Convert a 4ft fluorescent fixture to LED by either swapping in a plug-and-play LED tube (Type A, no rewiring, under 2 minutes) or bypassing the ballast and wiring a Type B LED tube directly to line voltage (15-20 minutes of basic electrical work).
A 4ft LED T8 tube draws 15-18 watts versus 32 watts for the fluorescent tube it replaces, saving approximately 50% on energy while producing equal or greater brightness. Both methods produce instant-on, flicker-free light with better color rendering than fluorescent.
The 4-foot T8 is the most common fluorescent tube in North America, used in millions of garage, workshop, office, and kitchen fixtures. Converting these fixtures to LED is one of the simplest and most cost-effective energy upgrades available.
Method 1: Plug-and-Play (Type A) - No Rewiring
Turn off the light switch. Rotate the existing fluorescent tube 90 degrees and slide it out of the tombstone sockets. Slide the new Type A LED tube into the same sockets and rotate to lock. Turn the switch back on. The LED tube powers through the existing ballast with no modifications. This method takes under 2 minutes per tube and requires zero electrical knowledge.
Before buying, open the fixture cover and find the ballast label. Check the LED tube's ballast compatibility list (printed on the packaging or available on the manufacturer's website). Type A tubes work with most instant-start electronic ballasts made after 2000. They are not compatible with older magnetic ballasts or programmed-start ballasts. If your ballast is not compatible, use Method 2.
The downside of Type A is that the ballast remains in the circuit, consuming 3-8 watts of electricity and serving as a future failure point. When the ballast eventually dies, you will need to either replace it or switch to Method 2. For a quick upgrade with minimal effort, Type A is excellent. For maximum long-term efficiency, Method 2 is preferred.
Method 2: Ballast Bypass (Type B) - Simple Rewiring
Step 1: Turn off the circuit breaker (not just the switch). Confirm power is off with a non-contact voltage tester. Remove the fluorescent tubes and the fixture diffuser cover.
Step 2: Locate the ballast - a rectangular box, usually 8-12 inches long, wired between the tombstone sockets. Cut all wires going from the ballast to the tombstones. You can remove the ballast (unscrew the mounting screws) or leave it disconnected in place.
Step 3: Connect the incoming hot wire (black) and neutral wire (white) directly to the tombstones. For single-end powered Type B tubes, both hot and neutral connect to the tombstones on ONE end of the fixture. For double-end powered tubes, hot goes to one end and neutral to the other. Check the LED tube packaging for the specific wiring diagram.
Step 4: Secure all connections with wire nuts. Wrap each nut with a layer of electrical tape. Affix a warning label: "Ballast Bypassed - LED Tubes Only." This prevents someone from accidentally installing a fluorescent tube in the modified fixture, which could cause arcing or breakage. Install the Type B LED tube, replace the diffuser cover, and restore power at the breaker.
LED Tube Specifications for 4ft Fixtures
Specification | Fluorescent T8 | LED T8 Replacement |
|---|---|---|
Wattage | 32W | 15-18W |
Lumens | 2,800 | 2,200-3,200 |
Color Temperature | 4100K (cool white, fixed) | 3000K-6500K (your choice) |
CRI | 75-85 | 80-95 |
Lifespan | 20,000-30,000 hrs | 50,000+ hrs |
Warm-up Time | 30 sec - 3 min | Instant |
Mercury | Yes (~4 mg) | None |
Choosing Between Type A and Type B
Use Type A when you want the fastest possible conversion with zero electrical work and your ballast is compatible. Use Type B when your ballast is old, magnetic, or not on the compatibility list; when you want to eliminate the ballast's energy waste; or when you want a maintenance-free installation with no future ballast replacements.
In commercial settings with many fixtures, Type B is the standard recommendation because the cumulative ballast energy savings and eliminated maintenance costs are substantial over the fixture's lifetime.
Frequently Asked Questions
Can I use a 4ft LED tube in a T12 fluorescent fixture?
LED T8 tubes (1-inch diameter) fit in T12 fixtures (1.5-inch diameter) because they share the same G13 bi-pin base. The LED tube is slightly thinner but the pins lock into the same tombstone sockets. If your T12 fixture has a magnetic ballast, use a Type B ballast-bypass LED tube because Type A tubes are generally not compatible with magnetic ballasts. The conversion is identical to the steps described above.
How much money does converting to LED save?
Converting one 4ft fixture (two tubes) from fluorescent to LED saves about 30 watts per fixture. Running 12 hours per day at $0.16/kWh, that saves approximately $21 per fixture per year. A garage with four fixtures saves $84 annually. A small office with 20 fixtures saves $420 annually. The LED tubes typically cost $5-$10 each, so the payback period is 3-8 months depending on usage.
Do I need to replace the tombstones when bypassing the ballast?
For non-shunted tombstones (two separate electrical contacts), no replacement is needed - they work with both single-end and double-end powered LED tubes. For shunted tombstones (both contacts connected internally), you may need to replace them with non-shunted versions if using single-end powered Type B tubes. Non-shunted tombstones cost $1-$2 each and snap into the same mounting holes. Check the LED tube instructions for the specific tombstone requirement.
