Using COB LEDs as Grow Lights

While there still are reasonable applications to using HID bulbs, the advantages of using COB LED grow lights outweigh the disadvantages.

But the question remails…

Does this technology justify the cost?

The introductory price of using COB LEDs in an indoor garden is initially higher, but they pay themselves off in the long term due to several advantages.

I’m going to take the liberty and compare COB LED’s to the most commonly used high quality lighting of today, namely: HPS, CMH, & MH lights.

To make things easier here’s a nifty little chart for you:

Light Type	μmol/j (ppf/w)	Lifespan	CCT (Kelvin)	Color Rendering Index
COB LED	1.8-2.5	30,000 – 60,000	2700-6500	70-97
Double-ended HPS	1.4-1.8	10,000 – 15,000	2100-3200	20-65
Ceramic Metal Halide	1.1-1.5	15,000 – 20,000	3100-4200	80-96
High Pressure Sodium	0.8-1.7	9,000 – 17,000	2100-3200	20-65
Metal Halide	0.6-1.2	8,000 – 15,000	3200-6000	80-92
T5 Fluorescent	0.6-1.1	8,000 – 10,000	3000-6500	85

Now here’s a breakdown that helps explain the chart:

Improved Electrical Efficiency

For grow lights, efficiency is measured in μmol/j or, more simply, the amount of photosynthetically active photons that are produced per watt consumed at the wall. This can also be interpreted as μmol per watt.

Improved Lifespan

High quality LEDs have hands down the highest usable lifespan of any grow light technology available. Even if the initial investment is higher, a quality LED fixture will last AT LEAST 30,000 hours. So it’ll pay itself off over time.

Based on manufacturer literature, double-ended HPS lamps have a life expectancy of 10,000 hours to 90% survival, or 1.65 years when used an average of 16 hours per day or 6,000 hours per year (traditional mogul-base lamps have industry-reported life expectancies of 10,000 to 17,000 hours, to 90% survival, and cost about $40).

The cost of a 1000W, double-ended replacement lamp is about $140, which averages to $28 per year if we assume a lamp will be replaced once in the first five years. Lamp replacement cost increases to $30 to $35 per year when the labor to replace the bulb is included, but this is small compared to the approximately $600 per year annual electric cost to operate the fixture. Adding the cost of lamp replacement increases the five-year cost of operation by about 5%.

By comparison when operated at favorable temperatures, individual LEDs generally have a predicted lifetime (to 70% of the initial light output) of 50,000 hours, about 8.35 years when used an average 16 hours per day or 6000 hours per Year.

Improved Spectrum

This is an example of the spectrum you’ll find in most high quality COB LEDs. Please note that although there are always variations between different companies, it’s mostly the same. A 3500K 90CRI COB from any manufacturer should function very closely to any other 3500K 90CRI COB of the same voltage class.

If you’ve read about spectrums before, you’ll notice that no other single-point light source offers such a broad and targeted PAR spectrum.

Here’s the spectral reading of a few 3100k CMH Bulbs for comparison.

Improved Light Quality

One of the main reasons that COB LED grow lights have made their way so quickly into many grow rooms is because of their HIGH Color Rendering Index (usually over 80) and broad spectrum.

CRI stands for Color Rendering Index, and describes how the color of a light source changes how an object appears to the human eyes and how well subtle variations in color shades are revealed. The higher the CRI, the more realistic things look.

Regardless of the COB manufacturer, whether CREE, Citizen, Bridgelux, etc. They all offer at least 70 CRI Broad Spectrum chips and which usually can go to up to 97 CRI.

This means no purple, or extreme orange, or red or yellow but high quality white light showing realistic colors.

Allows replacement of HID bulbs without any loss of light intensity

Up until now LEDs were a choice for those who needed low power. But not anymore. As of right now LEDs are significantly more efficient at producing photons than any HID technology. Meaning that at the same power consumption, high quality COB LEDs will outperform HID technology at providing quality light for your canopy.

Better Light Distribution

HIDs and COB’s are both single-point light sources. But since COBs are comparatively easy to handle and position, we have a very different situation.

Instead of using one single light source, COB LEDs can be spaced for better uniformity in order to avoid hotspots or low intensity areas in the grow room.

A practical example would be that instead of having one big 600W HID fixture that would create a hotspot, we could have 6 COB LEDs producing the same amount of light, while consuming less and providing a way better spread.

Superior Thermal Performance

This is a tricky one, but bear with me. A 500 watt fixture will produce 500 watts of heat, period. Regardless of whether it is an HID, a CFL, or an LED. There’s a common misunderstanding that 500 watts of LEDs is cooler than 500 watts of HID, and while that is usually true, it’s not for the reasons people think.

The reason is mostly Infrared radiation. Far infrared is radiant heat, it’s the same as the feeling of warmth from the sun on your face and the heat from a coal fire. It is even the same form of heat emitted by your own body. And LEDS (unless specifically designed to do so) produce very little infrared light, now compare that spectrum to an HPS and you’ll soon understand why HPS lamps are always so hot.

COB LEDs Compared to Other Types of Grow Lights

Here’s a chart comparing COB LEDs to other types of grow lights. I ranked each light on each quality from 1-5, then added the points up to determine which lights are best.

Here’s a simple breakdown to explain the chart:

COB LEDS vs. HPS

Points for COB LEDs: 22

Where do COB LEDs beat HPS?

• Power Consumption
• Spectrum
• Efficiency
• Lifespan

Points for HPS: 12

Where do HPS beat COB LEDs?

• Initial Price

COB LEDS vs. MH

Points for COB LEDs: 22

Where does COB LEDs beat MH?

• Power Consumption
• Spectrum
• Efficiency
• Lifespan

Points for MH: 12

Where does MH beat COB LEDs?

• Initial Price

COB LEDS vs. CMH

Points for COB LEDs: 22

Where does COB LEDs beat CMH?

• Power Consumption
• Spectrum
• Efficiency
• Lifespan

Points for CMH: 14

Where does CMH beat COB LEDs?

• Easier to Source (more market penetration)

COB LEDS vs. CFL

Points for COB LEDs: 22

Where does COB LEDs beat CFL?

• Power Consumption
• Spectrum
• Efficiency
• Lifespan

Points for CFL: 11

Where does HPS beat COB LEDs?

• Initial Price
• Simple solution for low lighting situations