Walk into any garden center or scroll through Amazon and you will find hundreds of LED grow lights, each claiming to be the best, most powerful, full-spectrum solution for indoor growing. The listings are packed with jargon — PAR values, PPFD ratings, spectral charts — designed more to impress than to inform. I have tested a lot of these lights over the years at Wholly Water Farms, and the honest truth is that most people, especially those growing microgreens or simple herbs, are dramatically overthinking this.

Let me walk you through the terms that actually matter, what your plants genuinely need, and how to avoid spending $200 on a light when a $20 shop light would do the job perfectly well.

What Is PAR and Why Does It Matter for Grow Lights?

PAR stands for photosynthetically active radiation, and it refers to the wavelengths of light between 400 and 700 nanometers that plants can actually use for photosynthesis. This is the visible light spectrum, roughly from violet through red. When a grow light advertises itself as "full spectrum," it means the light emits energy across this entire PAR range, mimicking natural sunlight. PAR is not a measurement you will see on a spec sheet — it is the category of light we are measuring. Think of it as the playing field, not the score.

What Do PPFD and DLI Mean in Practical Terms?

PPFD stands for photosynthetic photon flux density, measured in micromoles per square meter per second (written as umol/m2/s). It tells you how many usable light photons are hitting a specific spot on your growing surface at any given moment. Higher PPFD means more light reaching your plants. A sunny day outdoors delivers roughly 1,500 to 2,000 umol/m2/s at noon. Most indoor crops need far less than that.

DLI is daily light integral — essentially PPFD multiplied by time. It measures the total amount of usable light your plants receive over an entire day, expressed in moles per square meter per day (mol/m2/d). A microgreen tray getting 200 umol/m2/s for 16 hours receives a DLI of about 11.5 mol/m2/d, which is right in the productive range. DLI is the metric that matters most because it accounts for both light intensity and duration. A dimmer light running longer hours can deliver the same DLI as a brighter light running fewer hours.

How Much Light Do Microgreens Actually Need?

Microgreens need a PPFD of roughly 150 to 400 umol/m2/s delivered over 12 to 16 hours per day, which translates to a DLI of approximately 9 to 16 mol/m2/d. Most commercial microgreens operations standardize around 180 to 200 umol/m2/s, which produces excellent color, compact growth, and good nutritional density without excessive energy cost. This is a modest amount of light by indoor growing standards. For comparison, flowering plants like tomatoes and peppers want 400 to 800 umol/m2/s or more.

The practical implication is significant: microgreens do not need expensive, high-output grow lights. A basic 4-foot LED shop light pulling 40 watts delivers enough light for a shelf of four standard 10x20 trays when mounted 6 to 12 inches above the canopy. I have run side-by-side comparisons at our farm between $20 shop lights and $150 purpose-built grow lights, and the microgreens grown under the shop lights were indistinguishable in quality, yield, and appearance.

Should You Buy Full Spectrum or Red/Blue Grow Lights?

The older generation of LED grow lights used only red and blue diodes, creating that distinctive purple glow. Plants primarily use red and blue wavelengths for photosynthesis, so the logic was sound. But research over the past decade has shown that the green wavelengths in between — the ones that make full-spectrum lights appear white — also contribute to photosynthesis and play important roles in plant morphology and nutritional content. Full-spectrum lights produce better-looking microgreens with more natural coloring and, according to several studies, higher concentrations of beneficial phytochemicals.

The other practical advantage of full-spectrum white lights is that you can actually see what your plants look like. Under purple blurple lights, it is nearly impossible to spot discoloration, mold, or nutrient deficiency. White light lets you monitor crop health accurately. At this point, there is no reason to buy red/blue only panels for microgreens or herbs.

Are Cheap LED Shop Lights Good Enough for Growing?

For microgreens, yes. A 4-foot LED shop light in the $15 to $25 range from any hardware store will deliver 150 to 250 umol/m2/s at 6 to 8 inches from the canopy, which is plenty for sunflower, radish, pea shoot, and most brassica microgreens. These lights typically draw 32 to 44 watts and cover a 4-foot by 1-foot area effectively. For a standard wire shelving rack with four shelves of microgreens trays, you are looking at four shop lights costing $60 to $100 total.

For lettuce, herbs, and other crops you intend to grow to full size, invest a bit more. Purpose-built grow lights in the $50 to $100 range offer better spectral tuning, higher PPFD output, and more even coverage across the growing area. Brands matter less than the actual specs — look for lights that publish independent PPFD maps showing intensity at different distances and positions.

How Much Does It Cost to Run Grow Lights?

Electricity cost is straightforward to calculate. Take your light's wattage, multiply by hours per day, divide by 1,000 to get kilowatt-hours, then multiply by your electric rate. A 40-watt shop light running 16 hours per day uses 0.64 kWh per day. At the Florida average of roughly $0.13 per kWh, that is about $0.08 per day, or $2.50 per month per light. For a four-shelf rack with four lights, you are looking at roughly $10 per month in electricity for lighting.

A 4-foot LED bar covering a shelf of four microgreens trays and running 16 hours a day for a 10-day growing cycle costs approximately $0.80 to $1.00 for that cycle — about $0.20 to $0.25 per tray. When your trays sell for $15 to $25, electricity is a rounding error in your cost structure. Even if you tripled your light intensity by moving to higher-output fixtures, the electricity cost per tray stays under a dollar.

How Do You Measure Light Reaching Your Plants?

Ideally, you would use a dedicated quantum PAR meter, which runs $100 to $500 depending on accuracy and features. For a commercial operation, this is a worthwhile investment. For a hobby grower or someone just starting out, several smartphone apps can give you a rough approximation — not lab-accurate, but close enough to confirm your lights are in the right ballpark. The Photone app is one of the better options available.

More useful than precise measurement is understanding the relationship between distance and intensity. Light follows the inverse square law: double the distance and you get roughly one-quarter the intensity. This means the difference between mounting your shop light 6 inches above the tray versus 12 inches is substantial. For microgreens, I keep lights 4 to 8 inches above the canopy and raise them as the greens grow.

The Diminishing Returns of Expensive Lights

There is a real point of diminishing returns with grow lights, and it is lower than most people expect. For microgreens, which grow for 7 to 14 days and never develop beyond their first true leaves, the difference between a $20 shop light and a $200 horticultural fixture is essentially zero in terms of harvest quality and yield. The expensive light might save a few watts in electricity, offer slightly more even coverage, or last longer — but the return on investment is measured in years, not months.

Where premium lights make sense is in production of fruiting crops, full-sized lettuce heads, and other long-cycle plants where light quality and intensity directly impact yield and revenue. For those growers, investing $100 to $200 per light is justified. But if you are growing microgreens, sprouts, or simple herbs, start with the cheap stuff. You can always upgrade later once you know exactly what you need.

Frequently Asked Questions

How many hours per day should grow lights run for microgreens?

Run grow lights 12 to 16 hours per day for microgreens. Most growers settle on 14 to 16 hours, which provides a DLI in the optimal range of 9 to 16 mol/m2/d at moderate PPFD levels. Use a simple outlet timer to automate the schedule. Consistency matters more than precision — pick a schedule and stick with it.

Can regular LED bulbs grow plants?

Regular LED bulbs emit some PAR light and can sustain low-light houseplants, but they are not efficient for growing food crops. Their light output is diffuse and weak compared to tube-style shop lights or purpose-built grow fixtures. A single LED bulb might keep a basil plant alive on a windowsill, but it will not produce vigorous growth or good microgreens yields.

Do grow lights use a lot of electricity?

LED grow lights are remarkably energy-efficient. A typical 40-watt shop light adequate for one shelf of microgreens costs about $2.50 per month to run at average Florida electricity rates. Even a full four-shelf growing rack with four lights runs approximately $10 per month. Compared to older fluorescent or HID lighting, modern LEDs use 40 to 60 percent less electricity for the same light output.

What does "full spectrum" mean on a grow light?

Full spectrum means the light emits wavelengths across the entire PAR range from 400 to 700 nanometers, appearing white to the human eye. This mimics natural sunlight and provides all the wavelengths plants use for photosynthesis and development. Full-spectrum lights produce healthier, more natural-looking plants compared to red/blue only fixtures and allow you to visually inspect crops for problems.

How far should LED grow lights be from microgreens?

Mount LED grow lights 4 to 8 inches above the microgreens canopy for optimal light intensity. At this distance, most shop lights deliver 150 to 300 umol/m2/s of PPFD, which is ideal for compact, colorful growth. Raise the lights as the greens grow to maintain consistent distance. Too close can cause heat stress; too far reduces light intensity significantly due to the inverse square law.