T8 vs T12 LED Bulbs: Which Tube Light Saves More Energy & Money?
T8 and T12 LED bulbs are fluorescent-length tubes that use LED chips instead of gas; the “T” means tube and the number is eighth-inch diameter, so T8 is 1 inch, T12 is 1.5 inches.
Walk into any old office or garage and you’ll likely see the fatter T12 still glowing, while newer fixtures come with slim T8. Most people never notice the label, they just ask for “the long white light” and end up with whatever the store clerk grabs.
Key Differences
T8 LED runs on 18–22 watts, T12 on 28–40 watts for the same 4-foot length. The slimmer T8 delivers 2,200–2,600 lumens, the older T12 peaks around 2,000. T8 uses electronic ballasts or direct-wire drivers, T12 still relies on magnetic ballasts that hum and flicker. In short, T8 produces more light for roughly half the power and lasts 50,000 h vs 30,000 h for most T12 LEDs.
Which One Should You Choose?
If your fixture has a T12 tombstone, retrofitting with a plug-and-play T8 LED saves up to 50 % energy and eliminates ballast buzz. For new installs, pick T8 for tighter spacing and lower cooling load. Only choose T12 if you’re forced to reuse existing magnetic ballasts and even then, consider a ballast-bypass T8 to cut lifetime costs.
Can I put a T8 LED into an old T12 fixture?
Yes, but either use a plug-and-play T8 that tolerates magnetic ballasts or rewire to bypass the ballast for best savings.
Does the smaller T8 give less light?
No. Despite the thinner tube, a quality T8 LED emits 10–30 % more lumens while using fewer watts.
How much money will I save?
Running a 20 W T8 LED for 10 h a day at $0.12/kWh costs $8.76 per year, versus $17.52 for a 40 W T12, saving roughly $9 per tube annually.