Grow lights are worth it for one application and marginal for most others. The application where they make clear economic sense is seed starting - 6-8 weeks of indoor growing in late winter, with small seedlings under modest fixtures, producing transplants worth $1-6 each at nursery prices. The application where the math falls apart is year-round vegetable production under artificial light, which typically costs more in electricity than the produce is worth.
Understanding where the line is requires knowing the actual numbers.
Light type comparison
The three practical options for home growers, along with one legacy type you might encounter:
| Type | Cost per fixture | Wattage | PPFD at 12” | Lifespan | Best use | Annual electricity at 16 hr/day |
|---|---|---|---|---|---|---|
| T5 fluorescent | $40-80 | 48-54W per 4-ft fixture | 150-300 µmol/m²/s | 20,000 hr | Seedlings and greens; adequate for herbs | $34-39 |
| T8 LED shop light | $20-40 | 22-36W | 120-250 µmol/m²/s | 50,000+ hr | Direct replacement for T5; better efficiency | $16-26 |
| Full-spectrum LED bar | $50-150 | 20-50W | 200-600 µmol/m²/s | 50,000+ hr | Seedlings through fruiting crops if mounted correctly | $15-37 |
| HPS/MH (HID) | $100-300 + ballast | 250-1000W | Very high (600-2000+) | 10,000-24,000 hr | Commercial production; generates substantial heat | $182-730 |
PPFD (Photosynthetic Photon Flux Density, µmol/m²/s) is the actual measurement of light intensity at the plant surface. For reference: seedlings need 150-250 µmol/m²/s; leafy greens 200-400; fruiting crops 400-600+. Most T8 LED shop lights and quality T5 fixtures deliver adequate PPFD for seedlings at 6-12 inch mounting height. Getting enough PPFD for fruiting crops under LED bars requires close mounting (6-8 inches) or high-wattage fixtures ($100+).
The T8 LED shop light ($25-35, 32W) has essentially replaced the T5 fluorescent as the sensible choice for seed starting and greens. Lower wattage, similar or better light output, runs cooler, lasts 2-3x longer. If you’re building a seed starting setup today, start here.
Electricity cost math
The U.S. average residential electricity rate was $0.124/kWh in 2023, ranging from $0.086/kWh in Louisiana to $0.288/kWh in Hawaii (U.S. Energy Information Administration, Electric Power Monthly, December 2023). Most of the continental US falls in the $0.10-0.18/kWh range.
Cost calculation for one T8 LED shop light (32W):
- 32W ÷ 1,000 = 0.032 kW
- 16 hours/day × 0.032 kW = 0.512 kWh/day
- 0.512 kWh × $0.13/kWh (national average) = $0.067/day
- Monthly: $0.067 × 30 = $2.01/month
- Annual (if run all year): $0.067 × 365 = $24.46/year
For seed starting, you’re not running the light all year - just during the 6-8 week pre-transplant window:
- 6 weeks × 7 days = 42 days
- 42 days × $0.067/day = $2.81 total electricity cost for the entire seed starting season
Two fixtures for a 4-tray setup: $5.62 in electricity for 6 weeks. The fixture costs $25-35 and lasts 10-15 years. Amortized over 10 years: $3-4/year in fixture depreciation.
Total annual seed starting cost: ~$6-10 in electricity + $3-4 in fixture depreciation = $9-14/year.
Seed starting ROI: the clear positive case
A 4-tray seed starting setup with two T8 LED fixtures produces:
- 2 trays tomatoes: 64 cells × 80% germination = 51 transplants × $3 nursery price = $153
- 1 tray peppers: 32 cells × 75% germination = 24 transplants × $4 nursery price = $96
- 1 tray herbs (basil, parsley): 32 cells × 85% germination = 27 transplants × $2 nursery price = $54
Total transplant value: approximately $303. Annual cost: $9-14.
Return on investment: $303 ÷ $14 = 22x. Even if you grow fewer trays or achieve lower germination rates, the economics are compelling. This is why a $30 LED fixture purchased for seed starting is one of the highest-ROI investments in the home garden.
The caveat: this math only holds if you would have purchased transplants at nursery prices. If you would have started seeds in a south-facing window anyway, the comparison is window vs. grow light - not grow light vs. buying transplants. In that case, the grow light’s advantage is consistency and timing control, not pure cost savings.
Year-round vegetable production: where the math fails
A 4x2 foot LED panel system for year-round greens might cost $80-150 in fixtures and run at 80-120W. Let’s model a modest setup: two 40W bars covering about 2 sq ft of growing area, running 16 hours/day year-round for lettuce production.
Electricity cost:
- 80W total ÷ 1,000 = 0.080 kW
- 16 hours × 0.080 kW = 1.28 kWh/day
- 1.28 kWh × $0.13/kWh = $0.166/day
- Monthly: $5.00
- Annual: $60.61
Fixture cost amortized over 5 years: $120 ÷ 5 = $24/year
Total annual cost: $60.61 + $24 = $84.61/year
Annual production from 2 sq ft under lights:
- Lettuce, 4 plantings/year (one every 3 months, 60-day grow cycle)
- 2 sq ft × 0.25 lb/sq ft per planting × 4 plantings = 2 lb/year
- At $3.50/lb for baby greens: $7 in lettuce value
$84.61 spent to produce $7 in lettuce. This is the case against grow lights for year-round vegetable production.
Where grow lights do make sense beyond seed starting
Microgreens: the exception to the year-round math. Microgreens (sunflower, pea shoots, radish, mustard) grow in 7-14 days, require only 2-3 inches of soil depth, and sell for $15-25/lb at farmers markets. Under a single T8 shop light covering one 10x20 tray, you can produce one tray every 2 weeks. At 0.2 lb per tray × $18/lb = $3.60 per tray × 26 trays/year = $93.60. Annual electricity for one light: $24. Annual net: $69.60. This is a different crop than full-size lettuce because the production density and value per ounce is dramatically higher.
High-value herbs in winter: fresh basil in January costs $4-6 per 0.5 oz package at specialty grocery. If you use it regularly, growing under lights through winter can make economic sense. Basil needs 400+ µmol/m²/s and temperatures above 65°F - this requires more powerful fixtures than basic seed-starting lights, but quality LED bars in the $50-100 range deliver adequate PPFD for herb production.
Zone 5-6 tomato seed starting timeline: in Zone 5-6, tomato transplants need to be 6-8 weeks old at transplant time (late May), meaning seed starting in late March. Without grow lights, a south-facing window in late March provides 8-10 hours of sun at low angle - adequate but variable. Grow lights provide reliable 16 hours daily and allow you to adjust timing precisely. The value isn’t just economics; it’s consistent, predictable seedling quality every year.
Light spectrum and what it actually matters for
Early LED grow lights used red-blue (blurple) spectrum because those wavelengths are most efficiently absorbed by chlorophyll. The plants grew, but the light was unpleasant to look at and made it hard to assess plant health visually. Modern full-spectrum LEDs cover the full visible wavelength range (400-700nm) with emphasis on the 400-500nm (blue) and 600-700nm (red) bands that plants use most. The white light is easier to work under and produces plants that look and behave normally.
For practical purposes, what spectrum matters for:
Blue light (400-500nm): drives compact, stocky vegetative growth. Seeds started under blue-heavy light develop thick stems and short internodes - exactly what you want for transplants. Insufficient blue light produces leggy, weak seedlings that fall over. This is why seed starting under incandescent bulbs (red-heavy, low blue) produces poor results. Standard T8 LED shop lights have adequate blue output for seedlings.
Red light (600-700nm): drives flowering and fruiting. Fruiting crops like tomatoes and peppers need red light to trigger flower initiation. A setup heavy on blue but light on red will produce robust vegetative growth but poor flowering. For seed starting, this is irrelevant - you’re not trying to flower the plants. For fruiting crop production under lights, it matters.
Full spectrum (400-700nm): the best choice for any single-fixture setup that needs to do multiple things. Full-spectrum LEDs at adequate wattage handle seedlings, greens, herbs, and fruiting crops (if mounted close enough).
The practical takeaway: standard shop LED fixtures handle seed starting and greens adequately and cost $20-40. For fruiting crops under lights, you need full-spectrum LED bars with higher wattage and closer mounting. The cost difference ($50-150 for a quality bar vs $25-40 for a shop light) is justified only if you’re actually growing fruiting crops.
Managing lights: height, duration, and common problems
Mounting height: too far and plants stretch toward the light, producing weak, leggy growth. Too close and leaves bleach or burn. The right height depends on wattage: T8 shop lights at 4-6 inches for seedlings, 6-12 inches for established greens. LED bars at 6-8 inches for most seedlings; check manufacturer PPFD specs at different distances to calibrate.
Adjust height as plants grow. A seedling tray needs lights close during germination; once plants are 4-6 inches tall, raise the lights slightly to maintain appropriate distance without the canopy touching the fixture.
Duration: 14-16 hours per day for most vegetables and herbs. Less than 12 hours produces slow, weak growth. More than 18 hours is unnecessary and the additional electricity cost doesn’t improve yield. A $15-25 mechanical timer eliminates the daily on/off management.
Leggy seedlings: the most common grow light problem. Causes: lights too high, duration too short, insufficient wattage, window supplementation that varies by day. Diagnosis: if seedlings are stretching toward the light and producing long internodes between leaf sets, the light intensity is inadequate. Move lights closer or increase duration before assuming the fixture is defective.
Tip burn on lettuce: a physiological condition (not disease) where leaf edges turn brown and die. Caused by insufficient calcium uptake at the growing tip, often exacerbated by high temperatures and rapid growth under lights. Reduce temperature slightly, ensure good airflow, and avoid overfertilizing with nitrogen. Tip burn on lettuce under grow lights is common at higher production intensities and represents a real yield and quality reduction.
The practical setup recommendation
For seed starting only: two T8 LED shop lights (32W each) on a 4-foot shop light fixture, mounted on an adjustable-height shelving unit. Total cost: $50-80. Annual electricity: $10-15 for 6-8 weeks of use. Produces enough transplants to supply a full household garden. This is the highest-ROI grow light setup available.
For seed starting plus winter herbs: add one full-spectrum LED bar (40-50W) at 6-8 inch mounting height over a small shelf or window box for herbs. Run herbs at 14-16 hours in winter. Additional annual electricity: $20-25 for 5 months of winter operation.
For year-round production beyond herbs: run the actual numbers for your specific crop, electricity rate, and production volume before committing to a substantial setup. Most crops don’t pencil out against the electricity cost unless the crop has high value per ounce (microgreens, specialty herbs) or you’re supplying a market where retail prices are meaningfully higher than grocery.
Related reading: Seeds vs. Transplants - when starting from seed is better than buying transplants, and vice versa