The Clear Lamp Advantage: Stingray Energy Systems LLC

Point-Source Lighting and the Clear Lamp Advantage

Point Source Lighting

Everyone has experienced the invigorating crispness of a clear, sunny day and the captivating twinkle of the nighttime stars. However, many are surprised to learn that the qualities we associate with these visual experiences are largely a consequence of the size and number of light sources involved. There are at least three contributing factors.

The first relates to viewing the light source, either directly or via specular reflection (from a glossy surface). Large numbers of small, highly luminous light sources result in a scene that is captivating, invigorating, clear and relatively comfortable. As the light sources become larger, the propensity for glare increases exponentially, even when the relative brightness is reduced to maintain equivalent lumen output. This condition persists until the light source becomes so large that it constitutes a significant portion of the field of view, at which point the visual system adapts to the source brightness and glare is reduced.

A second key characteristic of point-source lighting is that shadows are especially well defined. This is because the occlusion of small light sources takes place over a smaller angular dimension. That is, with relatively little change in viewing position, a light source goes from being fully visible to fully occluded as a consequence of an opaque intervening object. This means that the shadows cast will have sharply defined boundaries resulting in a scene characterized by high contrast and enhanced visual clarity.

The third characteristic relates to the directional strength of the light field. Light radiates outwardly from a single point-source. It travels only in a straight line and can therefore only illuminate one side of an object in its path. Consider the appearance of the moon during a quarter phase. As multiple light sources are added, or the size of the light source increases, this characteristic becomes softened and a complex light field is produced. The directionality of light within a scene dictates the way that three-dimensional objects will appear. It determines which aspects of the object will be in highlight as well as the strength of modeling, and therefore has a significant impact on the overall appearance of a scene and the quality of the visual data that can be extracted from it. These are well-established concepts that have been exploited in stage and display lighting for centuries.

The term “Point-Source Lighting” refers to both point-like sources of light (lamps) as well as the compact luminaires that utilize them. Point-source lamps support the design of luminaires that are similarly compact. When properly designed, these luminaires can provide efficient, glare-free light that produces a bright, high-clarity visual environment characterized by impressions of cleanliness, vibrancy and enhanced three-dimensionality. By contrast, the use of extended light sources often leads to fixtures with less than elegant size and proportion that can visually clutter a space and attract undesired attention due to their size and lack of adequate lamp shielding. Shadows are relatively softer, the strength of three-dimensional modeling is reduced, and both direct and reflected views of the light source(s) are more glare-prone and ubiquitous.

Decades ago, with the advent of the metal halide lamp, the visual appeal of point-source lighting was complimented by the utility of high efficacy (lumens/watt), high lumen output and long life. High efficacy resulted in energy savings and high lumen output translated to fewer lamps, luminaires and mounting points, which, along with long life, provided installation and maintenance savings. All of these benefits are hallmarks of point-source lighting. Over the past decade, engineering advances have brought about a new generation of Metal Halide lamps: Pulse Start Metal Halide (PSMH) and Ceramic Metal Halide (CMH). These Advanced Metal Halide technologies are now taking point-source lighting to unprecedented levels of performance (see Industrial Lighting with Advanced Metal Halide below for more details).

The Clear Lamp Advantage

From the standpoint of optical design, point-source lamps are considered the theoretical ideal. When light radiates from a singular location in space, the geometry of the optical system can be designed to precisely and efficiently redirect that light to achieve nearly any desired distribution of light. Through the application of advanced optical techniques, point-source lamps also provide the unique flexibility to tailor beam shape via relative lamp adjustment for the task at hand.

However, the use of point-source lamps (with a clear quartz envelope) can often prove problematic in practice. A clear Metal Halide lamp used in conjunction with precision optics commonly produces unsightly striations, rings and hotspots as evidenced by most adjustable-style flashlights. The issue lies primarily in the fact that common lamps are relatively imprecise devices. The exact position and configuration of luminous elements of the lamp varies from one lamp to the next, and from manufacturer to manufacturer. Thus, it is difficult to develop a highly precise optical system that is simultaneously forgiving in terms of lamp position. These problems become particularly evident when attempting to adjust the focus of the beam through lamp position adjustment, relative to the reflector.

This host of problems is why phosphor-coated lamps are often applied or recommended even though they are less efficacious, reduce optical control, diminish visual sparkle, and are less readily shielded from direct view. Phosphor coatings also produce a relatively unpopular color shift toward the warmer end of the spectrum. These effects are also responsible for the ubiquitous use of brushed metal and white painted reflector finishes. While helping to achieve smooth and consistent light distribution, these design compromises degrade the efficiency and effectiveness of light delivery. The resultant loss of optical control also tends to spread light in a way that compromises flexibility, or the extent to which an adjustable optical system may be "tuned" to a variety of applications.

Stingray’s most advanced optical systems harnesses all the positive aspects of both precision optics and clear point-source lamps while eliminating the negative effects usually associated with combining the two. These systems deliver light in a way that is highly efficient and precise, yet simultaneously smooth and versatile. The net result is that Stingray's optical systems deliver more light, of higher quality and this translates to significantly reduced energy consumption.

Ripples on the surface of water sparkle under point-source lighting. The effect is a result of the sun being imaged on the surface of the water via specular, or mirror-like reflection. Glossy objects exhibit this quality when illuminated by point source lighting.

Lighting quality differences between linear and point-source methods is highly apparent in the above photos. Note differences in the crispness of shadows and strength of modeling.

The above images graphically depict the impact of light source size on optical control. Smaller light sources provide a greater degree of optical control which allows more effective light delivery and better glare management, in addition to flexibility.