How to link several grow light bars to one timer
Linkable bars chain together so one plug feeds all of them. Then one timer controls the lot, if the total watts are within limits.
What linkable means
Linkable bars have an output socket, and a short connecting cord joins one bar to the next. As published limits: Barrina lists its 4-foot, 20 W ML20 as linkable up to 8 lamps in series, and its 2-foot, 10 W MF10 as linkable up to 16 lamps. Other brands have their own limits, so follow your fixture's manual.
Add up the watts
| Setup | Total watts |
|---|---|
| 2 x 4-foot bars at 20 W | 40 W |
| 4 x 4-foot bars at 20 W | 80 W |
| 8 x 4-foot bars at 20 W (the published limit) | 160 W |
| 8 x 2-foot bars at 10 W | 80 W |
| 16 x 2-foot bars at 10 W (the published limit) | 160 W |
The watts per bar are the published figures for those two Barrina models. Use the watts printed on your own fixtures.
Check the timer
- Read the rating on the timer's label. It is given in amps, watts or both. Watts equal volts times amps, so a 15 amp timer on a 120 volt outlet is rated for up to 1,800 W by that arithmetic, but trust the label on your timer, because some timers have lower limits for certain loads.
- Keep the total watts of everything on the timer well under the label figure.
- Set the hours. See hours per day. Most sources say 14 to 16.
- If a heat mat shares the shelf, it often needs its own plug or thermostat. See the heat mat guide.
If you use a power strip
Treat the strip's rating the same way. Do not chain strips together.
Sources
- Barrina: T5 20W LED grow light 4FT 5000K (ML20), manufacturer page
- University of Illinois Extension: Starting the garden, supplemental lighting for indoor seed starting (2020)
- Utah State University Extension: Starting vegetable seeds indoors, seeding culture and transplanting (2025)