Reasons to Choose Screw-in Grow Light Bulbs
Screw-in bulbs can be a great way to add grow lights to your indoor garden. If you’re looking for a small indoor grow light they’re ideal — affordable and easy to setup.
You don’t need anything special to install your grow light. A clamp light fixture or a plug-in pendant fitting are the simplest options. Both can be adjusted easily to get the right plant-to-light distance.
Hands-on Testing = Real Results
At Bright Grow Co. we only review products we’ve used and tested ourselves.
That might seem like a basic requirement — sadly not everyone does it this way. Other sites simply regurgitate press releases and Amazon reviews. Never laying eyes on the products they “review”.
At Bright Grow things are different. We only review products after extensive hands-on testing. So you can trust our recommendations.
We’re looking for screw in grow light bulbs that meet these three criteria:
- Bright — herbs and vegetables need strong light to thrive.
- Safe — must be certified for electrical safety.
- Efficient — up to modern standards for energy efficiency.
Narrowing the Field
There are lots of LED grow light bulbs that consume 10-20 Watts of electricity — they’re just not bright enough for the vegetable and herb growing. They might be fine for houseplants — which tend to be less demanding.
Some bulbs that are bright enough don’t have the safety certification we insist on. (UL or ETL — CE doesn’t cut it).
We started out the review with a field of 6 screw-in grow lights. Only two make the cut though. As it stands in 2021, we have two contenders for best screw-in grow light:
SANSI 36-Watt Daylight LED Plant Light Bulb
GE Lighting 32-Watt PAR38 LED Grow Light
How We Measure Light
Strong plant-useful light is the number one factor for picking the right grow light.
Many reviewers will use Lumens, Lux or Foot Candles to compare grow light strength. Those aren’t the right measurements for grow lights though — they’re for measuring how we humans perceive brightness.
The proper measure of plant-useful light is PPFD (Photosynthetic Photon Flux Density). PPFD is a count of the number of light photons falling on an area.
To measure PPFD you need a “quantum meter”. Quantum meters cost hundreds of dollars. So most gardeners and reviewers settle for lesser measures.
We use a state of the art Apogee Systems sq-520 quantum meter to measure PPFD for every light we test. So you get the exact answer about which lights will be best for your plants.
GE 32-Watt Grow Light
- Energy efficient LEDs — just $18/year electricity costs
(12 hours per day using the average U.S. power cost of 13¢/KWH).
- Metal built for efficient heat dissipation.
- UL certified for safety
- Available in an advanced-red version for fruits and flowers.
- Heavy bulb – twice as heavy as a typical bulb so a sturdy fixture is needed.
- Gets warm (but not hot) in operation.
Sansi 36-Watt Grow Light
- Energy efficient LEDs — $20/year electricity costs
- ETL certified for safety
- Heavy bulb – not quite as heavy as the GE bulb though.
- Gets warm, not hot in operation.
Brightness Showdown - Leafy Greens Test
Leafy greens and herbs grow well under a screw-in grow light. Many greens like similar light intensity. Lettuce, arugula, basil, cilantro, spinach… all have a “light appetite” of 12-16 DLI.
You can read about DLI if you like. All you need to know though is that DLI is the quantity of light a given plants needs.
Using our measurements of the output from the Sansi and GE bulbs we can determine exactly what planting area they can light up to keep these plants happy. We’ll assume a 12hr on/12hr off light cycle — that’s comfortable for nearly all plants.
GE 32-Watt grow bulb is the clear winner here. It provides optimal light for leafy greens over a 10-inch circle when positioned 18″ above.
The Sansi is a distant runner-up. At the Sansi’s optimal distance of 11″ it throws sufficient light over one-third area that the the GE achieves.