For a discussion of UNITS used in lighting (lumens, nits, foot-candles, etc) -- see end of this page.
GLARE: The 8th edition of the IESNA Lighting Handbook (1993) defines glare as the sensation produced by luminance within the visual field that is sufficiently greater than the luminance to which the eyes are adapted to cause annoyance, discomfort or loss of visual performance and visibility. It stands to reason, then, that any good outdoor lighting design will minimize glare. If the light source itself is more apparent than what it is illuminating, then you have bad lighting. -- from the Dark Sky Association homepages.
Light TRESPASS is light that is distributed where it is not wanted or needed. Street lighting, for example, should light just streets and sidewalks, not shine into second floor bedroom windows or illuminate rooftops. Also known as spill light, light trespass occurs whenever light shines beyond the intended target and onto adjacent properties. -- from the Dark Sky Association homepages.
UPLIGHT is, in the truest sense of the word, wasted light. Light that goes directly up into the night sky is "lost in space" and serves no useful purpose. Uplight is the bane of astronomers and the occasional stargazer because atmospheric scattering artificially brightens the night sky, making distant celestial light sources difficult or impossible to see. Uplight often results from light fixtures which also produce glare and light trespass. -- from the Dark Sky Association homepages.
And from NEMA: "FULL CUTOFF" fixtures are those that allow "no light at or above a horizontal plane located at the bottom of the luminaire" (lamp plus fixture). In any event, the idea is simple - aim the light where and when it is needed, and don't send the light upwards or across property lines.
"The sky, our common and universal heritage, is an integral part of the environment perceived by humanity. Humankind has always observed the sky either to interpret it or to understand the physical laws that govern the universe. This interest in astronomy has had profound implications for science, philosophy, religion, culture and our general conception of the universe". Proclamation of 2009 as International Year of Astronomy. UNESCO General Conference. Paris 2005.
“Persons belonging to future generations have the right to an uncontaminated and undamaged Earth, including pure skies; they are entitled to its enjoyment as the ground of human history of culture and social bonds that make each generation and individual a member of one human family.”
Universal Declaration of Human Rights for Future Generations. La Laguna,
1994. Website: STARLIGHT:
International Initiative in Defence of the Quality of the Night Sky as
Mankind’s Scientific, Cultural and Environmental Righs
0. Compilation of regional night sky photometry
HERE
1. Denver City and County implemented new building codes including updated lighting regs... details
available at website DENVERGOV.ORG and
search for Lighting Regulations
2. Useful links to Colorado city, county, state lighting regs:
Colorado IESNA and select
link to LIGHTING CODES, near end of left column.
Light TRESPASS and GLARE refer to unwanted and harmful lighting.
During 2001, the Colorado Legislature agreed and modified state law to address these issues: SECTION 2, ARTICLE 82 OF TITLE 24, COLORADO REVISED STATUES IS AMENDED BY THE ADDITION OF A NEW PART TO READ: PART 9, OUTDOOR LIGHTING FIXTURES.
Astronomers are NOT AGAINST SAFETY, but are very worried about destruction of the night sky by lighting that shines uselessly into the sky, wasting money and depriving everyone of their cosmic birthright, not to mention causing inferior sleep and melatonin disruption. Badly aimed light also produces trespass nuisance, and disabling glare -- especially for older people.
The simplest solution also saves money: add a shield on top of new lighting, to direct all of the light toward the ground where it is needed.
Also, the use of motion sensors and timers reduce the cost of lighting to only when it is really needed.
GLARE: The 8th edition of the IESNA Lighting Handbook (1993) defines glare as the sensation produced by luminance within the visual field that is sufficiently greater than the luminance to which the eyes are adapted to cause annoyance, discomfort or loss of visual performance and visibility. It stands to reason, then, that any good outdoor lighting design will minimize glare. If the light source itself is more apparent than what it is illuminating, then you have bad lighting.
Light TRESPASS is light that is distributed where it is not wanted or needed. Streetlighting, for example, should light streets and sidewalks, not shine into second floor bedroom windows or illuminate rooftops. Also known as spill light, light trespass occurs whenever light shines beyond the intended target and onto adjacent properties.
UPLIGHT is, in the truest sense of the word, wasted light. Light that goes directly up into the night sky is "lost in space" and serves no useful purpose. Uplight is the bane of astronomers and the occasional stargazer because atmospheric scattering artificially brightens the night sky, making distant celestial light sources difficult or impossible to see. Uplight often results from light fixtures which also produce glare and light trespass.
And from NEMA: FULL CUTOFF fixtures are those that allow "no light at or above a horizontal plane located at the bottom of the luminaire" (lamp plus fixture).
LUMINANCE: refers to the OUTPUT of a source. Often a "blackbody" or Planckian approximation is used, where Luminance is a function of temperature. Many lamps are rated for their 'color temperature' - with daytime (solar) ~5800K, tungsten ~2500K, blue-white > 6000K, etc. These numbers are what lighting designers worry about. ALL measures have explicit or implicit WAVELENGTH dependence, but often the visible light response of the human eye is assumed.
CANDELA (cd): 1/683 Watt per ster-radian (sr) at 5.4E14 Hz (~visible light). The ster-radian is the angular area (or solid-angle) defined by a spherical segment one radian (57.3 degrees) on a side, centered on the light source. The entire sphere around a source has 4 pi ster-radians of solid angle extent.
LUMENS = flux from 1 cd per sr. Modern lightbulbs including CFLs often have Lumen ratings printed on their packaging, e.g. 2000 Lumens @ 4500K.
LUX = luminous emittence (lumens/sq-meters), but can also be used for illumination (see below & Table 2, wiki link below).
NITS: candelas per meter-squared. A laptop LCD screen might produce 300 nits. Theatrical tradition is to use the "foot-Lambert" = 3.4 cd/meter-squared.
Magnitudes, used astronomically, are similar, with m_V = 0 equal to 2.54E-6 lux at the top of our atmosphere (no extinction).
Similarly, Intensity, Flux, Emissivity and/or Radiance refers to quantifying the source output. Intensity can be expressed in cgs units as erg/cm2/s/Hz/sr, and in MKS/SI units -- http://en.wikipedia.org/wiki/Light#Units_and_measures . http://old.nightwise.org/sqm.htm
ILLUMINATION refers to the light measured at a surface some distance from the source of light. These numbers are what quantify glare and light-trespass in the case of badly designed lighting.
FOOT-CANDLES: lumens/sq-foot, somewhat archaic but still common in many municipal codes addressing lighting. Full moon light delivers 0.01 fc on the ground. Denver streetlights deliver 2 or so fc on adjacent turf. Overlit outdoor facilities exceed 20plus fc on adjacent areas.
LUX = measures light incident on a surface, the illumination per meter-squared per lumen, proportional to Watts per meter-squared per ster-radian.
Many additional units exist: Stilbs, Rayleighs, Lamberts, m_10, Blondels, Skots,Brils, and others. Ultimately these should all be related to fundamental physics units like Joules and Watts, etc. For starters, see: http://en.wikipedia.org/wiki/Light#Units_and_measures , http://en.wikipedia.org/wiki/Stilb_(unit) , http://en.wikipedia.org/wiki/Rayleigh_(unit) , http://en.wikipedia.org/wiki/Lambert_(unit) , http://old.nightwise.org/sqm.htm .