Metal-halide systems are often good candidates for LED upgrades because LED can reduce connected load, improve controllability, eliminate warm-up/restrike behavior, and reduce lamp-and-ballast maintenance. The correct replacement, however, cannot be determined from the metal-halide lamp wattage alone.
Why a wattage conversion table is only a rough starting point
Two fixtures using the same metal-halide lamp can deliver very different useful light because reflector design, lens condition, orientation, mounting height, ballast losses, lamp age, and distribution all affect the result. Likewise, two LED fixtures with the same input wattage can have different output and optics.
Use wattage to understand energy consumption. Use manufacturer photometric and product data to determine lighting performance.
Document these five inputs before choosing the LED family
Retrofit kit or complete fixture replacement?
Retrofit the existing housing when
- The housing, mounting, lens, and mechanical condition are worth preserving.
- A listed retrofit solution is available for the application and installation method.
- Labor, disposal, architectural appearance, or access makes full replacement less attractive.
- The resulting optics and thermal conditions still satisfy the project.
Replace the complete fixture when
- The existing housing, reflector, lens, wiring, or mounting condition is poor.
- The project needs a different distribution, mounting method, controls package, environmental rating, or visual form factor.
- A complete LED luminaire gives a cleaner path to the required photometric performance or documentation.
How to compare candidate LED replacements
- Compare delivered lumen output and distribution using the manufacturer’s current data.
- Check mounting height, fixture spacing, and the actual lighting task; use a photometric layout when the project depends on uniformity or minimum light levels.
- Verify voltage, controls, surge protection, environmental rating, mounting, dimensions, and accessories.
- Check the exact configuration’s listings, warranty, and project-required documentation.
- If an incentive program matters, verify the exact product against the current program rules before purchase or installation.
Calculate energy savings separately from equivalence
Once a technically suitable LED option has been selected, compare the existing system input watts—including ballast losses where known—with the LED input watts and operating schedule. That gives an energy-use comparison without using energy savings as proof that the fixture is optically or mechanically equivalent.
Example method: annual kWh = fixture quantity × input kW × annual operating hours. Apply the customer’s actual utility rate and control schedule rather than a generic national assumption.
The practical takeaway
Start with the old wattage if that is all you have—but do not stop there. The safest LED conversion is the one that preserves or intentionally changes the project’s lighting performance while also fitting the electrical, mechanical, environmental, controls, and approval requirements.