By Chris Choi, Technical Sales Manager at MVS Lighting
Replacing high-pressure sodium (HPS) street lights with LED is one of the most common retrofit projects we support, and also one of the easiest to get subtly wrong. A straight watt-to-watt swap based on a generic conversion table can leave a road under-lit or non-uniform, even when the new fixture is technically “brighter” on paper. Converting correctly means treating it as a lighting redesign around the existing poles, not a one-for-one lamp replacement.
Why You Can’t Just Match Old Wattage to New Wattage
HPS and LED don’t produce or distribute light the same way. HPS lamps radiate in most directions at once and lose a meaningful share of their output to spill, glare, and light that never reaches the road. LED fixtures are directional by design, so a much larger share of their rated output actually lands where it’s supposed to. This is the core reason a lower-wattage LED fixture can outperform a higher-wattage HPS lamp on the same pole — it isn’t a marketing claim, it’s a difference in how efficiently the light gets used.
As a general starting reference, a 150W LED fixture is commonly used to replace 250–400W HPS lamps, depending on the specific HPS lamp’s actual output and the road’s lighting requirements. That range is wide because HPS lamps vary in efficacy and the replacement also depends on pole height, spacing, and the target lux or luminance for the road — it isn’t a fixed 1:1 substitution across every project.
What Changes Beyond the Lamp Itself
Distribution pattern. HPS fixtures typically use a broader, less controlled light spread. Swapping in an LED fixture with a mismatched distribution type can leave gaps in coverage even if the new fixture is objectively more efficient — the distribution type needs to be selected for the existing pole spacing, not assumed to carry over from the old fixture. See our distribution types guide for how to match distribution to your existing layout.
Color temperature. HPS produces a warm, yellow-orange light around 2000K. LED conversions typically move to a cooler white, and getting the color temperature right matters for both visibility and resident acceptance — jumping too high in an effort to look “modern” is a common misstep. See our color temperature guide for the range we’d recommend.
Lux and luminance targets. A conversion project is a good opportunity to actually verify the road against its applicable lux, luminance, and uniformity targets — rather than assuming the original HPS installation was correctly designed in the first place. See our lux and luminance levels guide for the background on these metrics.
Retrofit vs. Full Pole Replacement
Most conversion projects retrofit the existing poles rather than replacing them, which keeps costs down but adds a constraint: the new fixture and its distribution need to work with pole height and spacing that are already fixed in the ground, not designed from scratch. This makes the conversion calculation somewhat different from a new-build project — instead of solving for the ideal pole height and spacing together, you’re solving for the best fixture and distribution given spacing that can’t change. For the underlying design logic this draws on, see our road lighting design guide.
Full pole replacement becomes worth considering when the existing poles are structurally unsuitable for the new fixture’s weight and wind loading, or when the project also wants to change pole height or spacing as part of the upgrade — at that point it’s closer to a new-build design than a retrofit.
Don’t Skip the Simulation Step
The biggest mistake we see in conversion projects is treating the wattage table as the whole answer and skipping verification. A wattage that “should” work based on a general conversion guideline can still under- or over-perform once it’s checked against the actual pole spacing, distribution type, and road width already in place. Running the proposed fixture’s IES file through a lighting simulation against the existing layout confirms the conversion will actually hit its lux, luminance, and uniformity targets before the poles go up — not after. See our street light maintenance and lifespan guide for what to expect from the new fixture once it’s installed.
Additional Benefits Worth Factoring Into the Business Case
Beyond the lighting performance itself, HPS-to-LED conversions typically bring a meaningfully longer rated lifespan than HPS lamps, which reduces relamping frequency and maintenance visits. They also open the door to dimming and smart control strategies that HPS fixtures generally can’t support, which can add further energy savings on top of the base efficiency gain from the light source switch itself. For a full look at the cost side of this decision, see our street light pricing guide.
Common HPS-to-LED Conversion Mistakes
Matching wattage without checking distribution. The same wattage can perform very differently on the road surface depending on how the light is distributed — a straight wattage match doesn’t guarantee equivalent coverage.
Assuming the original HPS layout was correctly designed. Older installations weren’t always designed to current uniformity standards; a conversion project is a reasonable point to actually verify this rather than carry the assumption forward.
Skipping simulation because “the wattage table said so.” Reference ranges like the one in this article are a starting point, not a substitute for checking the specific pole spacing and road width involved.
Ignoring color temperature acceptance. Jumping to an aggressively cool color temperature during a conversion is a common source of resident complaints that a slightly more conservative CCT choice would have avoided.
In my view, the value of converting HPS to LED comes down to three things: efficiency (HPS typically delivers roughly 80–100 lm/W and needs several minutes to warm up, while LED commonly reaches 120–150 lm/W and switches on instantly), fewer maintenance visits thanks to a longer rated lifespan, and much better color recognition at night (HPS CRI is typically around 20–30, versus 70+ for LED). Actual savings and service life still depend on project conditions and fixture quality, and LED should not be considered completely maintenance-free.
FAQ
What LED wattage replaces a 250W HPS street light? As a general starting reference, 150W LED fixtures are commonly used to replace 250–400W HPS lamps, though the right figure for a specific project depends on the LED fixture’s actual efficacy, the existing pole spacing, and the road’s lighting target — always verify with a simulation before finalizing.
Do I need to replace the poles when converting from HPS to LED? Not usually. Most conversions retrofit the existing poles with a new fixture, as long as the pole can structurally support the new fixture’s weight and wind load. Full pole replacement is typically only needed if the existing poles are unsuitable or the project also wants to change height or spacing.
Will LED street lights look too bright or too blue after converting from HPS? Not if the color temperature is chosen carefully. HPS produces a warm amber tone, and jumping to a very high LED color temperature can feel like a stark change; a more moderate CCT choice generally gets better acceptance from residents while still meeting visibility requirements.