Science > Physics > Your opinion, please, on a legal phrase as it relates to lighting.
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Science > Physics |
| User: |
"Chuck" |
| Date: |
21 Jan 2005 06:32:34 AM |
| Object: |
Your opinion, please, on a legal phrase as it relates to lighting. |
I came across a state's vehicle code that states (partially): "... this
section applies to the color of lamps and to any reflector exhibiting or
reflecting perceptible light of 0.5 candela or more per foot-candle of
incident illumination."
I have a degree in physics and I find this statement vague at best and
confusing at least in its legal jargon posing as some sort of physical
lighting standard. I believe the phrase means nothing, when using the
current definition of a candela. I would like to have some other opinions
on this, if at all possible.
Thanks in advance.
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| User: "CWatters" |
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| Title: Re: Your opinion, please, on a legal phrase as it relates to lighting. |
21 Jan 2005 12:56:07 PM |
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"Chuck" <ssmith25nospam.furme@nc.rr.com> wrote in message
news:CD6Id.8686$K72.1643842@twister.southeast.rr.com...
I came across a state's vehicle code that states (partially): "... this
section applies to the color of lamps and to any reflector exhibiting or
reflecting perceptible light of 0.5 candela or more per foot-candle of
incident illumination."
If I remember all this correctly....
The only real problem is the mix of SI and Imperial units. Fixing that and
it says...
"light of more than 0.5 candela or more per 10.76 lux of incident
illumination"
I believe they use Candela as the units for the light reflected (and not
Lux) because the reflecting surface could have a focusing effect.
A plane mirror would absorb a percentage and reflect a percentage of the
light (eg it has an "efficiency" the units of which are dimensionless). A
curved mirror on the other hand could change the "density" (=intensity) of
the light as well which is why I think Candela is used.
but I may be wrong!
Colin
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| User: "Androcles" |
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| Title: Re: Your opinion, please, on a legal phrase as it relates to lighting. |
21 Jan 2005 06:57:11 AM |
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"Chuck" <ssmith25nospam.furme@nc.rr.com> wrote in message
news:CD6Id.8686$K72.1643842@twister.southeast.rr.com...
I came across a state's vehicle code that states (partially): "...
this section applies to the color of lamps and to any reflector
exhibiting or reflecting perceptible light of 0.5 candela or more per
foot-candle of incident illumination."
I have a degree in physics and I find this statement vague at best and
confusing at least in its legal jargon posing as some sort of physical
lighting standard. I believe the phrase means nothing, when using the
current definition of a candela. I would like to have some other
opinions on this, if at all possible.
Thanks in advance.
The usual interpretation is that the definition applies at the time when
the law was passed, and doesn't apply to any later definition.
There is ample precedent. For example, as late as 1946 a charge of
witchcraft was successfully brought in London against a woman claiming
to have clairvoyant powers, a conviction obtained which resulted in a 6
month jail sentence.. That law has since been rescinded, but was still
current at the time of conviction. Laws tend to be modified only when
acted upon.
Androcles.
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| User: "tj Frazir" |
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| Title: Re: Your opinion, please, on a legal phrase as it relates tolighting. |
21 Jan 2005 09:51:51 AM |
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YOU have a degree =BF
in physics ?
and you dont understand candlepower .
What fuckin mail fraud flunkie sent you a deploma ?
You gota PHD dumbass ,,
show me the math then moron.
I gota PHD .
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| User: "Sam Wormley" |
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| Title: Re: Your opinion, please, on a legal phrase as it relates to lighting. |
21 Jan 2005 03:54:01 PM |
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Chuck wrote:
I came across a state's vehicle code that states (partially): "... this
section applies to the color of lamps and to any reflector exhibiting or
reflecting perceptible light of 0.5 candela or more per foot-candle of
incident illumination."
I have a degree in physics and I find this statement vague at best and
confusing at least in its legal jargon posing as some sort of physical
lighting standard. I believe the phrase means nothing, when using the
current definition of a candela. I would like to have some other opinions
on this, if at all possible.
Thanks in advance.
The primary SI unit for Luminance is one candela per square meter [cd/m^2] whereas
the primary SI unit for Illuminance is the lux (one candela steradian per square
meter) [cd.sr/m^2].
The primary SI unit for Luminous Intensity is the candela [cd] and
the primary SI unit for Luminous Flux is the lumen [cd.sr].
UNITS AND CONVERSION CHARTS
A Handbook for Engineers and Scientists
by Theodore Wildi
IEEE Press, New York 1991
IEEE Order Number: PP0267-5
ISBN 0-87942-273-4
As systems of measurement evolved in various parts of the world, they
produced a large number of units. Theodore Wildi's handbook shows in an
exceptionally clear and useful way how these units relate to each
other, and how they are defined. Its principal advantage lies in the
conversion of units, a process made exceedingly simple by a set of new
conversion charts. They enable the engineer, scientist and technician
to make rapid and clear-cut conversions between units of the American
Customary system, the English system, former metric systems, and the
International System of Units (SI).
The conversion charts rank the units by order of size so that the
relationship between any two units can be found quickly and without
ambiguity. They significantly reduce the time usually needed to consult
handbooks, tables and so forth, in solving engineering and scientific
problems. The units of various quantities such as force, pressure,
viscosity, etc., are displayed by means of conversion charts. The
charts show the relative size of the unit by the position it occupies
on the page. The largest unit is at the top, the smallest at the bottom
and intermediate units are ranked in between.
SI units and their multiples and sub-multiples appear in red (gray as
reproduced here) boxes on the conversion charts. Because they are
connected by flyers ("flyers" are introduced to bypass a series of
units) that are multiples of ten, it is possible to move swiftly from
one end of the chart to the other should a conversion between
widely-separated units be required. Exact conversion numbers are in
red, the remaining black numbers are accurate to the number of
significant figures shown. The conversion rule is simple - with the
arrow, multiply - against the arrow - divide. For example a parsec
equals 3.2616 light years.
The charts are based on values published by the American National
Standards Institute (ANSI), the International Organization for
Standardization (ISO), the Bureau International des Poids et Mesres,
The Committee on Data for Science and Technology (CODATA) and by the
Institute of Electrical and Electronic Engineers, Inc.(IEEE). Because
the charts are universal, conversions can be made quickly and
confidently. Official symbols for all SI units are given, along with
the name of the unit. For dimensional analysis, the charts show the
dimensions of units in terms of SI base units (shown in brackets).
In addition, five appendices contain useful information on units,
including: an overview of the International System of Units; the
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interpretation of decibel measurements; selected physical constants;
the application of quantity equations and numerical equations in
solving technical problems.
.
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