Grow Lighting FAQ

Crop Growth Lighting Fundamentals Explained

UPDATED: 08-11-2025

Grow lighting can be one of the more mystifying aspects of starting and running an indoor garden, urban farm, or greenhouse with supplemental crop lighting. To help clear things up, we’ve put together this Grow Lighting FAQ.

There are many choices for grow lights—and plenty of hype—whether from a local hydroponics store or an online vendor. This guide is designed to help sort fact from fiction so that both new and experienced growers can better understand the principles behind the crop lighting they choose, and get the best return on investment from their gardening efforts.

What often adds to the confusion is that different lighting technologies can all deliver good results for plant growth, fruiting, and flowering—but they’re not all the same. It’s a case of apples versus oranges.

So, let’s get started with our Grow Lighting FAQ.

Grow Lighting FAQ #1: Different Types of Grow Lights

What are the most important differences between HPS (high pressure sodium), MH (metal halide), CMH/LEC (ceramic metal halide/light emitting ceramic), fluorescent, and LED (light emitting diode) crop lighting?

LED

LED grow lighting can be astoundingly efficient—or a waste of money—depending on the specific system you choose. Results vary because LEDs are not as standardized as HPS, MH, CMH/LEC, or fluorescent technologies. Differences in performance depend on factors like the drivers, diodes, reflectors, and the blend of LED chips in the fixture.

LEDs have become the standard for most indoor and greenhouse growers thanks to rapid evolution and increasingly competitive prices. They’re available in a wide range of wattages and coverage areas, with excellent control over dimming and even spectral output (including UV). Dynamic LED systems go a step further, using sensors and computers to make real-time adjustments, such as when supplementing natural light.

Advantages:

Highly efficient; excellent yields per watt
No lamp replacements required
Tuneable spectrum and intensity
Lower fixture temperatures
Compatible with dynamic crop lighting systems
Good potential for power savings
Can be mounted close to plant canopies in multi-tier setups

Disadvantages:

Higher initial cost
Results vary greatly between manufacturers
Some fixtures have a large physical footprint

dynamic led grow lights changing spectrum output

Above: The same LED grow lighting system producing different spectral outputs

HPS

Tried, tested, and true, HPS systems are relatively inexpensive for the amount of light they produce. However, they’re less energy-efficient than some alternatives—the sheer light output compensates for lower spectral quality, but at the cost of higher power bills. They’re most often available as DE (double-ended) lamps for higher efficiency and lifespan, with single-ended lamps common in lower wattages.

Tip: The high percentage of red and orange in the HPS spectrum makes it best for flowering and fruiting plants.

Advantages:

Low purchase cost
Capable of big yields per light
Good canopy penetration and coverage
Small physical footprint

Disadvantages:

High power consumption
Produces significant heat
Lamps need replacement every 12–18 months
Poor spectrum, limited tunability
Requires greater vertical clearance from canopy

Above: Installing Aerospace Grade DE HPS Lighting Systems in a Commercial Grow Facility

MH

Metal halide systems share many pros and cons with HPS, but tend to produce higher-quality light with slightly less intensity per watt. They’re often preferred for leafy greens and herbs because their higher blue spectrum encourages strong vegetative growth.

It’s now rare to see MH used in commercial crop cultivation.

CMH/LEC

Still a type of HID lighting, CMH/LEC consumes less power for the amount of yield produced compared to other HIDs. They’re becoming less common overall, but still popular for vegetative growth, such as maintaining mother plants and raising transplants.

Their pros and cons are similar to HPS/MH, though they run slightly more efficiently.

Above: (left) 315 watt CMH, (right) 320 watt dual element CMH grow light

Fluorescent

T8 and T12 fluorescent tubes were once popular for propagation from seeds or cuttings, before transplanting into stronger light. Today, fluorescent strips have largely been replaced by LED strips for this purpose.

Above: Fluorescent Lights are ideal for plant propagation or smaller light loving plants

Above: LED strip grow lights are a common replacement to fluorescent lighting strips for cultivation.

Grow Lighting FAQ #2: Is a Brighter Light with More Intensity Going to Produce Better Results?

Not always. While higher intensity can improve yields in light-loving plants, spectrum matters greatly. A more intense light with the wrong spectrum may not deliver better results and can even stress, burn, or bleach plants if misapplied.

Grow Lighting FAQ #3: What’s the Difference Between Tuneable and Dynamic LED Grow Lights?

Both allow adjustments to intensity and/or spectrum. The key difference is that Dynamic systems can adjust in real time—on a schedule or in response to changing conditions—making them adaptive. This is ideal for consistent greenhouse crops and can save significant energy. Tuneable LEDs are more of a “set it and forget it” option, with limited adjustment ranges.

Grow Lighting FAQ #4: Grow Light Safety

Always choose lights rated for the application—CSA or UL approval is essential. For greenhouse use, they should also be suitable for damp environments.

Like any appliance, grow lights are safe when used as directed and with common sense. Used carelessly, they can cause accidents or injury.

Tips:

Never overload circuits
Keep cords away from wet areas
Securely hang lamps at safe distances
Always wear eye protection when lights are on
Have any extra wiring done by a qualified professional

Grow Lighting FAQ #5: How Much Light Do Plants Need?

Most plants have a direct relationship between light energy received and final yield/quality, though shade plants prefer lower levels. Vegetables, greens, flowers, fruits, and herbs generally thrive with higher light levels.

A light meter can help fine-tune lighting, but should be used as a reference, not an absolute. For example, a meter may show that an LED flashlight is brighter than midday sun—but that doesn’t mean it’s useful for photosynthesis.

For high-light plants, aim for 800–1000 μmols for flowering/fruiting, or 5000–7500 lux. Efficiency matters over the long term, so consider electricity costs and lamp replacement frequency when buying a fixture.

For commercial growers, the best approach is to use light sensors to deliver a target Daily Light Integral (DLI)—the total amount of PAR light received over 24 hours. This ensures optimal growth without wasting power and is a hallmark of dynamic lighting systems.

DLI reporting and control console for grow lighting systems

Above: This grow lighting system uses DLI to manage crop lighting based on sensor readings and pre-set DLI targets.

Grow Lighting SAQ (Should Ask Question): What About Green Light?

True green light won’t interrupt a plant’s dark cycle, making it useful for night work in grow rooms or blackout greenhouses. However, coated incandescent or fluorescent bulbs are not true green and will emit red/far-red wavelengths that disrupt the dark period. True green LEDs are best for night work.

Super Pro Tip: Green light increases insect activity. Running green lights for several hours before applying pest control can make treatments more effective.

Update: New studies suggest that green wavelengths can also influence plant development—it’s not just for nighttime checks anymore.