Dimmable LED filament bulbs: what dimmable means, which dimmers, and what to test
Dimmable is a field on the bulb's own table, not a promise about the wall dimmer in your market. It means iLamp Technology (Shenzhen iLamp Technology Co., Ltd) prints the bulb as dimmable and, on most models, names the one dimmer it was tested on. Your dimmer type, your bulb count and your circuit decide the rest.
What the bulb table prints
Each bulb table is the specification as listed by the factory (2015–2020 data); the current model and its figures are confirmed on your quotation. Four printed fields decide a dimming question.
| Field | What is printed | How to read it |
|---|---|---|
| Dimmable | Yes on 69 models, No on two, absent on three | Read it per model, never per shape. The two models printed as not dimmable are an A60/A19 milky bulb and an S14 bulb. |
| Dimmer tested | On 68 models; 66 of them name the Lutron Diva DVELV-300P / DVCL-153P | One dimmer, named by the factory. It is not a compatibility list and not a conformity document. |
| Power factor | On 31 models: >0.8 on 20 of them, >0.85 on 11 | Ask for it when many bulbs sit on one circuit, or where your market asks for the figure. Where a table prints none, ask with your quotation. |
| CRI | On all 74 models: >80, >90, or ">80 or 90" where both grades are listed | Colour rendering, not dimming. Check the colour of the sample low on the dial as well as at full output. |
Forward-phase and reverse-phase dimmers
General guidance, not a statement about any model. A mains wall dimmer cuts part of every half-cycle of the supply. Forward-phase types, usually triac-based and sold for incandescent and halogen loads, cut the start of the half-cycle. Reverse-phase types, often described as trailing-edge or electronic, cut the end of it and are usually easier on the small driver built into a filament bulb. The dimmer the factory names is an electronic type.
Every dimmer also states a minimum load in its own instructions. A few low-wattage filament bulbs on one dimmer can draw less than that minimum, and a dimmer under its minimum load can flicker, buzz or refuse to start, with nothing wrong in the bulb. That is why the bulb count belongs in the sample test and not only in the order.
What changes the answer
| Variable | Why it changes the result | What to do |
|---|---|---|
| Dimmer type | Forward-phase and reverse-phase dimmers drive the bulb's driver differently. | Find out which type your installer or your customer will fit, and test that type. |
| Minimum load | A dimmer states its own minimum load; a small number of low-wattage bulbs can fall below it. | Read the dimmer's instructions, then test with the bulb count you will actually sell. |
| Bulb count and mixed loads | A filament bulb sharing a dimmer with other lamp types changes the load the dimmer sees. | Test the circuit as it will be built, not a single bulb on a bench. |
| Mains band | Only 13 of the models print a voltage entry; those that do print AC110-130V / 220-240V, or one band on its own. The dimmer and the bulb have to be built for the same band. | Have the mains band of the sample and of the production order written on your quotation. |
| The model itself | Dimmable is printed per model, and three tables print no dimmable entry at all. | Quote the ILT reference and the factory code, and read that model's own table before you order. |
Which bulbs this covers
The shapes with a dimmable entry run across C35, C32, C22, C7, A60/A19, ST64, ST58, ST45, G45, G80, G95, G125, T30, T20/T25/T45, P45, spiral filament and G4 / G9, on E26/E27, E12/E14, B22, B15, G9 and G4 bases. Shape does not decide the answer: two models print Dimmable: No and three print no dimmable entry, so the model table is the only place to read it. The factory's own descriptions offer many of these shapes in dimmable and non-dimmable versions, so name the version you want on the enquiry. The bulb shapes guide explains how the shape codes read.
Five checks to run on your sample
Run all five with the dimmer you will sell into, not with a bench supply. Write the results into your acceptance note so the same checks can be repeated on the production batch.
Dim to the bottom
Take the dial down to roughly a tenth of full output. Note the point where the bulb drops out, jumps or goes dark, and whether it comes back cleanly when you raise it.
Look for flicker
Point a phone camera at the bulb at full output and again low on the dial. Rolling bands or a stutter on screen show flicker the eye may miss. Repeat in the camera's slow-motion mode.
Listen for buzz
In a quiet room, listen at the bulb and at the dimmer through the whole range. A buzz that appears only in part of the range usually points at the pairing of dimmer and load.
Start from cold
Switch on at the lowest setting from cold. Note any delay, any jump to full output, and any bulb that will not start until the dial is raised. Repeat after an hour of warm-up.
Test the real circuit
Repeat the first four checks with the number of bulbs, the mix of lamp types and the dimmer of the actual installation. Minimum load is a property of the circuit, not of one bulb.
Documents to ask for
A tested-dimmer entry is a specification line, not a conformity document. For the compliance side of a bulb order: the factory states a UL file for its LED filament bulbs, so ask for the current listing card for the exact model. The factory also states CE and RoHS marking, self-declared; the declaration of conformity and the test reports are requested per model and will be published here when received. Until then, ask for them with your quotation and treat the marks as the factory's statement. The documents and certification register sets out what exists per family and per market, and the CE and energy labels guide explains which EU and UK rules decide the paperwork.
What the tested dimmer does not cover
The factory names one dimmer. That is not a statement about any other dimmer, on any model, in any market. The printed figures are 2015–2020 data, so the current model, its power factor and its dimmable entry are confirmed on your quotation before you order. Reviewed September 2026.
Questions buyers ask
Does dimmable mean the bulb will dim on my dimmer?
Which dimmer did the factory test?
Why does a dimmer flicker or buzz with only two or three bulbs on it?
Can I order the same shape in a non-dimmable version?
Ask for a dimmable sample
Send the shape, the base, the mains band and the dimmer you will sell into. The quotation names the exact factory code and configuration, a sample follows, and your acceptance checks decide whether the order runs. The samples and ordering page sets out the full sequence.