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Invisiblekoraks
Registered: 06/02/03
Posts: 26,667
Re: Question about Grow Light and Wattage. [Re: Kryptos]
    #28505526 - 10/15/23 01:05 PM (3 months, 11 days ago)

Quote:

Kryptos said:
So, I'm guessing your 1000w bulb that consumes 100w is giving off the light equivalent of a 1000W incandescent bulb, but only using 100W of actual power.




Yup, that's most likely it.

It's basically just misleading and confusing. And I don't think that when it comes to grow lights, a 100W LED unit is really equivalent to let's say a 1000W HMI. How the equivalence works out exactly will depend on a host of factors, particularly the emission spectra of the light sources that are being compared and the sensitivity and conversion efficiency of the receptor (in this case a plant). When it comes to plants, it will furthermore depend on what kind of plant and perhaps even what part of its growth cycle.

So there's really no quick & dirty way to equate X Watts of LED power to Y Watts of some other form of lighting.

Btw, about lumens: for applications like these, they're basically useless. The problem with lumens is that they are based on the sensitivity of the human eye, which peaks very strongly in the green part of the spectrum, i.e. around 525nm with a very broad bell curve tapering off to about 390nm (where UV starts) and about 680-700nm (where IR starts). Ironically, this green part that's weighed very heavily in lumen specs is exactly the bandwidth where photosynthesis virtually doesn't happen. For plant growth, particularly red and blue are relevant.

This means that if you would compare a 1000 lumen bulb that emits mostly green light will be pretty much useless for a grow light, whereas a source that emits only blue and red light and is also rated at 1000 lumens will be very much appropriate. If you plot out the spectra of these imaginary light sources and do some rough paper napkin calculations to work out how these two 1000 lumen sources compare in terms of absolute power radiated, you'd very quickly reach the conclusion that the lumen scale is totally unfit for choosing or designing narrow-band lighting systems for plant growth.

Not to mention that lumens are indeed a measure of flux and flux depends on (1) distance to the light source and (2) irradiance pattern of the light source (e.g. beam angle).

So lumens only sort of work if you compare broad-spectrum light sources intended for the human visual system with a similar irradiance pattern.


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Invisiblekoraks
Registered: 06/02/03
Posts: 26,667
Re: Question about Grow Light and Wattage. [Re: Kryptos]
    #28506337 - 10/16/23 03:11 AM (3 months, 10 days ago)

Quote:

Kryptos said:
Quote:

koraks said:
So there's really no quick & dirty way to equate X Watts of LED power to Y Watts of some other form of lighting.




I mean...Watts is the "quick and dirty" way--because Watts can be used to measure the electromagnetic flux coming off a bulb.



I see what I mean, but I think the issue here is that Watts are used inconsistently, and deliberately so. They're used as a way to express electrical power supplied to and dissipated by the LED or the incandescent bulb, and at the same time as a (very gross) approximation of the luminous flux emitted by the LED source. Since Watt is basically a unit that expresses an amount of energy per unit of time, it's a really flexible measure to use - but that also makes interpretations specific to contextual factors. Especially for consumers, this makes the whole thing kind of convoluted and confusing. Sadly, there's no good solution to it!

Quote:

To go back to my example of incandescent vs. LED bulb--filament are extremely efficient at converting electrical power to blackbody radiation, which is also a form of power. But it's very non-specific. So, 60W incandescent is giving off like, 50W IR and lower energy flux, 9W visible flux, and maybe 1W high energy wavelength flux. A 60W "equivalent" LED consumes 9W electricity and gives off 9W visible flux.



Yeah, in principle at least. Although LEDs aren't quite that efficient. For most high power LEDs, the efficiency is maybe 50% or so AFAIK; the rest is still dissipated as heat in the semiconductor junction itself.

Quote:


(pretty sure we're saying the same thing in various ways with varying amounts of detail, but that's okay because this discussion is meant to...illuminate...the subject for anybody that's passing by with a question!)



Sure; this discussion is not so much about disagreement but more about elaborating a couple of key points.


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