# Hypothesis: Lumens and Watts can be a good indicator of PAR(LEDs)



## poppingflatbread (Jun 28, 2017)

Hi everyone, I'm new to the hobby of planted tanks and I've been doing some google-fu research on aquarium lights. Based on the info read, I've got a hypothesis that by using the values of lumens and watts could be a good indicator of light value similar to how we use PAR as the main choice when purchasing LED lights.


Watts is not a good indicator for light the plants need, since plants accept high PAR value which is based on the light spectrum. Watts is an indicator on how strong/intensity? the light will be. Some articles/videos also indicate that red and blue leds in particular uses less Watts then say, a all white led system. [1]

Lumens are no longer a good indicator since lumen values are based on the colour spectrum in which we(humans) see. As such PAR is now favoured since this value is based on the spectrum the "plants see". But do note that it isn't so great to choose solely red and blue light, there are some experiments which indicate you still do need a full spectrum of light for a healthy plant.[2] While PAR represents the intensity of light spectrum the plants "see"

LED lights come in a wide variety of colour temperature and each colour temperature exhibits a certain pattern with regards to the spectrum.










Now here is my hypothesis, given that we have the following information:

LED colour temperatures indicate spectrum pattern usage
Watts indicate how powerful/intense? the light is (actually you could ignore this and use lumens value)
lumens represent the intensity of which we see yellow/green
 PAR value of other products which also contains temperature color/watts/lumens

Couldn't we find a good plant light by taking account of watts, lumen and color temperature? For instance when comparing a 100 watt led light with 2700k temperature vs. a 50 watt led light with 5000k color temperature(lower lumens due to less yellow/green intensity and wattage). The 50 watt would perform better since based on the spectrum usage it has more blue intensity compare to red. I'd love to hear your thoughts.











[1] https://www.youtube.com/watch?v=WPAy79_Kh-o&feature=youtu.be
[2] https://youtu.be/HawgP5SXPko?t=400


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## jeffkrol (Jun 5, 2013)

> Couldn't we find a good plant light by taking account of watts, lumen and color temperature?


sure and its already been worked out, partially.
Problem is:
1)K temp needs to be accurately known (its normally not since diodes can vary greatly)
2)L/Watt needs to known which varies w/ current/diode type and bin

Personally, since we aren't growing "crops" the tone you like is a bit more important than PAR..
Pick a K value and a CRI value that suits you and get the strongest light.. 
Cheap Lux meter will get you a Par "estimate"

See chart:
Photosynthetic Photon Flux Density (PPFD) Concepts

2700K white light LED (Philips Luxeon Rebel LXW9-PW27)...18.1

3000K white light LED (Philips Luxeon Rebel LXW9-PW30)...17.1

3500K white light LED (Philips Luxeon Rebel LXW7-PW35)...14.6

4000K white light LED (Philips Luxeon Rebel LXW8-PW40)...14.3

5000K white light LED (Philips Luxeon Rebel LXW8-PW50)...14.6

NOTE:


> for converting illuminance in kilolux to PPFD in μmol/s-m2:


http://www.egc.com/useful_info_lighting.php

LUX/67 approx PAR for a "normal" K range ..but as has been pointed out.. Don't use a phone app..
Useable eek bay lux meters are 10-40..

Granted you need the light in hand..

Point is there is no good way of taking manuf. data and getting more than a large ballpark figure


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## ChrisX (May 28, 2017)

Is this one of those things that people over-intellectualize?

IOW, has anyone ever seen a visibly bright and appealing tank light that doesn't grow plants well?

I know that enough light is very important, but many of the pro planted tanks are using predominantly high-K lighting. When people pull in red/green/lime/UV/whatever in order to increase plant growth, are they not overlooking the fact that if they just increase the appealing light, they will be getting more PAR. Which comes back to my original question: Has anyone ever seen a visibly bright and appealing tank light that doesn't grow plants well?

There might be a case where someone is using a super high-K light that is significantly missing (say) red wavelengths. Also a very warm and yellowish light might be missing blue. But neither of these are considered visibly appealing.

This is not a grow-op where efficiency/yield are important.

That being said, does obsessing over PAR readings help beyond allowing different people to compare experiences online? If a person "knows" (has 1st hand experience) what good light looks like, he can easily duplicate that with other lights.


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## clownplanted (Mar 3, 2017)

IMO your way overthinking this. Turn on some light and grow some plants 


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