Somebody points at a 400 watt metal halide and asks what LED replaces it. The honest answer is that wattage is the wrong unit for the question, but there is a defensible table, and there is a reason the old rules of thumb now overshoot.
Why wattage comparisons mislead
Watts measure what a fixture consumes. Lumens measure what it produces. A metal halide lamp and an LED fixture turn watts into lumens at completely different rates, so any equivalence between them is really a lumen comparison wearing a wattage costume.
Two things make the gap wider than most people expect.
Initial lumens versus mean lumens
A metal halide lamp is at its brightest in the first hundred hours and falls from there. By the time it is halfway through its rated life it is typically producing somewhere around 60 to 70 percent of its initial output, and plenty of the fixtures you are quoting against are well past that. The number on the lamp box is initial. The light in the building is mean, or worse.
A quality LED fixture with an L70 rating holds 70 percent of initial output at the end of its rated life, which is usually 50,000 hours or more. Over the practical life of the installation the LED is far closer to its nameplate than the lamp it replaced.
Where the light goes
A metal halide lamp radiates in every direction, and the fixture then tries to collect that light and aim it down with a reflector. A meaningful share never makes it out. An LED fixture emits down to begin with, so more of what it produces lands where you want it.
Put those together and a fixture that produces fewer lumens on paper can deliver more usable light on the floor.
The equivalence table
These are working starting points for a one for one replacement at similar mounting heights, assuming a modern fixture in the 130 to 150 lumens per watt range.
| Existing | LED replacement | Typical LED output |
|---|---|---|
| 175W metal halide | 40 to 60W | 6,000 to 8,000 lm |
| 250W metal halide | 60 to 100W | 8,000 to 14,000 lm |
| 400W metal halide | 100 to 150W | 14,000 to 21,000 lm |
| 750W metal halide | 200 to 240W | 28,000 to 34,000 lm |
| 1000W metal halide | 240 to 320W | 34,000 to 45,000 lm |
| 150W high pressure sodium | 40 to 50W | 5,500 to 7,000 lm |
| 250W high pressure sodium | 70 to 100W | 10,000 to 14,000 lm |
| 400W high pressure sodium | 120 to 150W | 17,000 to 21,000 lm |
Note the ranges. The old shorthand was to divide metal halide wattage by three, which lands a 400 watt fixture at 133 watts. That was reasonable when LED efficacy sat around 100 lumens per watt. At 140 lumens per watt, the bottom of the range is often enough, and on a building where the existing lamps are old and dim, the bottom of the range can still be an improvement people notice.
Do not use the table when the mounting height or the task changed. If you are also adding racking, raising the ceiling, or the space is being repurposed, size it from foot candles instead. That method is in how many high bays do you need.
Check it with the lumen math
If you can find the original lamp's rated initial lumens, the check is quick.
Mean output at end of life ≈ 36,000 × 0.65 = 23,400 lm
Fixture efficiency ≈ 70% = 16,400 lm delivered
LED needed to match delivered: ~16,000 lm
At 140 lm/W that is 115 watts
Which lands inside the 100 to 150 watt band in the table, and explains why the low end of the band is usually the honest number rather than the safe one.
Two things that generate complaints
The color shift
High pressure sodium is deeply orange, somewhere near 2000K. Metal halide drifts badly with age, often toward green or pink, and no two lamps in a building drift the same way. Put 5000K LED in and the space looks completely different. That is usually the point, but if nobody warned the owner, the first reaction can be that it looks cold or clinical rather than that it looks correct.
Say it up front, and where the space is customer facing, consider 4000K instead of 5000K. It reads clean without reading blue. Most of what we stock is field selectable, so you can set one fixture, look at it, and then set the rest.
Glare
Metal halide in an old reflector is diffuse and somewhat forgiving. A bare LED array is a small, very bright source. At low mounting heights, or anywhere people look up, that reads as glare even when the foot candle level is correct. Look for a diffused lens or a higher fixture rather than more output.
The economics
Metal halide retrofits carry the best payback in commercial lighting, for three reasons that stack.
- The energy delta is large. 400 watts down to 120 is a 70 percent cut, and these fixtures usually run long hours.
- The maintenance stops. Metal halide lamps need replacing every few years, and in a high bay that means a lift, two people and a shutdown. That labor line often exceeds the energy saving.
- The rebate is at its highest. Utilities pay well on metal halide and high pressure sodium replacement because the verified savings are so large. Details in how utility rebates work.
The fixture also has to be on the DesignLights Consortium list on the day it goes in, or the rebate does not pay regardless of how good the savings look.
Where each replacement lives
| Old fixture | Usually replaced by |
|---|---|
| Warehouse or shop high bay | UFO or linear high bay |
| Parking lot shoebox on a pole | LED area light |
| Building mounted flood or wall light | Wall pack or flood light |
| Gas station or garage canopy | Canopy fixture |
| Low bay in a shop or garage | Strip light or low wattage high bay |
Send us the existing fixture count
Tell us what is up there now, the mounting height and the hours it runs. We will come back with the LED replacement, the energy saving and what the utility pays for the swap.
Get a retrofit quote