Headlight & Lighting Guides
Most lighting jobs go wrong at the ordering stage, not the wrenching stage — the bulb arrives and the base does not fit, or the assembly arrives and the connector has three pins instead of two. These 16 guides are written to stop that: work out exactly which part you need, understand what it does, choose the right upgrade, then fit and aim it properly.
Every guide is vehicle-agnostic — the reference data (base codes, lamp dimensions, interchange rules, bulb positions) applies to any car, truck or SUV. Nothing here quotes a price; new parts route to Amazon and used or OEM parts route to eBay Motors, where the live listing is the only honest price.
Start here: which guide answers your question?
| If you're asking… | Read this |
|---|---|
| How big is my headlight? (7-inch round, 5x7, 4x6…) | Headlight Size Guide Housing dimensions — and why a modern assembly has a part number instead of a size |
| What bulb number does my car take? | Bulb Size Reference Chart Base-code chart: H11, 9005, 9006, H7, H4, 9012, H13, D-series |
| Is this bulb the same as that one? | Bulb Cross-Reference & Interchange Interchange cheat-sheet — H4 = 9003 = HB2, but 9005 ≠ 9006 |
| Which bulb do I have in there right now? | Bulb Cross-Reference & Interchange Three ways to identify a bulb you can hold in your hand |
| What is the part called that I need to replace? | Parts of a Car Headlight Headlight anatomy plus a symptom → part diagnostic |
| What is that other light on my car for? | Car Light Parts Explained Every exterior and interior lamp position, front to back |
| Will LED bulbs actually work in my housing? | Projector vs. Reflector Headlights Reflector vs projector — the housing decides whether an LED swap works |
| LED or HID? | LED vs HID Headlights Brightness, beam pattern, lifespan, install effort |
| My new LEDs flicker or throw a bulb-out warning | Fix LED Flicker & Error Codes The four-rung fix ladder, matched to your symptom |
| I just swapped bulbs and now I am blinding people | How to Aim Your Headlights The 25-foot wall method, in about ten minutes |
| Are these even legal? | Are LED Headlights Legal? Assembly vs conversion bulb, region by region |
| My lenses are hazy — polish or replace? | Restoration vs. Replacement What restoration actually fixes and when it will not hold |
Fitment & identification — what part do I actually need?
Start here if you know something is out but not what to order. These four cover the two different questions hiding inside "what size headlight do I need": the bulb base code, and the housing itself.
Headlight Size Guide: Bulb Code vs. Housing Dimensions
"What size headlight do I need?" has three different answers depending on what you're actually replacing — a bulb, a standardized sealed beam, or a modern composite assembly. This is the full size reference: the standardized round and rectangular lamp dimensions in inches and millimetres, how to measure a headlight correctly, and why modern assemblies have no size at all — only a part number.
GuideHeadlight Bulb Size Reference Chart (H11, 9005, 9006, H7, H4, 9012 & More)
A quick-reference headlight bulb size chart — base code, beam type, common positions, and typical vehicle use for H11, 9005, 9006, H7, H4, 9012, H13, D-series HID and more, so you buy the right fitment the first time.
GuideHeadlight Bulb Cross-Reference & Interchange Guide: Which Bulbs Are Interchangeable?
H4, 9003, HB2 are the same bulb — 9005 and 9006 are not. A plain-English cross-reference for headlight bulb numbers: alternate names, which bulbs physically interchange, how to find your LED or OEM equivalent, and how to identify the bulb you have. Applies to any car, truck, or SUV.
GuideChoosing Headlight Bulb Sizes: H11 vs 9005, H7, H4 & More
How to find the right headlight bulb size for your vehicle — what H11, 9005, 9006, H7, H4, and 9012 mean, single vs. dual beam, and how to avoid buying the wrong bulb.
How the parts work — anatomy & reference
What each piece of a lighting system does, how it fails, and which piece you replace when it does — front housing, rear housing, and every other lamp on the vehicle.
Parts of a Car Headlight: Anatomy & Components Explained
A headlight isn't one part — it's an assembly of a housing, lens, reflector or projector, a bulb, and sometimes a ballast, halo, and wiring harness, all held in aim by tiny adjuster screws. Here's every component of a modern car headlight, what each one does, how they fail, and which piece you actually need to replace when something goes wrong.
GuideCar Light Parts: Every Light on Your Vehicle, Explained
A modern car carries around twenty separately-regulated lighting positions — and most drivers can name three. This is the complete reference: every exterior and interior lamp position, what each one legally has to do, the bulb numbers each typically takes, and the non-bulb parts (sockets, harnesses, flasher relays, ballasts, control modules) that fail far more often than people expect.
GuideTail Lights Explained: Bulb Sizes, LED Upgrades & Replacing an Assembly
One red housing at the back of your car does four different jobs — tail, brake, turn, and reverse — and each one runs a different bulb. Here's the full tail-light bulb size reference (1157, 3157, 7443, 921, 194), which numbers interchange and which only look alike, why LED turn signals hyperflash and how to stop it, and when to replace the whole assembly instead of a bulb.
GuideProjector vs. Reflector Headlights: Which Housing Actually Lights the Road Better?
Projector and reflector headlight housings shape light in completely different ways — and it changes your beam pattern, your glare, and how well an LED upgrade actually works. Here's how each one works, how to tell which you have, and how to choose the right housing (or the right bulb for the housing you've got).
Choosing an upgrade
Deciding between technologies, colour temperatures, and repair-vs-replace before you spend anything.
LED vs HID Headlights: Which Upgrade Is Right for Your Vehicle?
LED or HID/xenon? How the two headlight upgrades really differ — brightness, beam pattern, color temperature, lifespan, install effort, and which fits your vehicle best.
GuideHeadlight Color Temperature Explained (3000K, 4300K, 5000K, 6000K–6500K & 8000K)
What headlight color temperature actually means in Kelvin, how 3000K amber to 8000K blue looks on the road, and which color temp gives the best real-world visibility for LED and HID headlights, fog lights, and driving in rain, snow, and fog.
GuideSealed Beam Headlight Upgrade Guide (7-Inch Round, 5x7/7x6 & 4x6 LED Replacements)
How to upgrade old sealed beam headlights to modern LED — the 7-inch round, 5x7/7x6, and 4x6 rectangular size families, which vehicles use each, DOT/legality, wiring, and how to buy the right fitment the first time.
GuideHeadlight Restoration vs. Replacement: When to Polish Hazy Housings and When to Swap Them
Cloudy, yellowed headlights kill your night visibility and your resale value. Here's how to decide between restoring the hazy lens and replacing the whole housing — what restoration actually fixes, when it won't hold, and how to buy the right replacement (new LED assembly or used OEM) the first time.
Install, aim & troubleshoot
The work after the box arrives — fitting the bulb, re-aiming the beam so you are not blinding traffic, and fixing flicker or bulb-out errors when they show up.
How to Install LED Headlights: Step-by-Step for Any Vehicle
A clear, vehicle-agnostic guide to installing LED headlight bulbs or conversion kits — tools, wiring, anti-flicker fixes, beam aiming, and avoiding glare.
GuideHow to Aim Your Headlights: The 25-Foot Wall Method
New LED bulbs or a fresh assembly and now you're blinding oncoming traffic — or lighting the treetops instead of the road? Any bulb or headlight swap moves your beam. Here's how to re-aim it properly with nothing but a wall, a tape measure, and ten minutes: the 25-foot method, the low/high-beam split, and the exact heights that keep you legal and glare-free.
GuideHow to Fix LED Headlight Flicker & Bulb-Out Error Codes (CANbus, Decoders & Harnesses)
Your new LED headlights flicker, strobe at startup, or trigger a 'bulb out' warning on the dash. Here's why it happens — CANbus bulb-detection and underpowered circuits — and the exact fix ladder: CANbus-ready bulbs, anti-flicker decoders, load resistors, and relay harnesses, matched to your symptom.
GuideAre LED Headlights Legal? A Plain-English, Region-by-Region Overview
LED headlights sit in a legal gray zone: a factory LED assembly is fully legal, but dropping LED bulbs into a halogen housing is a different question entirely. Here's what the law actually says in the US, Canada, the UK/Europe, and Australia — and how to upgrade in a way that keeps you road-legal and out of glare-complaint territory.
Once you know the fitment: the ranked lists
The guides above tell you what fits. These pick through what's actually available and rank it, with a "Check Price on Amazon" link on each pick.
Best LED Headlight Bulbs for Reflector Housings
Top ListBest Fog Lights for Cars, Trucks & SUVs
Top ListBest Halo Projector Headlights
Top ListBest LED Headlight Conversion Kits
RoundupBest LED Light Bars for Trucks, Jeeps & SUVs
Chasing a housing for an older or lower-volume vehicle? New aftermarket assemblies often don't exist for it. Used and OEM pulls, matched by factory part number, are on eBay Motors — see the size guide's interchange-identity checklist before you buy one.
Browse OEM headlight assemblies on eBay