How can I know if light's PPFD is suitable (How far)?

Let's briefly introduce what PPFD is.

PPFD, or Photosynthetic Photon Flux Density, refers to the number of light particles (photons) that land on a square meter per second within the photosynthetically active radiation (PAR) range.

You can think of light as raindrops falling from LED chips. PPFD tells us how many of those drops fall on a specific area at a specific height each second. Since light spreads as it travels, PPFD decreases as the coverage area increases.

1. From a design perspective

Factors affecting PPFD are:

• The distribution of LED chips

• The beam angle of the light

Distribution

The main difference between board-style (PCB) and bar-style (BAR) lights lies in how the chips are arranged. Board lights concentrate LEDs in a small area, while bar lights spread them out. So even at the same power, their light uniformity is different.

It's like using a flashlight — with a fixed power, you can't get both a wide beam and high brightness at the same time.

Beam angle

Another important aspect is the beam angle. LEDs can be equipped with lenses to control how wide or narrow the light spreads — like focusing a laser pointer.

One example is SANlight GmbH (In another article, we made a brief product analysis for TOP 20 searched grow light brands in 2025. Click here to jump), 

which uses lenses to extend the coverage of its compact board-style lights. The result is a small fixture with light uniformity similar to a bar light — all thanks to the lens.

However, this design comes with risks:

Lens material is low quality → light loss → heat buildup → lens aging → more light loss.

This creates a vicious cycle. That's why it's important to pay attention to both lens quality and heat dissipation. SANlight GmbH seems aware of this and highlights both features in their marketing.

That's the general idea behind LED layout and beam angles. But product design goes deeper — and one critical issue is light overlap.

Light overlap doesn't just happen between different lights. Even within a single fixture, each LED chip emits overlapping light patterns. That's why more detail-oriented manufacturers calculate LED density rather than just spacing them evenly.

2. From a usage perspective

The main factors affecting PPFD are: Mounting height & Light placement

Raise the light, and PPFD drops. Lower it, and PPFD increases. When two lights are placed close together, the overlapping zone gets a higher PPFD.With these principles, you can adjust your setup to achieve the ideal PPFD for your plants.

3. How to read manufacturer PPFD charts:

Check the testing height 

— some charts are measured at 30cm, others at 60cm. Different heights lead to very different PPFD values.

Check the uniformity

 — a good grow light isn't just bright, it spreads light evenly.

Look at how much the numbers vary across the chart. If the center is 1200 µmol/m²/s but the edges are only 500, it’s better suited for small grow areas.

Step 1: Wattage

From the title and model, we can tell that the two products are 810W and 1080W respectively.
The 1080W model obviously has higher wattage, which theoretically means it can deliver higher light intensity (PPFD). This makes it more suitable for plants with higher light demands or densely planted environments.

Step 2: Area Covered
Both lights are tested in areas of 3ft × 3ft (about 90cm × 90cm) or 150cm × 150cm, showing they are designed for similar grow space sizes, such as a standard grow tent.

Step 3: Test Height
There are two test heights: 30cm and 60cm. When comparing, it’s important the height is the same, as height is a key factor in controlling both PPFD and light uniformity.

Step 4: PPFD Value Analysis

Using GL-QB810W as an Example

• At 30cm:
  • Center peak: 2005
  • Lowest edge: 295
  → There's a large difference in light distribution between the center and edges.

• At 60cm:
  • Center: 1445
  • Edge: 402
  → The distribution is more even, with better overall coverage.

From the analysis above, we can roughly see that the PPFD values show uneven light distribution, with more light in one direction than the other. There's also a big difference between the center and the edges, which is a strong sign that this is likely a PCB-type grow light.

Finally, consider buying a PPFD meter. It's a simple tool that lets you measure light at different positions. You'll be able to fine-tune your grow light height and spacing, making your entire lighting system more precise and efficien

Where light grows, so does knowledge. Hope everyone is inspired by sharing!