Can I grow cannabis with household LED or CFL bulbs?

Q: Can I grow cannabis with household LED or CFL bulbs?

You can keep seedlings and clones alive under household LED or CFL bulbs, but you can't grow good flower with them. Seedlings need about 150–300 µmol/m²/s; flower wants 600–1,200 µmol/m²/s over the whole canopy, which takes roughly 25–40 W of efficient horticultural LED per square foot. A handful of household bulbs delivers a fraction of that, so yields are small and buds airy.

Short answer

Household LED or CFL bulbs will raise seedlings and clones (150–300 and 50–150 µmol/m²/s), but they can't grow good flower. Flower wants 600–1,200 µmol/m²/s across the canopy, which takes roughly 25–40 W of efficient horticultural LED per square foot. A few household bulbs give a fraction of that. Supported.

Why

Cannabis yield follows light. In a controlled trial, dry flower yield rose linearly from 116 g/m² at 120 µmol/m²/s to 519 g/m² at 1,800 ^[1]. Starve the plant of light and you get proportionally less, plus airy, stretched buds.

Household bulbs are designed to light a room for human eyes. They throw light in every direction, so most misses the plant, and intensity falls quickly with distance. Their total output is small: a 10–15 W bulb against a 100–150 W grow light for even a 2 × 2 ft space.

Efficacy matters too. Good horticultural LEDs exceed 2.5–3 µmol/J ^[2]; household bulbs aren't rated for photosynthetic photons at all, so you can't plan with them.

Cuttings need little light: about 100–150 µmol/m²/s at most while rooting, by horticultural guidance ^[3]. That's why household bulbs work for propagation.

The numbers

Stage	PPFD needed	Household bulbs?
Unrooted clones	50–150 µmol/m²/s	yes, close to the plants
Seedlings	150–300 µmol/m²/s	yes, for the first 2–3 weeks
Veg	300–700 µmol/m²/s	marginal, leggy growth
Flower	600–1,200 µmol/m²/s	no: small, airy yield
2 × 2 ft (0.36 m²) flower light	100–150 W efficient LED	—

What to do

Use daylight-white household bulbs for seedlings or clones only, 18 h a day.
Keep them close, and check leaves aren't heating up.
Move plants to a horticultural LED by veg.
On a tight budget, buy one small dimmable LED for a 2 × 2 ft space rather than many bulbs.
Check every bulb socket and cord is rated and dry.

Common mistakes

Flowering under a few CFLs and blaming the strain for airy buds.
Judging bulbs by lumens.
Daisy-chaining clamp lamps and extension cords.
Hanging bulbs so close they scorch leaves.

Full article: PPFD and DLI by stage
Why don't lumens matter for grow lights?
What wattage LED do I need for my tent?
Why are my buds airy?
Terms: T5 fluorescent · light intensity

Follow-up questions

Can I flower cannabis under CFLs?

You can flower cannabis under CFLs, but the yield will be small and the buds airy. Flower wants roughly 600–1,200 µmol/m²/s at the canopy, and compact fluorescents spread a modest amount of light in all directions, so it falls off fast with distance. Research shows cannabis yield rises in step with light, so a weak light means proportionally fewer grams per square metre.

Are household bulbs fine for seedlings and clones?

Yes, household LED or fluorescent bulbs are fine for cannabis seedlings and clones, which need only about 150–300 µmol/m²/s for seedlings and 50–150 µmol/m²/s for unrooted cuttings. Use daylight-white bulbs, keep them close but not touching, and run 18 hours a day. Move plants to a proper grow light once they have three or four sets of true leaves.

What is the cheapest light that actually works for one plant?

The cheapest light that properly flowers one cannabis plant is a small dimmable horticultural LED of about 100–150 W from a fixture rated around 2.5 µmol/J or better, sized for a 60 × 60 cm (2 × 2 ft) space. It delivers roughly 600–900 µmol/m²/s over that area, which a cluster of household bulbs cannot, and costs less to run per gram.

Sources

Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. doi.org/10.3389/fpls.2021.646020

Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. doi.org/10.1038/s41438-020-0283-7

Michigan State University. Lighting of cuttings (rooting-phase PPFD). canr.msu.edu/uploads/resources/pdfs/lighting-of-cuttings.pdf