Spectrometers for LED Grow Lights

Why do I want a Spectrometer?

After looking at hundreds of spectrum graphs from the actual LED chip manufacturers, and dozens more from LED grow light companies claiming to use these chips, something didn't look right. It became apparent that a lot of grow light companies were posting spectrum graphs for their lights that just weren't possible.

LED diodes naturally give off slightly different colors of light on either side of their "peak" wavelength, in what is called a "normal" distribution. LEDs coated with phosphors ("white" LEDs) still have this natural "rounded" spectrum but with multiple "humps"- one for the underlying LED's, and one for the phosphors'. When LED grow light companies post spectrums with "sharp corners" in them, it seems very fishy- there is almost no way to make a spectrum look like that with LEDs. (Other methods of creating light such as discharge tubes [HID lights] can have "sharp" spectrums– just not LEDs.)

Adding to that, many LED grow light companies claim to incorporate UV diodes in their spectrum, but the spectrum graphs they show on their websites don't actually show that.

So I'm pretty sure that a lot of the LED grow light companies are lying about their spectrum, but I can't prove it- unless I get my own spectrometer.

Spectrometer Selection

Spectrometers that are reasonably accurate and can measure light outside of the visual spectrum are expensive, usually over $2,000 each. Much like LED grow lights that actually work. Like LED grow lights, each one is slightly different and has its own plusses and minuses, requiring a lot of research to find the right one.

I've identified 3 spectrometers that can do what I want at a "reasonable" price:

CompanyModelRange (nanometers)Resolution (smaller is better)Sensor overloadCan use apertureCost
AsensetekLighting Passport380-7806nmWarningNo$1,995
StellarNetBLUE-Wave UVN250-11001nm – 6nm (depending on options)DetectableYes$3,000
UPRTekMK350S380-78012nmNo noticeNo$3,095

I'd really like to have a spectrometer that covers the UVA and UVB range; the Asensetek and UPRTek spectrometers cover only the extreme upper-end of UVA, while the StellarNet covers all of UVA, UVB and some UVC.

One of the trickiest things with taking the spectrum of LED grow lights is that the grow lights are very bright lights, and spectrometers in general are designed to measure dim sources, meaning their sensors can easily get overloaded (giving incorrect spectrum readings).

The Asensetek spectrometers warn you when their sensor is overloaded and giving false readings. StellarNet doesn't provide an explicit warning, but the software doesn't automatically scale the results, so you can see if the sensor is being overloaded. Even better, unlike the Asensetek or UPRTek spectrometers, the StellarNet BLUE-Wave is designed to work with an aperture to allow you to reduce the amount of light hitting the sensor, eliminating overloading with bright light sources.

UPRTek's spectrometers don't warn you when the sensor is overloaded, and since the software automatically scales the results to 100%, you can't tell if the sensor was overloaded. When aimed at a very bright light source, it just gives you a false reading for the spectrum, and there's no way you can tell it is wrong.

Every LED grow light company with what I think is a false spectrum graph on their website has a picture or video of them using a UPRTek spectrometer. Ironically, the spectrometer that costs the most seems to be the worst choice across the board- and most LED grow light companies seem to have bought one without doing their research, or even understanding how they work. This seems a bit odd for companies claiming to be lighting and spectrum experts!

The StellarNet BLUE-Wave is a bit more expensive than the Asensetek Lighting Passport, but the additional capabilities it offers justify the cost– it is the spectrometer I want to get!

2 thoughts on “Spectrometers for LED Grow Lights”

  1. If cob lights aren’t lasting it’s not because there’s something wrong with cobs. Cobs are just diode arrays and the diodes themselves are driven at very low currents. They are the future of LED.

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