converting sauna --8 bulb T5 HO --too much?

[dshallpost]

Thank you Naoki Are the Bridgelux the same as the Sunblaster with respect to the spectrum?

[naoki]

You can choose from 3000-5700K. Sunblaster is 6500 or 4100K. The EB strip I linked earlier is 4000K, which would be my choice. In general, 3000-4000K is probably slightly better (photosynthetically more efficient) than bluer ones (from my calculation).

For a given number of photons, red light is more efficient for photosynthesis than blue light. If you use the lumen numbers (which is relevant to human eyes but not for plants), you get a higher efficacy (lumen/W) from higher K (bluer light). With known emission spectra (from data sheet), we can convert this lumen/W to the efficacy relevant to photosynthesis (incorporating the fact that red light is more efficient for photosynthesis). Here I'm using yield photo flux (YPF) efficacy. YPF is similar to photosynthetic photon flux (PPF), but YPF put more weights to red light.

EB Gen 2
3000K 2.52 micormol/s/W (175lm/W for human)
4000K 2.55 micormol/s/W (180lm/W)
5000K 2.44 micormol/s/W (180lm/W)

I'm using the spectra from older Bridgelux Vero v1.2. So it is not exact for the newer EB. Also I should note that I had only 70CRI spectrum for 5000K, but EB Gen2 is CRI 80, so 2.44 is an underestimation for 5000K. The values above show 4000K is slightly more efficient than 3000K, but with newer versions, 3000K is slightly higher than 4000K.

The general trend should be similar, the efficiency for plant photosynthesis is similar, but generally more efficient with lower K (more red).

So it is weird to see that some companies are trying to use 6500K for grow lights. I'm not sure if they do any research, but I'm guessing that they are hoping that people don't know the difference between lumen and photon flux for plants. So with 6500K, they can say they have high lumen/W even though plants don't care about lumen. Grow light companies who know about plants tell us about PPF, not lumen.

[dshallpost]

Just to follow up: I bought LED lights. Now I am wondering if there is some rule of thumb about translating from natural light to growing under lights. Thank you to Ray, who posted a while back explaining that the requirements posted for sunlight usually refer to peak light, and that you will not need those peak light level FC under 16-hour consistent artificial light. But how much less do you need? May be I will start a new thread . . . .