LED fog lights, auxiliary lights and headlight upgrades list lumens, watts, kelvin, a beam type and an IP code. Each measures something different, and a few are easy to misread. Here is what each spec tells you, using listings from our lighting collection such as the 4 Inch LED Fog Lights for Ford F-150 2015-2020 and Super Duty 2017-2022.
Lumens, lux and watts measure different things
A lumen is the unit of luminous flux, the total visible light a source puts out. Lux is the unit of illuminance, the light landing on a surface: one lux is one lumen per square meter. A lux reading depends on distance and on where the beam sends its light, which is why some lighting makers state the distance at which a light still delivers 1 lux. A watt is a unit of power: it tells you how much electrical power the light draws, not how much light reaches the road.
Why raw lumen claims are hard to compare
Many lumen figures are raw lumens: each LED chip's rated output times the number of chips. Effective lumens are measured from the finished light, after losses to heat, optics and assembly. One lighting maker puts typical real-world losses at 10% to 25%, and another's worked example turns 800 raw lumens into 480 effective. A U.S. Department of Energy fact sheet adds that hotter LEDs give less light and lose output faster over their life.
Listings also count differently. Three fog light sets in our collection state their output this way:
| Fog light set | Lumens as listed | Color temperature | Wattage | IP code |
|---|---|---|---|---|
| Ford F-150 2015-2020 and Super Duty 2017-2022, 4 inch | 2,400 lm, per light or pair not stated | 6,000K | 36 W | None listed |
| GMC Sierra 1500, 2500HD, 3500HD 2003-2006, halo DRL | 4,000 lm, per light or pair not stated | 5,500K | 40 W | IP67 |
| Ram 1500 2013-2018 and 1500 Classic 2019-2020 | 4,800 lm per pair | 6,000K | 72 W | None listed |
With one figure per pair, two unstated and none marked raw or measured, the totals cannot be ranked against each other. Wattage works the same way: 72 W against 36 W tells you about power draw, not reach. Compare lights on the same basis, ideally effective lumens for the same number of lamps or lux at a stated distance.
Color temperature in kelvin
Kelvin (K) describes the color of white light, not its brightness. About 3,000K looks warm and yellowish, close to halogen; 4,000K to 5,000K reads as neutral white; 5,000K to 6,000K as a cool, crisp white. The Sierra set lists 5,500K and the F-150 and Ram sets 6,000K, all cool white. The higher number means a slightly cooler tint, not more light.
Beam patterns: spot, flood, combo and fog
- Spot: a narrow, concentrated beam with long reach, suited to high speeds and search work.
- Flood: a wide, short-reach spread for lighting an area while parked or at very low speed, like reverse lights.
- Combo: some reach plus fill around the vehicle; versatile, but suited to lower speeds.
- Driving: concentrated for down-road vision, with more spread than a spot.
- Fog: a very wide, short beam mounted low so light travels under the fog instead of reflecting back at the driver.
Road headlights add a cut-off: a projector low beam gets its sharp top edge from a shield inside the lamp. The 5x7 and 7x6 Inch LED Sealed Beam Headlights list LED projector high and low beams with a sharp Z cut-off line, for vehicles with H6054-type rectangular sealed beams. Off-road patterns are another matter on public roads, as our auxiliary lights guide explains.
IP67 vs IP68
The IP code comes from the international standard IEC 60529 and rates protection against solids and water. The first digit covers dust, and 6 means dust-tight. For the second digit, 7 means the light passed a temporary immersion test in water up to about 3.3 ft (1 m) deep for 30 minutes. An 8 means continuous immersion beyond that, under depth and time conditions the manufacturer sets, so check the stated depth and time.
Immersion ratings do not automatically cover water jets: a light tested against jets also carries a 5 or 6, often as a dual code like IP66/IP67, and road-vehicle codes such as IP69K cover high-pressure and steam cleaning. An IP code describes a lab test, not every trail or car wash. The Trail Sight Lights for Ford Bronco 2021-2026 (Not Bronco Sport) and the Sierra fog lights both list IP67.
FAQ
Is a light with more lumens always brighter on the road?
No. Raw totals can overstate output, and lumens do not show where the light goes. Lux at a stated distance says more about reach.
Is 6,000K brighter than 5,500K?
No. Kelvin describes color, not the amount of light.
What is the difference between IP67 and IP68?
Both are dust-tight. IP67 covers temporary immersion, up to about 3.3 ft (1 m) for 30 minutes in testing; IP68 covers continuous immersion under conditions the manufacturer specifies.
Does higher wattage mean a better light?
Not by itself. Wattage shows power draw; output also depends on the LEDs, the optics and heat.
Compare fog lights and more in our lighting collection, and read our guide to off-road and auxiliary lights for DOT and SAE markings, state rules and aiming. Rules for added lights vary by state, so check yours, and aim any new light after installing.
Brand and model names are trademarks of their respective owners and are used only to identify vehicles. BT Merch Co. is not affiliated with or endorsed by any automaker.
