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Published October 25, 2026 · Last updated October 25, 2026 · 7-9 min read · Procurement Guide

Wireless Charging Lamp OEM: How the Coil Is Specified Before Tooling Starts

Which coil is being specified — the one charging the phone, or the one inside the lamp?

Most wireless charging lamps contain a transmitter coil in the base and no coil in the lamp body; cordless lamps invert this, carrying a receiver coil that charges from a dock.

These are two different products with two different specification documents, and first-time buyers regularly sign off on the wrong one. Before anything else, decide which of the three architectures below you are actually building.

Architecture A: a mains-powered lamp with a charging pad built into the base

The lamp plugs into the wall. A transmitter coil, its driver IC and a ferrite shield sit inside the base or a cantilevered arm, and the user drops a phone onto the marked window. The coil spec is a coil-plus-driver spec: inductance, Q, DCR, ferrite grade, foreign object detection (FOD) thresholds, and the thermal path between the coil and the LED heat sink that shares the same housing.

Architecture B: a cordless lamp that is itself charged on a dock

The lamp carries the receiver coil and a small lithium cell; the transmitter lives in the dock. Here the spec is coil-plus-battery: receiver inductance, alignment tolerance across the whole foot of the lamp, charge current profile, cell temperature during charge, and what happens when the lamp is set down slightly off-centre. Cordless lamps in this category are industry-typically specified at 5W class, because 15W into a small cell in a sealed foot is a thermal problem, not a coil problem.

Architecture C: both, in the same product

A lamp that charges a phone and also charges itself on a base is a legitimate and popular design, and it is the hardest to specify. You now need two coils, two thermal budgets, and a physical keep-out between them so that the lamp's own receiver does not pick up the transmitter field. Industry-typical layouts push the two coils to opposite ends of the base and add a small shielding can between them.

The rule of thumb: Architecture A is a coil-and-driver spec, Architecture B is a coil-and-battery spec, Architecture C needs both plus a coupling test in the validation plan. Nothing downstream — housing, tooling, packaging copy — is safe to start until that choice is locked.

What coil parameters actually go on the specification sheet?

Six parameters carry the design: inductance, Q factor, DC resistance, physical geometry, ferrite shielding and termination — everything else on the drawing is derived from those.

A coil drawing that lists only "Qi coil, 15W" is not a specification, it is a wish. Here is what a working drawing contains, with the ranges most factories in this category work to.

1. Inductance (Ls). Written as a nominal plus a window, measured at 100 kHz with a named LCR meter, named test leads, and — critically — with the ferrite shield in place. Industry-typical tolerance is ±5% for 15W and Qi2 designs and ±10% for 5W designs. The single most common spec dispute in this category is a coil measured bare on a bench versus the same coil measured in the assembly; the two readings differ, and the driver is tuned to the second one.
2. Q factor. Measured at the operating frequency, industry-typically somewhere in the 87–205 kHz band. Mature designs sit at Q ≥ 60 for 5W and Q ≥ 80 for 15W-class coils. Q is the number that tells you the Litz wire and the ferrite are genuinely good; DCR alone does not.
3. DC resistance. Industry-typically 100–350 mΩ for a lamp-base transmitter coil. Lower DCR means less self-heating, but a very low DCR with a thin Litz build or a poor ferrite grade will still fail on Q.
4. Geometry. Outer diameter, inner diameter, turn count, winding style (single layer, double layer or stacked) and wound height. On a lamp the charging window is usually dictated by industrial design first, so outer diameter is often the first number fixed and the last one negotiated.
5. Litz wire construction. Strand count and strand diameter, for example 0.08 mm × 80–105 strands, plus insulation type and the self-bonding layer. Writing "0.08 × 100" on the drawing is what stops a supplier substituting solid or coarser wire later.
6. Ferrite shield. Material grade, permeability, thickness (industry-typically 0.3–1.0 mm), tile count and bonding method, and Curie temperature. In a metal-bodied lamp this is the parameter that decides whether the coil works at all — more on that below.
7. Termination. Flying leads with stated length and strip length, or a wire-to-board connector; solder pad finish; strain relief where the lead exits the ferrite stack.
8. Thermal and sensing. Insulation class of wire and adhesive, plus the exact mounting position of the NTC thermistor relative to the coil. On a lamp base, an NTC placed on the driver PCB instead of near the coil reads the wrong temperature and lets the coil run hot.

Two document-control habits matter as much as the numbers. First, the coil drawing and the driver reference design must be versioned together — a coil change without a driver retune invalidates the FOD calibration. Second, the drawing should state the measurement fixture, because a coil is only "18 µH" relative to a defined test setup.

Should a lamp OEM target 5W baseline, 15W extended power, or Qi2 magnetic?

Choose the profile from the phone population you serve and the heat your lamp base can shed — not from the headline wattage.

The three mainstream options look similar on a spec sheet and behave very differently inside a lamp.

5W baseline power profile

Cheapest coil, thinnest ferrite, loosest alignment tolerance, simplest driver and the lightest certification burden. It is the right choice for an ambient or bedside lamp where the phone charges overnight rather than at speed. Buyers who insist on 15W for a mood lamp usually end up paying for thermal headroom they never use.

15W extended power profile

Needs a better coil, a thicker ferrite, a driver that can do proper power-loss FOD, and a base that can shed roughly three times the heat. In a slim lamp base, the coil and the LED driver are competing for the same few cubic centimetres of air.

Qi2 magnetic power profile

Adds a magnet ring so the phone snaps into alignment, which removes the alignment problem that otherwise drives a lot of field complaints. It also adds cost, an assembly step, and a magnetic field that constrains where the LED driver, speaker or steel fasteners can sit. For a lamp meant to sit on a desk with a phone attached to it, the alignment benefit is real; for an overnight charging pad, it is often money you do not need to spend.

Those figures are industry-typical reference ranges drawn from established reference designs in this category, not published LIGHT BDB product specifications. Your final numbers come from the coil drawing and the validation batch, and they should be treated as provisional until FOD has been calibrated inside the actual housing.

How does an aluminium or steel lamp body change the coil specification?

Metal near the coil detunes it, absorbs field energy and heats up, so the spec has to fix a metal keep-out distance and a thicker ferrite shield.

Metal-bodied lamps are the most common source of "it worked on the bench" failures. The effects are predictable, and each one maps to a line on the drawing.

• Detuning. A conductive body close to the coil lowers the effective inductance and shifts resonance. The driver can usually retune, but at the edge of its range efficiency drops sharply and heat rises. Specify the metal standoff distance explicitly — industry-typical designs hold roughly 2–4 mm between the coil face and any metal, with a plastic window in between.
• Eddy-current heating. The metal does not just reflect field, it absorbs it. A 15W coil sitting a couple of millimetres from an aluminium base will warm that base, and the base is what the user touches.
• FOD false trips. Foreign object detection works by comparing expected and actual power loss, and a nearby metal body changes the baseline. FOD must be calibrated in the finished assembly, not on a bare coil, or the lamp will refuse to charge phones on some units and quietly overheat on others.
• Fasteners. A single steel screw passing through the field is worse than the aluminium housing around it. Specify non-ferrous fasteners within the coil keep-out zone and mark the zone on the mechanical drawing.
• LED driver noise. A lamp base packs an LED driver, sometimes a USB port and the coil into the same small volume. Switching noise in the coil's detection band can disturb the ping sequence that starts a charge. Physical separation and, where needed, a local shield are cheaper than a driver redesign later.
• Thermal stacking. The coil and the LED driver share an air volume. Specify the maximum ambient inside the base and test at it, not at room temperature on an open bench.

If the industrial design demands a fully metal shell, expect the charging window to become a plastic or glass insert, and expect the base to grow a few millimetres. Those are design consequences, not supplier failures, and they are much cheaper to accept at the sketch stage than after tooling.

What MOQ, sample turnaround and lead time should a first-time buyer expect?

For a Light & Mood platform lamp, MOQ starts at 100 pcs standard, 300 pcs white-label and 500–1,000 pcs for full ODM customisation.

A wireless charging lamp sits on the Light & Mood platform, so it inherits the lighter tier structure rather than the body-care tiers (500 pcs standard, 1,000 pcs white-label, 2,000–3,000 pcs ODM custom).

• 100 pcs — standard platform build, typically the fastest route to a first container and the sensible starting point for a brand testing the category.
• 300 pcs — white-label, with your branding on an existing platform housing and an existing coil design.
• 500–1,000 pcs — ODM custom, where the housing, the charging window and the coil geometry can be reworked to your design.
• Samples — 7–14 days, with the sample fee refundable against the purchase order.
• Production — 4–8 weeks from deposit to FOB Shenzhen for most SKUs.
• Warranty — 500 days limited, one of the longer terms in this category.
• Terms — T/T 30/70 or L/C at sight, FOB Shenzhen, and we work with your nominated forwarder.

One point worth knowing at the low end: because coil winding happens in-house at the Panyu component plant, a 100 pcs order with a non-standard coil is technically possible. It is not free, though — a new coil drawing carries fixture setup and a small validation batch, and the validation batch does not scale down with the order quantity. Many first-time buyers are better served by keeping the platform coil and changing only the housing and the charging window.

Where does the coil drive cost, and how do cheap coils fail in the field?

The coil assembly is a small share of the lamp bill of materials, but it is where thin quotes hide the failures buyers see six months after launch.

Cost in the coil stack comes from four places: the Litz wire build, the ferrite grade and thickness, the magnet ring if you chose Qi2, and the test time at the end of the line. Industry-typically, a 15W-class transmitter coil assembly with ferrite lands somewhere in the region of USD 1–2.50 at 10k volumes, and a Qi2 magnet ring adds a few tens of cents to under a dollar. Treat those as category-typical ranges for planning, not as a LIGHT BDB quotation.

The failure modes to watch for are consistent across this category:

• DCR creep. A cheaper wire build raises resistance, which shows up as a warm charging window and slower charging, not as an outright failure.
• Q drop from ferrite substitution. A thinner or lower-grade ferrite can hold inductance on the bench and still collapse efficiency in the housing.
• Ferrite cracking. Tiles crack in transit or during assembly, and a cracked tile passes a quick inductance check while failing FOD later.
• Adhesive creep. A lamp base that runs warm for eight hours a day is a hard environment for coil bonding. Specify the adhesive's temperature class, not just its peel strength.
• Batch drift. Inductance wandering ±10% between lots will break a tightly calibrated FOD threshold. Ask for coil-level L, Q and DCR data per lot, not just a certificate of compliance.
• Connector fretting. A lead that vibrates against a housing edge is a warranty claim waiting for month nine.

Three things are worth requesting in the quotation stage: per-lot coil test data, an FOD calibration report generated in the final housing, and a thermal soak at the maximum ambient you expect the lamp to live in. A supplier who cannot produce those three is selling you a coil, not a charging system.

What are the honest trade-offs and risks in wireless charging lamp OEM?

Wireless charging adds real cost, heat and certification overhead to a lamp, and it is not the right feature for every SKU.

It is worth saying plainly where the compromises sit.

• 15W in a slim base is a thermal compromise. Sometimes 5W or 7.5W is simply the better product, and the market will not punish you for it.
• Metal-bodied designs lose something. Usually a plastic or glass charging window the industrial design team has to accept, and a base that grows a few millimetres taller.
• Qi2 magnets cost money and constrain layout. They decide where the LED driver, the speaker and the steel fasteners can go, and that constraint arrives at the sketch stage or not at all.
• Certification is per-SKU. A new coil, a new base geometry or a new driver can each trigger retesting, and test-house fees in this category are industry-typically in the low thousands of USD per SKU — a real burden when the first order is 100 pcs.
• Low MOQ and custom coils pull in opposite directions. At 100 pcs the engineering and validation work is spread across very few units, so per-unit engineering cost is high. Reusing a platform coil and changing the housing is often the commercially correct answer.
• A 500-day warranty has consequences. It means coil ageing, adhesive life and connector wear are planned for at design stage rather than discovered in year two.
• Scope clarity. LIGHT BDB is a wellness-device ODM. These are home and lifestyle products, not regulated healthcare equipment, and we do not present them as anything else.

What we do bring to the coil question is vertical control: the Panyu component plant — 10,000+ sqm, 600+ staff, operated by our exclusive strategic manufacturing partner Fuli Electronics — winds auto-grade inductors, transformers and wireless charging coils and runs its own SMT, with a 3,000 sqm finished-product assembly base in Shenzhen and a Yangon overflow line at 5,000+ pcs/day. Design support sits in Hangzhou and Hamburg. That does not make a metal-bodied 15W lamp easy. It does mean the coil, the driver and the housing are validated by the same team instead of three suppliers pointing at each other.

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