Down the terminology rat hole, final.
We have been using HID lights for years and these lights were originally designed to aid human eyesight in areas of limited or no ambient light. The output of these lights are described in 'lumens'. Unfortunately a lumen is, in engineering terms, a relative term that refers to how well a light will assist human eyesight. Across the photometric visible spectrum which both humans and plants utilize, the human utilization curve is virtually the inverse to that of the curves in the red and blue spectrum that the photosynthizing portions of the plant utilize. Lumens, and virtually all other human eye related metrics refering to the quality of light, including CCT and CRI, are terrible indicators of how a light source will perform in a horticultural application. These terms are how a manufacturer who is designing a light source for the human eye would describe the technical qualities of the light. My first indoor grow was in '82 or '83 in the great Pacific Northwest, so I too 'grew up' using the term 'lumen'. It took a long time before a friend (who was really a genius with these things) finally pounded it into my thick skull what a useless term the lumen really was for horticultural applications. Yet the term lumen persists, firmly entrenched in the terminology rat hole.
So now we move on to LED's, which from a pure technical standpoint, should easily be the most controllable and efficient form of light for horticultural applications- even better than the CMH bulb as described in this thread. And we find ourselves heading right back down a descriptively meaningless terminology rat hole, only this time the rat hole word is 'Watt'. Watt is, yet again, a poor indicator of the quality of light that a fixture is providing. And it does not have to be this way, as the quality of light (any light) can be described using two terms- wavelength and amplitude. Wavelength describes the relative energy level of the photon itself, and Cla/ Clb are tuned to specific wavelengths. Amplitude tells you how much of any particular wavelength you have. Simple- wavelength and amplitude, wavelength and amplitude, wavelength and amplitude. These two metrics can be easily shown with a simple photometric chart which shows radiant output in terms of true photon count (umol) or energy level (Watt). Either is fairly indicative of the quality of light- photosynthesis is a photon driven event, therefore photon count (umol) could possibly be argued to be better. Also- the indication needs to be absolute, not relative- relative indications, as shown in the CMH chart on page 83, make the CMH look 'shitloads' better than than the HPS at the right side, which, if shown in true absolute terms, would NOT be the case. NOTE THE TERM 'RELATIVE ENERGY' ON THE Y AXIS OF THE CHART. This is how they trick you with charts.
OK- back the LED and the Watt- again, Watt as it seems to be used in the marketing of these lights is a terrible term by which one can judge the quality of the actual light output of the system. An example as follows:
Wouldn't these be better described and marketed as '1.7' and '1.3' Watt 'arrays', 'modules', or perhaps 'light engine'? This is just an observation- I am not ragging on this guys lights, but it is an observation that any design guy familiar with LED technology would point out. To say they are '3W LEDs' leads to all the confusion regarding power that you can clearly see when following this thread thru start to finish. Also, I take issue with describing muti-element LED arrays as 'LEDs'- a true 1W or 3W or 5W 'LED die' is a totally different animal in terms of efficiency and light output compared to an array composed of 3, or 4, or 5, or whatever, individual, 1/4 or 1/2 Watt LED dies- yes, there is a huge difference.
Finally- 'Watt' is a terrible descriptor of performance for an LED because the efficiency of the individual LED's themselves- efficiency = electrical power in vs. radiant power out, is highly variable and dependent upon (1) LED process and materials (the best 'red' are worse than the the best 'blue' by a factor of at least 3x, and the gap is growing daily) (2) bin code (3) junction temperature, and (4) forward current.
Again- the only way to know for sure is to see the photometric output chart, in absolute terms. I cannot say this enough, because it is the simple truth, and everyone interested in LED technology should know this fact. Any repectable LED maker should have this information readily available- either from a spectroradiometer or an integration sphere- we have several versions of both- this is simple, basic engineering equipment in the LED design field.
So everyone can get mad at me for this message and yell at me- I am married so I am accustomed to it. Still a big Seattle Seahawks fan, so you can see the level of abuse I can tolerate. If you can keep your argument strictly to the technical merits of what I have had to say, I am OK.
Thanks again Sun for the fantastic grow. Looking forward to more great work guys like you and Irish and the other guys have done for the humble LED.
.
