claims. The recent research summaries I've seen all seem to indicate that the impact of DST on energy use is somewhere around ±0.2% (it's a number that's rarely put into full context, so I'm not exactly sure what the percentage is of--probably average daily summer energy usage). The sign is naturally hotly debated in political circles whenever tweaking DST is bandied about. *Performs some searching to find research papers* The literature review I just finished reading seems to suggest that most of the conclusions about the energy-saving nature of DST were formulated about 25 years ago, when lighting in particular was much less efficient than now (the hypothetical best-case scenario for energy savings would be equivalent to replacing about 15% of your incandescent light bulbs with compact fluorescents) and also fails to take into account the modern shifts in habits. Its primary conclusion was "the stuff out there sucks, we need modern comprehensive research on this topic." Other papers recently published seem to suggest that DST may no longer be saving energy. That may just be a manifestation of confirmation or perhaps publication bias--I'd expect that people finding energy savings due to DST would be less likely to publish their results nowadays. I'm also not a big fan of DST myself. Oh well, if humanity ever discovers interplanetary or even interstellar travel (as well as sufficiently speedy communication to make chronological synchronization across disparate settlements necessary), the mess resulting from DST will be the least of our worries. -- Beware of bugs in the above code; I have only proved it correct, not tried it. -- Donald E. Knuth
From: Morris Keesan on 2 Nov 2009 00:52
On Sun, 01 Nov 2009 22:43:44 -0500, Thomas Pornin <pornin(a)bolet.org> wrote: > According to Roedy Green <see_website(a)mindprod.com.invalid>: >> I see no advantage in losing an hour of evening daylight in November. > > Historically it is the other way round: DST is a special time shift > applied during summer. Thus, DST does not remove an hour of evening > daylight in November; rather, it adds an hour of evening daylight in > March. Rather, it removes an hour of morning daylight in March, which doesn't get restored until November. -- Morris Keesan -- mkeesan(a)post.harvard.edu |