LEDs Don’t Burn Out. They Fade.

Why LEDs dim instead of dying

An LED doesn’t have a filament to snap. Light comes from electrons crossing a semiconductor junction — they fall into holes in the crystal lattice and release photons. Every hour that junction runs, heat causes tiny structural defects in the crystal. Dopant atoms migrate. New pathways form where electron energy converts to heat instead of light.

The result is a slow, steady fade. A fixture drawing 300 watts on day one still draws 300 watts three years later, but it’s producing fewer lumens. The power that used to become light is now becoming waste heat — which accelerates the very degradation that caused the loss. It’s a feedback loop with no off switch except temperature control.

Industry measures this with the L70 rating: the number of hours until output drops to 70 percent of initial lumens. That 70 percent threshold isn’t arbitrary. It’s roughly where most people notice the difference without a side-by-side comparison. A parking lot that felt well-lit at 100 percent still feels adequate at 85 percent. At 70 percent, you start noticing dark patches where there weren’t any.

Not one of these four fixtures publishes an L70 rating. That’s common in this price range. It doesn’t mean the fixtures are bad — it means you can’t compare their expected fade rates from a number on the box. You have to read what the specs do say and work backward.

Junction temperature is the whole game

Every 10°C rise in junction temperature roughly halves the LED’s expected lifespan. That’s the single most important sentence in outdoor lighting, and it explains why identical-wattage fixtures from different manufacturers can have wildly different fade rates.

The junction temperature depends on three things: how hard the LED is driven (current), how well the fixture moves heat away from the junction (thermal design), and the ambient temperature where you mount it. You control the third one. The manufacturer controls the first two — and almost never tells you what they are.

A well-designed heatsink with high thermal conductivity and enough surface area keeps the junction cool even in August. A fixture with a small, thin housing traps heat against the LEDs. Both will look identical in a product photo. Both will light up identically on the first night. The difference shows up at month eighteen.

This is why wattage alone tells you almost nothing about longevity. A 150-watt fixture with excellent thermal management will hold its lumens longer than a 300-watt fixture with a cheap housing — because the 300-watt fixture is generating twice the heat with potentially no better path to dissipate it.

What lumens per watt actually tells you

Luminous efficacy — lumens divided by watts — is the closest thing you get to a thermal management indicator without cracking open the housing.

Higher efficacy means the LED is converting more electrical energy into light and less into heat. A fixture producing 150 lumens per watt runs cooler at the junction than one producing 100 lumens per watt at the same wattage, because less energy is wasted as thermal load. That lower junction temperature translates directly into slower degradation.

The gap between these fixtures is significant. The AIKVSXER 200W produces 30,000 lumens from 200 watts — 150 lumens per watt. The AIKVSXER 300W claims 75,000 lumens from 300 watts — 250 lumens per watt. If that 250 figure is accurate, it’s an extraordinarily efficient fixture, and the lower thermal waste per lumen should mean slower fade over time.

But efficacy numbers on the box are measured at room temperature with a fresh LED. Real-world efficacy drops as junction temperature rises and as the fixture ages. A fixture that starts at 250 lm/W in a lab might operate closer to 200 lm/W on a hot roof. The initial number still matters — higher is still better, all else equal — but treat it as a ranking tool, not an absolute promise.

Multi-fixture packs and the uneven fade problem

Buy a pack of three or six fixtures, mount them across a property, and they’ll all start at the same brightness. They won’t stay there.

Every mounting location has a different thermal environment. The fixture on a south-facing wall gets direct afternoon sun. The one under an overhang stays cooler. The one next to an HVAC exhaust vent gets a constant stream of hot air. Same fixture, same LED, same driver — different junction temperatures, different degradation rates.

Within two years, you’ll have one fixture that’s noticeably dimmer than the others. Replace just that one with a new unit, and now you have a fixture at 100 percent output next to fixtures at 80 percent. The brightness mismatch is immediately visible. Your choices are to replace them all — expensive — or accept uneven light — ugly and potentially a liability issue if the dim zone covers a walkway or entrance.

This is the real cost calculation with multi-packs. The per-fixture price is lower. The long-term replacement logic is harder. If you’re lighting a space where even illumination matters — a commercial lot, a church parking area, a loading dock — factor in that you’ll eventually be replacing fixtures in sets, not singles, regardless of how they were sold.

Dusk-to-dawn sensors: what wears out besides the LED

A photocell is a simple device — a photoresistor whose resistance changes with ambient light, switching a relay that controls the fixture. Simple doesn’t mean permanent.

The photoresistor itself is a semiconductor, and it’s mounted on the exterior of the fixture, exposed to UV, rain, and the same thermal cycling that stresses the LEDs. Over years, the sensor’s activation threshold can drift. If it drifts toward less sensitivity, the fixture turns on later in the evening and off earlier in the morning — you lose coverage at the margins of darkness. If it drifts toward more sensitivity, the fixture activates during overcast afternoons, adding operating hours and thermal stress you didn’t budget for.

A sensor that fails entirely typically fails to one state: always-on or always-off. Always-on doubles your operating hours and accelerates LED degradation — your 50,000-hour fixture is now running 8,760 hours per year instead of 4,000, hitting L70 in under six years instead of twelve. Always-off is obvious and gets fixed. Always-on might not be noticed for months, especially on a fixture you don’t see during daylight.

Two fixtures in this set — the AIKVSXER 200W and the Juyace three-pack — include dusk-to-dawn operation. The LEDMO includes a photocell on the wall mount. If you’re installing any of them, check the sensor once a season. Walk the property at noon on a sunny day. If a fixture is lit, the sensor has drifted or failed.

Color temperature and perceived brightness aren’t the same number

A 5000K light and a 6500K light at the same lux level don’t look equally bright to your eye. Human vision peaks in sensitivity around 555 nanometers — green-yellow. A 6500K source pushes more energy toward the blue end of the spectrum, but it also contains substantial energy near that peak sensitivity wavelength. The result is that cooler-white light often appears brighter than warm-white light even when a meter reads identical lux.

This matters when you’re mixing fixtures or replacing one in a set. Swap a failed 5000K fixture with a 6500K replacement, and the new one will look conspicuously bluer and brighter — not just because it’s new, but because of the spectral difference. Over a whole property, consistency matters more than absolute output. Pick a color temperature and stick with it.

For parking lots and security lighting, 5000K to 6500K is the normal range. Below 5000K starts to look residential. Above 6500K starts to look clinical. Within that range, the choice is aesthetic, not performance — 6500K isn’t meaningfully better at illuminating pavement than 5000K is.

How to decide what you’re actually buying

Start with total lumens needed, not wattage. Wattage tells you what you’ll pay the utility company. Lumens tell you what you’ll see. A 200W fixture at 150 lm/W and a 150W fixture at an unknown efficacy could produce anything from the same light to vastly different amounts — you can’t tell without the lumen number.

Next, count fixtures and map thermal environments. A six-pack at 300 watts each is 1,800 watts of total heat generation across your property. That’s substantial electrical infrastructure — dedicated circuits, potentially a panel upgrade. But six smaller sources also mean more uniform coverage with less reliance on any single fixture. If one fades faster than the others, the remaining five still cover most of the lot.

Then consider the replacement math. A single high-output fixture is cheaper to replace — one unit, one mounting point, one set of wiring. A six-pack is cheaper per fixture up front but commits you to managing six separate degradation timelines. When the first one noticeably dims, you’re deciding whether to replace one and accept the brightness mismatch, or replace all six and waste the remaining life in the other five.

Finally, check for IP ratings. Outdoor fixtures that lack ingress protection ratings will still work in rain — most LED housings are functionally weather-resistant. But without a tested and rated seal, you’re relying on manufacturing consistency rather than engineering specification. In a dry climate, that’s probably fine. In the Gulf Coast or Pacific Northwest, it’s a gamble that compounds with every year of thermal cycling and gasket aging.