How to measure the action spectrum of light?

[keith1975]

If you look at a light being sold on Amazon, you often see graphs like this:

This image seems to show the "Action Spectrum". But I could not find more info on this except what is shown here: Action spectrum - Wikipedia

"An action spectrum is a graph of the rate of a physiological activity plotted against wavelength of light. It shows which wavelength of light is most effectively used in a specific chemical reaction. Some reactants are able to use specific wavelengths of light more effectively to complete their reactions."

I want to be able to generate these graphs. It's the only way I can test lights myself and make sure they are the quality that I need.

Does anyone know how to generate these graphs? What device do I need? I have a lumen meter, but I think for this you need chemicals and papers and stuff. But I'm not a chemist, so I'm not sure!

Any help would be greatly appreciated!

 

[Stunned]

best advice is to ignore graphs from people like Beastva
lumen or lux meter is useless when measuring for LEDs
You want to see measurements in PAR or PPFD
Honestly these days when it comes to lights you have 2 choices for best solutions
COBs or Quantum boards, they are both great
everything else including blackdogs, kind, cali lightworks ect, ect, ect is sub par

 

[keith1975]

Thanks! That is useful. But due to me testing 3 different brands, I really would like to do it scientifically so I have values to compare. Do you know what type of device is needed to measure PAR and PPDF? And maybe where to get such a device?

And I would still like to know how to get those spectrum graphs. It's information that will be massively useful when comparing different lights.

 

[Stunned]

if you have to ask me these basic questions, then I suggest you have no business testing in the first place

 

[keith1975]

The PAR and PPDF I can figure out myself. Will do some searching. Sorry for asking.

But for the spectrum question, I have done some searching and can't find a clear answer as to how to do a test to get that graph. Would be great if someone could point me in the right direction?

 

[Stunned]

google LED Gardener
sorry for being so harsh

 

[keith1975]

Very cool link with loads of existing tests. Thanks! Will keep going down the rabbit hole and report back if I find anything worth mentioning.

 

[Ennui]

Each manufacturer should have a spectrum graph in their literature. They use a prism to separate and determine make-up of the spectrum from a source, I'm thinking. PAR is the concentration of Photosynthetic Activating Radiation over a given area. Prism would tell the temperature of the water and PAR the force of the spray if you compare it all to a shower. I'm aware I said Activating when everything else says Active, but it just ain't good English, don't make no sense.

 

[keith1975]

manufacturers lie. Which is why I'd prefer to be able to do the test myself. And was hoping there's either some sort of device that you can use to do it, or clear instructions somewhere if it's more intricate than just using a device.

 

[Stunned]

{laughs}
The work has already been done bud
You can go to Samsung's website to see the tests they've done on their diodes
Are you vetting or disputing what millions of dollars of research has already been published
I'm thing you're just trolling or being a drama queen
Manufacturer's may well lie, but we are well beyond that now with Samsung, Cree, Vero and Citizen
coffee?

 

[keith1975]

I trust Samsung. It's Mars Hydro and some of the other brands I dont trust.

Look, I've bought a bunch of different lights and would like to see how the stack up. Also want to see how different configurations will stack up and how that will change the result. If I am being a drama queen for wanting to do that, then my bad I guess. My question was how they generate those graphs. Which I think is a valid question. If you don't know, then you can just say, "i dont know", or nothing at all for that matter. But if you do know how to do it, please do reply so guys like me can look at doing it ourselves (if it's even feasible).

 

[Stunned]

Have you seen the graphs for light PPFD on Mars, Bestva, ect?
What more do you need to see?
Here's a thought...
Read the specification reports for the LED diode manufacturer's, and surmise a logical prediction
I'm not holding my breathe on that
There is no mystery, other than spin bullshit to confuse new customers
It's Cree, Vero, Citizen COB's or Quantum boards
And it has to be passively cooled, so active fans is a fail in design
No testing needed
All these lights at this time work very well

 

[TurboBucket]

Spectral radiometer

 

[Nick420Guy]

I have seen videos on youtube where they have an app on their phone. Not too sure how accurate it is tho.

 

[Ennui]

Spectral radiometer

That's the word I was looking for last night, Spectrometer! :forehead slap:

 

[Ennui]

The PAR and PPDF I can figure out myself. Will do some searching. Sorry for asking.

But for the spectrum question, I have done some searching and can't find a clear answer as to how to do a test to get that graph. Would be great if someone could point me in the right direction?

Unless you have a PAR meter, that's the number I'd be more concerned with. If you insist on any easy home test for spectrum, open the chamber just enough to let a crack of light through. Put a prism in front of the crack and focus it on a piece of white paper. The width and sharpness in the bands should correlate with the graphs. You'll only see the visible range, though.

If you're having a problem and think this is the root cause I'm thinking you're doing something else wrong. You can get something decent out of just about anything if used correctly.

And you have to think, you mentioned some popular names. Why would they open themselves up to liability by smudging a spectrum chart? I'm sure there are the exception, as with anything, but I don't see the village up in arms about this.

Hope you find the info you're after.

 

[Mars Hydro]

Usually manufacuturers will use the machine below to test the lumen, spectrum, draw power, etc. And this is very acurate since it put the light inside the ball, no light will coming out, it will test the full lights output.
I believe there is some spectrum test tools in the market as well, for personal use, it is more convinient, seen them from the youtube videos, but not sure about the brand.

 

[PurpleGunRack]

There's no need to test this yourself unless you're developing lights or like to bulk purchase shifty diodes from alibaba.

Just look at the data sheets

LM301b.png

• PurpleGunRack
• Oct 10, 2018

If you want to measure the light output within the PAR range, you need a Quantum Sensor, the cheapest accurate sensor available is from Apogee.
However, this purchase only makes sense for big operations or light geeks, the money would be way better spend on better light, climate control, genetics etc.

 

[LEDXpert]

Par is a measurement of photo active radiation. Meaning everything plant can use. Those action spectrums are for chlorophyll production which is why blurple lights were first LED. Full spectrum is now considered better for full plant development and white light has gotten efficient enough to be good.

I disagree with only quantum boards or cobs. Other brands listed will work fine. Quantums and cobs are just raw LEDs so you dont have light losses from lenses. This can work for home use but you have to be careful of shock hazards. COBs and good because they are cobs they are just cost effective and have gained acceptance. They are just one big LED. Both are just regular white LEDs.

 

[Stunned]

why do you have to be careful of shock hazards as opposed to anything else you plug into a wall outlet?