Using ASTM Solar Spectrum Data to compute the right led lamp

Hello,

So, here is my reasoning to design my DIY led lamp

• First assumption :

As I want to made an indoor grow, I want to have the same irradiance than the sun can do. Perhaps 25% more to see if I can improve the final amount

• Second assumption :

As the range of wavelength for photosynthesis is approximately from 400 nm to 800 nm, I only need the sun irradiance in this range

• Third assumption :

As green and yellow wavelength (500nm to 600 nm) are not as important as the Blue and Red ranges, I only need the sun irradiance from (400 nm to 500nm & 600 to 800 nm). This is an approximation

The maximum sun irradiance on eath is 1413 W/m² (see ASTM G173-03) at the top of the atmosphere.

From ASTM G173 data, I can compute the influence of each wavelength (280 to 4000nm 0.5nm precision) and the quanta provide by each of these wavelengths.

So, if I compute irradiance from 400 to 800 nm, it's give me 678 W/m² and 335 umol/m²/s.
If I substract the 500 to 600nm bandwidth, the irradiance is only 480 W/m² and 253 umol/m²/s.


So to reproduce the sun in my setup, I need 678 W/m² if I want all spectrum from 400 to 800 nm.
I added 25% more so 847,5 W/m².

If I don't want 500 to 600 nm bandwidth, I only need 480 W/m² +25% = 600 W/m²

Is this reasoning is a good approach ?

Yours,

Michael

Hello & welcome,

To summarize the approach, the idea is to have the same amount of red and blue light that the sun has in outer space, plus 25%.

That is way way way too much power. The plants would nearly incinerate. A good target for the amount of light is 800 umol. Higher than this and plants can start to get burned. To compare, the brightest sunlight at sea level is about 2000 umol. Plants that live outdoors can cope with that because they have become hardened by the UV radiation in the sunlight. This hardening works across the whole spectrum, making the outdoor plants more resilient against bright light (but also less efficient at photosynthesizing).

What I found very helpful when learning about the stuff is this very good read.

Btw I noticed your umol results are a factor 10 too low, should be about 5x the power in W/m2 for a white spectrum.

600 W / (m^2) = ~55.741824 W / (ft^2)
Not bad, most suggest 30-60W/ft^2, but this is at the wall and assuming the efficiency of the LED components we're using is approximately 40%, although it's probably less in most instances. So, if we assume that 600W/m^2 is actually observed by the plants and that our LED's are 40% efficient, this means you'd have ~90W/ft^2 at the wall. Quite a bit of light, imo. Not sure if plants would be incinerated, but as far as I can guess they would probably show signs of light stress.

GL, grower.

You are right, I forgot one zero for the umol/m²/s values ! Thank you corrected me !

Ok, using outer space irradiance is too much so, I will use "Global Tilt" values ( "Global Tilt" = spectral radiation from solar disk plus sky diffuse and diffuse reflected from ground on south facing surface tilted 37 deg from horizontal).

For full spectrum GT irradiance is approximately 1045 W/m² - 6736 umol/m²/s from 280nm to 4000nm
For the band 400 to 800 nm GT irradiance is is approximately 567 W/m² - 2804 umol/m²/s
For the band 400 to 800 nm except 500 to 600 nm GT irradiance is is approximately 410 W/m² - 2082 umol/m²/s

So for Ee: 410 < Ee (W/m²) < 567
& for quanta : 2082 < Quanta (umol/m²/s) < 2804

Next step, using Chlorophylle A-B, Beta Carotene and Phytochrome peak to reduce the irradiance qty.

Bumping Spheda said:

600 W / (m^2) = ~55.741824 W / (ft^2)

Click to expand...

600W of pure light would be equivalent to for example 12 of the new A51 panels, to give some idea of the magnitude.

I built a little led grow lamp, but as I am not as good in biology as I am in electronic, I try to adjust this setup to match perfectly with veg and flow.

So here are the specs of my setup:

395-400 nm > 14.35 W/m² - 50 umol/m²/s
405-410 nm > 14.35 W/m² - 51.65 umol/m²/s
442 nm > 14.32 W/m² - 23.4 umol/m²/s
528 nm > 10.13 W/m² - 45.37 umol/m²/s
623 nm > 7.61 W/m² - 40.24 umol/m²/s
656 nm > 42.0 W/m² - 233 umol/m²/s
724 nm > 6.0 W/m² - 38 umol/m²/s

Total : 108.81 W/m² - 512 umol/m²/s - Radiant Power 44.7 W - Power consumption 161 W at 0.5 meter high
Irradiance is one-axis and &#920; 80°
All channels can be dim.
Min efficiency 27.8%

I think I will divide this setup by two.