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How does a lighting professional or facilities manager make an educated choice among a T8, T5 or T5HO linear fluorescent?

Peter Ngai, PE, FIES, LC and vice president of engineering for Peerless Lighting in Berkeley, California, has assessed all three using objective criteria, including:

Wattage,
Efficacy (lumens/watt),
Optimal ambient operating temperature, and
Warm-up time.
Among his findings, which were presented at LightFair International 2003:

When a T8 lamp is operated with reference high frequency electronic ballast with filament cut out, only 28 watts are needed to produce 2,900 lumens. "Therefore, the efficacy of T8 and T5 are the same, and about 10% higher than T5HO," he concludes.
For luminaires with the same physical size, T5 performs better optically than T8.
To match a one-lamp T5HO optical performance, a two-lamp system may have to intensely control the optics. This will most likely reduce the efficiency of the luminaire further.
Addressing the controversy about how different operating temperatures affect photometric reports for T5 and T5HO luminaires, Ngai recommended a testing procedure that references bare-lamp light output to the temperature that the lamp(s) actually operates at inside the luminaire.
Generally speaking, for indirect lighting applications, T5HO is the most desirable light source due to its small size and high lumen package, which enable luminaire designer to create superior optical distributions with minimal loss in efficiency.
Peerless Lighting was the first company to introduce the T5HO lamp technology from Europe in 1996, Ngai says.

"At that time, of course everybody was using T8 lamps. Peerless Lighting was also first to introduce the T8 in the early 1980s, when everyone else was using the T12 lamp," explains Ngai, a leader in the field since joining the company in 1976.

Since then, he has made contributions to the fundamental understanding of lighting theories, optical designs for luminaires and lighting applications. He also collaborates and manages projects in lighting research and education with various institutes, including the University of California at Berkeley, Cornell University and Rensselaer Polytechnic Institute.

Ngai also works with lighting specifiers in lighting designs for their projects, including installations for Cigna, Procter & Gamble, Steelcase, Hewlett-Packard, General Motors, National Archives and Lucent Technologies.