S14, G40, ST38 and G45: string-light bulb shapes explained
A shape code names the bulb's envelope and its nominal size, and nothing else. iLamp Technology (Shenzhen iLamp Technology Co., Ltd) builds its socketed string ranges in S14, G40 and ST38, and its bulb range carries S14 and G45 bulbs on their own. Once the shape is fixed, the length, the socket count, the cable and the plug decide the product.
How a shape code reads
Each code has two parts: letters for the envelope shape, and a number for its nominal size within that shape family. That is all it fixes. Wattage, colour temperature, base, dimming and the material of the envelope are separate lines on a specification, and they are the lines a quotation has to pin down.
One envelope can carry more than one code, and two bulbs of the same size need not match. The bulb range carries two 45 mm bulbs in this shape, one named S14 and one named ST45, on different specifications: the S14 bulb is 45 × 85 mm on an E27 base, 2 W and 150 lm at 2700 K, listed as not dimmable; the ST45 bulb is 45 mm on an E26/E27 base, 2 W at 180–220 lm, listed as dimmable. G45 is 45 mm on an E26/E27 base: 2 W at 180–220 lm, 4 W at 350–450 lm, and a frosted 4 W at 280–320 lm, all dimmable.
Those bulb figures are as listed by the factory (2015–2020 data); the current model and its figures are confirmed on your quotation. No envelope size is published for G40 or ST38, so ask for the bulb drawing with your quotation.
The four shapes side by side
| Specification | S14 | G40 | ST38 | G45 |
|---|---|---|---|---|
| Sold as | Mains strings at 120 V and at 230 V; solar strings; bulbs on their own | Mains strings at 120 V; solar strings; one smart WiFi and RGBW string | Mains strings marked 120/240 V and 120/230 V; solar strings | Filament bulb, quoted by the piece |
| Bulb envelope | S14 bulb 45 × 85 mm, base E27 | Ask for the bulb drawing | Ask for the bulb drawing | 45 mm across, base E26/E27 |
| Mains lengths | 24 ft / 7.3 m · 48 ft / 14.6 m · 100 ft / 30 m | 25 ft / 7.6 m · 50 ft / 15.2 m · 100 ft / 30 m | 50 ft / 15 m · 100 ft / 30 m | — |
| Sockets per length | 24 ft: 12 · 48 ft: 15 · 100 ft: 30 | 25 ft: 10 or 25 · 50 ft: 25 · 100 ft: 50 | 50 ft: 15 or 25 · 100 ft: 50 | — |
| Cable | 18 AWG or 20 AWG SJTW at 120 V; 0.75 mm² or 1.0 mm² at 230 V | SPT-1W | SPT-1 | — |
| Socket type | Suspension or die-casting | Ask for the socket type | Suspension | — |
| Plug | US 2 Prong · EU 2 Round F · GB 3 G | US 2 Prong | Marked 120/240 V or 120/230 V; the plug is confirmed on your quotation | — |
| Dimming | The S14 bulb is listed as not dimmable; name dimming on your enquiry | Ask on your enquiry | Ask on your enquiry | Dimmable |
| Indicative price | US$14.5–29.4 per string | US$6.5–14.9 per string | US$10.2–15.8 per string | Quoted by the piece |
Bulb figures are as listed by the factory (2015–2020 data); the current model and its figures are confirmed on your quotation. String figures are the factory's 2025 specification. Indicative prices are ex-works, before freight and tax, on the factory's Sep 2026 list price plus 20 %; the exact price is confirmed on your quotation.
Solar and smart strings use the same shapes
The shapes are not limited to mains strings. Solar S14 runs at 25 ft / 7.6 m with 8 sockets, 48 ft / 14.6 m with 15 and 100 ft / 30 m with 30. Solar G40 runs at 25 ft / 7.6 m with 10 sockets, 48 ft / 14.6 m with 18 and 50 ft / 15 m with 25. Solar ST38 runs at 50 ft / 15 m with 25 sockets and 100 ft / 30 m with 50. Panels come at 1.5 W, 3 W and 5 W against those models. One smart WiFi and RGBW string carries a G40 code, at 25 ft / 7.6 m with 25 sockets; the other smart references carry a different bulb code, so ask which bulb goes in them.
Socket count and spacing
Every string is specified by its length and its socket count. The spacing between sockets is not given, so divide the one by the other for a first estimate, and remember that the same length is offered with more than one count: a 25 ft / 7.6 m G40 string comes with 10 sockets or with 25, and a 50 ft / 15 m ST38 string with 15 or with 25. Before you write an installation sheet or size a carton, have the exact socket positions, the lead-in length and the tail confirmed on your quotation.
Which shape for which job
G40 and ST38 cover distance for the money. Both take SPT cable, both reach 50 sockets on a 100 ft / 30 m run, and both start below S14 on the indicative ranges above. S14 is the one to specify when the bulb itself is part of the look: it takes SJTW cable in 18 AWG or 20 AWG at 120 V and 0.75 mm² or 1.0 mm² at 230 V, it is the only one of the three offered with a choice of suspension or die-casting sockets, and it is the only one offered with EU and UK plugs as well as US. G45 is for supplying bulbs rather than strings: a pendant, a fixture, a replacement line.
Dimming is set per bulb, not per shape. Both G45 wattages are listed as dimmable. Of the two 45 mm bulbs above, the ST45 one is listed as dimmable and the S14 one is not, and nothing is published either way for G40 or ST38. Name dimming on your enquiry and have the bulb and the dimmer confirmed together on your quotation; the dimmable filament bulb guide covers what the word has to mean on a specification.
Patios and terraces, café and restaurant frontages, event and wedding hire stock, and permanent commercial runs all take the same three string shapes. What changes between them is the length, the socket count and how often the string is rigged and taken down. The market rules follow the voltage and the use, not the bulb shape: the seasonal and all-year guide covers the United States, and the CE and energy-label guide covers the EU and the UK. Which documents to ask for, family by family, is set out in documents and certification.
What still has to be specified
- Market and voltage. 120 V or 230 V, with the matching plug: US 2 Prong, EU 2 Round F or GB 3 G.
- Length and socket count. Both are set per model, and the same length is offered with more than one count.
- Cable. SPT-1 or SPT-1W on G40 and ST38; SJTW in 18 AWG or 20 AWG on S14 at 120 V, and 0.75 mm² or 1.0 mm² at 230 V. Black and white cable are both offered.
- Socket type. Suspension or die-casting on S14, suspension on ST38; ask for the socket type on G40.
- Power. Mains, a solar panel at 1.5 W, 3 W or 5 W, or WiFi and remote control on the smart references.
- The bulb. Envelope material, colour temperature, dimming and diameter are not given against every model. Name what you need on the enquiry and have it confirmed on your quotation.
- Anything off the table. Lengths, socket counts, plug types, cable and retail packaging are made to order, and private label is offered: see OEM and private label.
What to check on your sample
- Count the sockets and measure the run against the length and socket count quoted for that reference.
- Fit a bulb in the first socket and the last one, and check that it seats square and holds.
- Read the print on the cable: gauge and type, against the model you asked for.
- Check the plug against the market you sell into, and check the cable colour against your packaging artwork.
- If the bulbs are dimmable, dim them on the dimmer you intend to sell alongside them, at the bottom of the range as well as the top.
- Weigh and measure the inner box against the figures quoted for the model, because your freight quote is built on them.
Limits of these figures
Bulb figures here are as listed by the factory on 2015–2020 data, so the current model and its figures are confirmed on your quotation. Of these four shapes, an envelope size is given for the S14 bulb and for G45 only. Socket spacing, IP rating and envelope material are not given against the string models, so ask for all three with your quotation. Indicative prices are per string and move with length, socket count, plug and cable. Every figure here is confirmed on your quotation before it goes on an order. Reviewed September 2026.