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Section Descriptions

Hi-Bays and Lo-Bays:
HID or Fluorescent?

In most hi- and lo-bay applications, fluorescent offers a wealth of advantages simply not possible with metal halide—and almost always at a lower operating cost.

Fluorescent Advantages

•	Energy Efficiency – The higher lumens* per watt of fluorescent systems translates into big energy savings. Maintained footcandles are almost always better per energy dollars spent.
•	Excellent Lumen Maintenance – T5 and T8 fluorescent lamps lose only 5-6% of their lumen output between the rated initial and maintained lumens (maintained lumens are calculated at 40% of rated life). By contrast, standard metal halide lamp lumens typically deteriorate about 35% over the same period. As the lamps continue to age, the difference becomes even more pronounced.
•	Instant Restrike – In the event of a power interruption, fluorescent lamps are back on instantly, unlike HID sources which can take several minutes to restrike.
•	Control Friendly – The instant-on capability of fluorescent lamps makes them ideal for use with occupancy sensors and photo cells, further increasing energy savings. Plus they are more cost-effective and versatile when it comes to dimming.
•	Improved Color Rendering – T5 lamps have a Color Rendering Index of 82 and T8 lamps are typically 75 or 82. Metal halide lamps, on the other hand, have a CRI of 70 (coated) or 65 (clear), which negatively impacts visual acuity. New studies are showing that photopic lumens (raw, measurable light) may be less important to our ability to make visual distinctions than scotopic lumens (which take into account the eye's ability to perceive more accurately when colors are well rendered).
•	Linear Source – In warehouses, loaded fork lifts can cast shadows on storage racks, making tasks difficult or even dangerous. In retail, HID point sources can create unwanted shadows. Linear fluorescent lamps provide light from many angles, reducing troublesome shadows.
•	Negligible Color Shift – Unlike metal halide, fluorescent lamps maintain consistent color throughout their life.
•	Color Choices – Fluorescent sources offer a wide range of color options.
•	Improved Lamp Life – Fluorescent lamps last two to three times longer than metal halide lamps of 250W or less, based on lamp manufacturers' published data.

Metal Halide Advantages

•	Wide Temperature Range – Metal halide lamps operate reliably in unconditioned spaces where temperatures can exceed 120°F or fall below 50°F. Light output from fluorescent lamps can drop off in extreme temperatures.
•	Lower Installed Cost – Basic metal halide hi-bay systems are typically less expensive to install (although higher operating costs usually erase any savings in a matter of months).
•	Massive Lumen Packages – Extreme mounting heights may lend themselves better to 1000W metal halide.
•	Severe Environments – A variety of HID hi-bays are designed expressly for applications that are corrosive or exceptionally dirty, are subject to vibration or violent impact, or require hazardous location ratings.

*Lumens are a measurement of the total light emitted by a lamp.

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