How many lumens is a 400W metal halide lamp?

A standard 400W metal halide lamp—probe-start, which is what most warehouses used for decades—puts out about 36,000 initial lumens right when it strikes. Pulse-start versions run a bit hotter, around 39,000 to 40,000 lumens out of the box. But that number is a snapshot, not a promise. Within the first 100 hours, you lose roughly 15% as the lamp stabilizes. By 40% of its rated life (say, 8,000 hours into a 20,000-hour lamp), you're down to 20,000–24,000 lumens. That’s a 35–40% drop before the bulb even fails. And that’s assuming clean reflectors and proper voltage—real shop conditions knock off another 10%.

Compare that to a 150W LED high bay, which delivers a steady 21,000–24,000 lumens for 50,000 hours with no warm-up and almost no degradation. So when someone asks “how many lumens,” the honest answer depends on when you measure. Day one: 36k. Month six: maybe 28k. Year two: closer to 20k. Most people don't replace them because they burn out—they replace them because the light output becomes useless. If you need a consistent 30,000 lumens, a 400W metal halide only gives you that for the first few weeks. After that, it's just a power-hungry heater that happens to glow.