Corn Cob LED Bulbs: Replacing Metal Halide and HPS Lamps in Existing Fixtures
What corn cob LED bulbs are, which wattage replaces 100–400 W metal halide and HPS lamps, E27 and E40 bases, ballast bypass, heat in enclosed fixtures, and when a full LED fixture is better.
Key points
- Corn cob LED bulbs have LEDs around a cylinder and screw into the existing E27 or E40 socket, replacing HID lamps without changing the fixture.
- Typical swaps: 30–40 W LED for 100–150 W metal halide, 50–60 W for 175 W, 80–100 W for 250 W and 120–150 W for 400 W.
- Most require bypassing the ballast; the fixture must then be labelled so nobody fits an HID lamp again.
- Heat is the weak point in enclosed fixtures; choose bulbs with a fan or a design rated for enclosed use, or replace the fixture.
Corn cob LED bulbs are a shortcut: keep the old street lantern, high bay or wall pack, take out the metal halide or sodium lamp, and screw in an LED. For sites with many sound fixtures and a tight budget, they can cut energy by 60–70% in an afternoon. They also have limits that buyers should know before ordering hundreds.
What a corn bulb is
- LEDs mounted on all sides of a cylinder or polygon, giving 360° light
- A built-in driver in the base or the core
- An aluminium heat sink, sometimes with a small fan
- A standard base: E26/E27 (medium) or E39/E40 (mogul)
They are used in post-top lanterns, acorn lights, older street lights, high bays, wall packs, canopy lights and some floodlights.
Wattage equivalents
| Old lamp | Power with ballast | Typical corn bulb |
|---|---|---|
| 70 W HPS / MH | about 85–90 W | 20–30 W |
| 100–150 W MH | about 120–180 W | 30–40 W |
| 175 W MH | about 210 W | 50–60 W |
| 250 W MH / HPS | about 290 W | 80–100 W |
| 400 W MH / HPS | about 450 W | 120–150 W |
For fuller tables, see the HPS to LED conversion chart. Corn bulbs usually need a little more wattage than a full LED fixture for the same ground light, because 360° light is lost in the old reflector.
Bases and sizes
| Base | Typical lamps | Notes |
|---|---|---|
| E26 / E27 | 50–175 W HID, post-tops, wall packs | Medium screw |
| E39 / E40 | 250–1000 W HID, street lights, high bays | Mogul screw |
Check the physical size: high-power corn bulbs are long and heavy. Measure the space inside the lantern or reflector, and check that the socket and its mounting can hold the weight, especially if the lamp hangs base-up.
Ballast bypass
Most corn bulbs run directly on 100–277 V mains:
- Isolate the circuit
- Disconnect or remove the ballast, ignitor and capacitor
- Connect line and neutral directly to the socket
- Fit a label inside the fixture: “LED only, ballast removed”
Leaving the ignitor in circuit can destroy an LED bulb immediately, because it produces high-voltage pulses. If the fixture is ever re-lamped with HID, the lamp will not work without a ballast; the label prevents mistakes.
Some bulbs are “ballast compatible”. They are quicker to install but depend on the old ballast, which may be near end of life and wastes energy.
Heat in enclosed fixtures
LEDs dislike heat. An HID lantern is designed to get very hot; an LED driver in the same space can fail early.
- Choose bulbs rated for enclosed fixtures
- Fan-cooled bulbs move air but the fan itself can fail
- Check the ambient temperature range on the datasheet
- In very hot climates or sealed lanterns, a full LED fixture or an LED module retrofit kit is more reliable
Light distribution
HID reflectors were designed for a small, bright point source. A corn bulb is a large cylinder of light:
- In post-top lanterns and acorn globes, 360° light works well
- In street lights with a flat lens, much light hits the housing and the ground pattern changes
- In high bays with reflectors, results vary; some corn bulbs have a directional “half” design
Always test one fixture at night before converting a whole site.
When to choose corn bulbs, kits or new fixtures
| Situation | Best option |
|---|---|
| Decorative post-tops and lanterns in good condition | Corn bulbs |
| Old street lights with sound housings, limited budget | Corn bulbs or LED retrofit kits |
| Fixtures with cracked lenses, corroded housings | New LED fixtures |
| Sites needing dimming or smart controls | New LED fixtures |
| High bays above 8 m | New LED high bays for better optics |
For street lights, our modular LED street lights replace whole heads; for warehouses, LED high bays do the same. For small sockets, our LED bulbs cover 5–12 W household lamps, and we supply high-power corn lamps through our partner factory for retrofit projects.
Savings
Take 100 post-top lanterns with 150 W metal halide (about 180 W with ballast) replaced by 40 W corn bulbs, 12 hours a night at US$0.15/kWh:
- Saving: 140 W × 100 × 4,380 h ≈ 61,300 kWh a year
- About US$9,200 a year, plus fewer lamp changes
Run your own figures in the LED retrofit savings calculator.
Quality checks
- Real lumens and efficacy (lm/W) from a test report
- Driver quality and power factor above 0.9
- Surge protection for outdoor use
- Rated ambient temperature and enclosed-fixture rating
- Weight and length compared with your fixtures
- Colour temperature: 3000K for residential and heritage areas, 4000–5000K for industrial and car parks
- Warranty of at least three years
Safety
Converting fixtures can change their certification. In some markets, a retrofit must follow the bulb maker’s instructions and be labelled to remain compliant. Never use standard corn bulbs in hazardous areas; explosion-proof fixtures must be replaced with certified ones.
Ordering
Send photos of the existing fixtures, the lamp wattage and base, the number of units and the climate. We will suggest corn bulbs, retrofit kits or new fixtures for each type.
Sources
Frequently asked questions
What is a corn cob LED bulb?
A high-power LED lamp shaped like a cob of corn, with LEDs on all sides of a cylinder. It fits the E26/E27 or E39/E40 sockets of existing street lights, post-top lanterns, high bays and wall packs to replace metal halide, sodium or mercury lamps.
Do corn bulbs need a ballast?
Most corn bulbs run directly on mains voltage, so the ballast, ignitor and capacitor are removed or bypassed. Some models are ballast-compatible, but direct wiring is usually more reliable and efficient.
Are corn cob LED bulbs bright?
They can be very bright, but their 360° light suits fixtures with reflectors designed for HID lamps. In fixtures that need downward light, a full LED fixture often puts more light on the ground for the same watts.