The height of the grow light has a significant effect on the depth of irradiance (PPFD) penetration below the canopy top.
The following tables illustrate how keeping the irradiance at the top of the canopy at 500 µmol/m²/s and varying the grow light height affects the level of irradiance into the canopy. Inch by inch.
The height of the grow light should be increased as the canopy gets higher. The intensity of the LEDs should be adjusted for each height.
As the height of the grow light over the canopy is decreased so does the depth of penetration into the canopy (keeping the intensity of the grow light constant at the top of the canopy).
Height=40
D | ppfd | % |
0 | 500 | 100 |
1 | 476 | 95 |
2 | 454 | 91 |
3 | 433 | 87 |
4 | 413 | 83 |
5 | 395 | 79 |
6 | 378 | 76 |
7 | 362 | 72 |
8 | 347 | 69 |
9 | 333 | 67 |
10 | 320 | 64 |
11 | 308 | 62 |
12 | 296 | 59 |
Height=35
D | ppfd | % |
0 | 500 | 100 |
1 | 473 | 95 |
2 | 447 | 89 |
3 | 424 | 85 |
4 | 403 | 81 |
5 | 383 | 77 |
6 | 364 | 73 |
7 | 347 | 69 |
8 | 331 | 66 |
9 | 316 | 63 |
10 | 302 | 60 |
11 | 289 | 58 |
12 | 277 | 55 |
Height=30
D | ppfd | % |
0 | 500 | 100 |
1 | 468 | 94 |
2 | 439 | 88 |
3 | 413 | 83 |
4 | 389 | 78 |
5 | 367 | 73 |
6 | 347 | 69 |
7 | 329 | 66 |
8 | 312 | 62 |
9 | 296 | 59 |
10 | 281 | 56 |
11 | 268 | 54 |
12 | 255 | 51 |
Height=25
D | ppfd | % |
0 | 500 | 100 |
1 | 462 | 92 |
2 | 429 | 86 |
3 | 399 | 80 |
4 | 372 | 74 |
5 | 347 | 69 |
6 | 325 | 65 |
7 | 305 | 61 |
8 | 287 | 57 |
9 | 270 | 54 |
10 | 255 | 51 |
11 | 241 | 48 |
12 | 228 | 46 |
Height=20
D | ppfd | % |
0 | 500 | 100 |
1 | 454 | 91 |
2 | 413 | 83 |
3 | 378 | 76 |
4 | 347 | 69 |
5 | 320 | 64 |
6 | 296 | 59 |
7 | 274 | 55 |
8 | 255 | 51 |
9 | 238 | 48 |
10 | 222 | 44 |
11 | 208 | 42 |
12 | 195 | 39 |
Height=15
D | ppfd | % |
0 | 500 | 100 |
1 | 439 | 88 |
2 | 389 | 78 |
3 | 347 | 69 |
4 | 312 | 62 |
5 | 281 | 56 |
6 | 255 | 51 |
7 | 232 | 46 |
8 | 213 | 43 |
9 | 195 | 39 |
10 | 180 | 36 |
11 | 166 | 33 |
12 | 154 | 31 |
Height=10
D | ppfd | % |
0 | 500 | 100 |
1 | 413 | 83 |
2 | 347 | 69 |
3 | 296 | 59 |
4 | 255 | 51 |
5 | 222 | 44 |
6 | 195 | 39 |
7 | 173 | 35 |
8 | 154 | 31 |
9 | 139 | 28 |
10 | 125 | 25 |
11 | 113 | 23 |
12 | 103 | 21 |
Height=5
D | ppfd | % |
0 | 500 | 100 |
1 | 347 | 69 |
2 | 255 | 51 |
3 | 195 | 39 |
4 | 154 | 31 |
5 | 125 | 25 |
6 | 103 | 21 |
7 | 87 | 17 |
8 | 74 | 15 |
9 | 64 | 13 |
10 | 56 | 11 |
11 | 49 | 10 |
12 | 43 | 9 |
As the "Height From" is decreased to "To Height" the intensity at the top of the canopy is adjusted to the PPFD entered.
Column Descriptions
D = Depth, distance below the top of the canopy
ppfd=Irradiance at that depth
%=Percentage difference between PPFD at that depth comparded to the PPFD at the top of the canopy.
Increment = Increments that the Height is decreased.
Input Descriptions
Height From: Starting height above canopy. Must be greater than "To Height".
To Height: Ending height. From and To define the range of heights to view.
Increment: set to 1 to see all heights in your selected range. Increase to skip some.
PPFD: The desired PPFD at the top of the canopy.
Max Depth: How many inches into the canopy you want to view.