Quality of lighting is important.
T5-HO (T5 Lighting) fixtures have an elevated CRI of 85, which is better than all of the HID designs currently found on the market, except for the newest ceramic pulse-start metal halide lamps. IESNA reports that fluorescent luminaries with a CRI of 85 provide similar brightness impressions using 25% less lumens than lamps with a CRI of 60.
It is generally accepted that lamps with a high scotopic to photopic ratio (lamps from the blue-end of the color spectrum are typically those designated with a higher color temperature) provide better visual acuity. Another important consideration is that a well-designed fluorescent high bay fixture will reduce glare, improve contrast ratios, and increase vertical foot-candles.
Typically, two issues will occur with HID lighting systems. First, more fixtures are required to compensate for the lumen depreciation, which raises the initial foot-candles, energy output and the installation cost. Or, the system depreciates down to an undesirable lighting level that requires a re-lamping cycle sooner than expected, therefore increasing the cost of ownership through maintenance.
“Does it cost more to maintain a fixture with multiple lamps than a fixture with one lamp?”
Metal halide lamps depreciate rapidly and tend to shift in color. For this reason we see metal halide lamps replaced at 14,000 to 16,000 hours of operation. This might happen during the third year of ownership. A fluorescent lamp will continue to provide light output right up to end of life at around 20,000 hours with no more than 10% lumen depreciation.
Because fluorescents lamps provide instant re-strike, they are often combined with controls to switch off when not needed. This not only saves energy, but also extends the calendar life of the lamp. The re-lamp scheduled for the fourth year of operation is now extended out to the fifth. If a single lamp fails in a metal halide fixture, the space is dark. With multiple lamps in a fluorescent fixture, you will probably not notice the single lamp that has failed or at least be put in to a critical maintenance mode.
What are you willing to accept?
Is it cost-efficient to waste energy on fixtures that are only putting out 50-60% of their potential? What about having to perform group re-lamping to maintain maximum light output? Isn’t it a wiser investment to give up a few lumens initially in order to have a more consistent lumen output over the course of a lamp’s life? Wouldn’t switching the lamps off when they’re not needed extend the period between re-lamping cycles? Wouldn’t the combined energy and maintenance savings of a fluorescent lighting system contribute to a company’s bottom line?