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Energy Savings Through Improved Lighting Design and Engineering
Tommy Govén
AB Fagerhult, Åsögatan 115, 116 24 Stockholm, Sweden
Abstract
New purpose-designed luminaires for theT5 fluorescent tube provide the opportunity to use energy more efficiently and in a more environmentally friendly way in lighting applications. A mirror-louvre fixture optimised for the new T5 tube using improved reflector material can show an improvement in efficiency of about 35% over an equivalent T8 mirror louvre fixture with a high-frequency (HF) ballast and a standard aluminium reflector. The corresponding improvement in efficiency shown over a luminaire of the same type with a conventional ballast is about 65%. Of this overall improvement in efficiency, 25% can be attributed to the increased luminaire output ratio (LOR). The lamp system contributes a maximum of 7% (for a HF ballast) or 30% (for conventional ballast).
The improvement in efficiency of up to 35% compared to a T8- mirror-louvre fitting with HF can be broken down as follows:
? Higher nominal luminous flux of T5-lamp (89?95lm/W*) ª7%
?Improved aluminium reflectors and louvres (ª86?95%) ª10%
?Higher lamp luminous efficacy at 35°C (ftop 25?35°C) ª10%
?Improved efficacy due to smaller lamp diameterª5%
?Energy saving (1,07 x 1,10 x 1,10 x 1,05)ª35%
*) Taking nominal luminous flux for T5-28/35W and HF-ballast with an electrode heating cut-off.
A lower improvement in efficiency will be obtained for T5-luminaires without mirror louvre. T5 luminaire which is equipped with an improved specular aluminium reflector without a louvre will only show an improvement in efficiency of about 10% over an equivalent T8 luminaire with an HF ballast.
In this case the figure increases to about 35% if the T8-luminaire is equipped with conventional ballast.
Of this overall improvement in efficiency, about 5% can be attributed to the increased luminaire output ratio (LOR) due to a lower ambient temperature within the luminaire and less reflected light.
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