Updated for 2011, this guide covers how to estimate, warranties and quantity discounts, an estimate form, design and engineering fees, service and installation hourly rates, a letter footage chart, and ...
End-system efficiency determines theoretical and practical limits.
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Solid-state lighting (SSL), with light-emitting diodes (LEDs) as the light source, is a growing and essential field, particularly in regard to the heightened need for global energy efficiency. And, in recent years, SSL has experienced remarkable advances in efficiency, light output and quality. Its flexible structure allows scaling, and color combination capabilities, for architectural and decorative lighting applications on both residential and commercial buildings – indoor and outdoor. Further, it has gained acceptance in such diverse applications as illumination, signage and displays.
SSL capabilities are unique and promising, but the industry yet evolves, because technologies, and deeper understanding, continue to unfurl. The available light (i.e. luminous flux, measured in lumens) from a typical LED luminaire, when driven by equivalent electrical power, remains, on average, lower than a commercial, fluorescent light.
The signage industry makes similar claims for neon.
Luminous efficacy, measured in lumens per watt, has escalated for LEDs, says Osram, Cree, and Nichia’s R&D laboratories, but the present figures are substantially lower than their theoretical, achievable limit. I shall attempt to estimate that limit in this column.
Luminous efficacy is a conventional measure of an electrical lighting element’s effectiveness. It’s a measurement of luminous flux per unit of electrical input power and, therefore, measured in lumen/watt (lm/W). Contrastingly, luminous efficiency is specified in percentages where both power units must be either in lumens or watts, depending on what efficiency one is interested in determining. If both are in watts, the result is a complete (or absolute) electrical energy percentage, converted to optical energy, at one instant of time.
This is useful in a world concerned with energy efficiency. However, to determine the visible light (in lumens) for an amount of electrical driving power, we must know the number of lumens being generated per unit of electrical power; this is where efficacy is appropriate.
Because a fixture may hinder lamp output, one must ascertain the luminaire’s efficiency before determining the amount of available light. This efficiency is defined by a ratio of two powers, in lumens; both LED luminaire efficiency and efficacy are directly related to the amount of light the LED produces per unit of electrical power that drives it.
Such concepts apply to all general lighting.
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