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NIGHTSKY® Optical Systems
Star-Shield® & Opti-Shield®
State-of-the-Art Optical Systems
Addressing Dark Sky Concerns
Sternberg Lighting's commitment to quality extends to superior photometric performance. Our NIGHTSKY® optical systems address both Dark Skies and Light Pollution issues that concern our customers and our industry. Our continuous reflector engineering efforts, have enabled us to become the leader in reflector design and photometric performance. These optical systems are available in a majority of our ornamental products increasing the specifier's options on roadway and area lighting applications.
Industry standards on luminaire efficiency once were measured on the amount of light a luminaire can throw down and the distance in which they can be spread apart. Today, the requirement has become much more sophisticated. Now we address the quality of light, Light Pollution, Cut-off and veiling luminance or glare. Our optical systems address all these issues, and are available in a number of light distributions.
Photometry Terms & Lighting Terminology
- Cut-Off Lighting:
- There are four classifications of cut-off that describe the optical performance of a luminaire:
- Full Cut-Off: A luminaire is considered full cut-off when no light is present at or above a horizontal plane.
- Cut-Off: A luminaire is considered cut-off when a minimum amount of light is directed at a horizontal plane. Light above the horizontal plane is limited to less than 2.5% of the total lamp lumens.
- Semi Cut-Off: A luminaire is considered semi cut-off when more light is permitted at a horizontal plane than in the cut-off luminaire. Similar to cut-off, light above the horizontal plane is limited to less than 5% of the total lamps lumens. The amount of light emitted above the luminaire is negligible.
- Non Cut-Off: Non cut-off luminaires produce considerable light above the horizontal plane.
- Efficiency:
- A ratio of light emitted from a luminaire to the light produced by the light source.
- Glare:
- Glare occurs when a bright light source causes the eye to continually be drawn toward the bright image. The brightness of the source prevents the viewer from adequately viewing the intended target. Glare may create a loss of contrast or an after-image on the retina of the eye, reducing overall visibility. Two classifications of glare are discomfort glare and disability glare. Discomfort glare does not necessarily keep the viewer from seeing an object but does cause physical discomfort. Disability glare occurs when the bright source is close to the axis of view, causing stray light to scatter in the eye. This obscures the primary image on the retina and may prevent the viewer from seeing.
- Illuminance (E avg):
- The measurement of light striking a surface or plane at a point. It is expressed either in lumens per square foot) footcandles, the English unit) or lumens per square meter (lux, the metric unit). 1 footcandle = 10.76 lux.
- Light Trespass (Spill Light):
- Light trespass is unwanted light directed onto adjacent properties. Light trespass has become an increasing concern as residences and commercial developments are constructed closer to each other. Light trespass may be perceived as more obtrusive during the dark versus at dusk.
- Luminance (Brightness - L avg):
- A term that measures directional brightness of a light source, or of a surface that is illuminated and reflects light. It is expressed as candelas/meters squared (metric units) or Footlamberts (English units).
- Artificial Sky Glow (Light Pollution):
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Sky glow is a “glow” of light that surrounds highly populated areas and reduces the ability to view the night-time sky. Sky glow is of particular concern in areas where the observatory industry is most prevalant. Light emitted or reflected into the sky washes out the contrast of the stars against the dark sky, making it difficult to view stars and other heavenly bodies. Sky glow results from light illuminating the sky in two ways:
1. Directly: from luminaires producing light above the horizontal plane.
2. Indirectly: from light produced from a luminaire below the horizontal, but reflected upward from surrounding surfaces.