400W metal halide lamps are rated at 36,000 lumens! How can fluorescent compare?

What some people don't want you to know is that standard metal halide lamps start with high initial lumens, but light output drops precipitously as lamps age. A quick glance at a lamp catalog shows that maintained lumens (light output at 40% of a lamp's rated life) typically decrease by over one third. After 8,000 hours, that 400W lamp now is 24,000 lumens or lower. And it doesn't stop there. By end of life, lumens drop to 15,000 lumens or less—about 40% of initial. In contrast, six T5 lamps start life at a combined 26,400 lumens (6 x 4,400), decline to 24,800 mean lumens, and stay above 23,500 throughout their rated life. This graph compares three common lamps.

T5 HO lamps run best at 35°C (95°F). Can I use them at room temperatures?

T5 lamps are optimized to operate at ambient temperatures of 35°C (95°F). It is essential to remember that this is the ambient temperature surrounding the lamp, not necessarily the room temperature. Lamp manufacturers have intentionally designed T5 lamps to run better in warm ambients because the heat they generate warms the air around them. More importantly, IESNA* procedures stipulate that photometric tests must be run in a 25°C (77°F) ambient, meaning that the reported performance of any fixture should closely match its actual performance at room temperature.
*Illuminating Engineering Society of North America

I thought T5 HO lamps were rated at 5,000 lumens. Why does Columbia use 4,400?

T5 lumen output is rated over a range of ambient temperatures. At 35°C (95°F), a 54-Watt T5 HO emits 5,000 lumens. Depending on the manufacturer, these same lamps produce 4,400 to 4,500 lumens at 25°C (77°F). Since Columbia Lighting photometric tests are conducted at 25°C, we use 4,400 lumens as a safe, conservative value. This ensures that results predicted by our tests will be as accurate as testing procedures allow.

Can fluorescent sources work at high mounting heights? Do they have enough "punch?"

"Punch" is a term to describe candela delivered to the floor, and again, lumen maintenance plays a key role. As seen in the candela plots below, metal halide delivers lots of light initially, but at 40% of rated life, the advantage is lost and continues to decline.