Germination test with the SANlight FLEX II 25

The optimal light intensity for cannabis seed germination

Overview

To define the optimal light intensity for the germination of cannabis seeds with the LED luminaire SANlight FLEX II 25, a practical test was set up and carried out in the internal laboratory. Seeds of the strain “Zombie Bride” were germinated in 77ér Eazy Plug trays. After germination, the plants were exposed to different light intensities; see Table 1 below.

Number of FLEX II 25	Light intensity [µmol/m²s]
2	100
3	160
4	200
5	280

Table 1: Number of FLEX II 25 with specification µmol

Over the following 39 days, it was observed how the plants developed under different light conditions. Various parameters, such as plant height, nodule spacing, and signs of stress, were documented. The experiment shows that the ideal exposure intensity for growing seed plants with the SANlight FLEX II 25 ranges from 160 – 200 µmol/m²s. Converted to an area of 1m², this corresponds to 105-140W / m² – when using the SANlight FLEX II luminaire. This optimal intensity and power were realized in the test using three or four SANlight FLEX II 25 per level of a CC trolley.

Recommendations

Four SANlight FLEX II 25 had the highest percentage of germinated and saleable seedlings. The advantage of this setup is the possibility to grow the plants under this light setup for a more extended period of time, as long as they are given enough space in the planes. The space limit was reached with 28 plants per level in 1.5L pots and 28 days of growth. It would need to be reduced to about 10-14 plants and one tier per CC cart removed to continue growing reasonably. After that, regular pruning in height and thinning of leaf mass is likely necessary to continue with this setup in the longer term. An example application would be micromothers.

The use of three SANlight FLEX II 25 can also be recommended. Here the percentage of plants with stress symptoms was below the setups with higher light intensity. It represents the famous “golden mean” and balances cost and performance. Even less experienced users will be OK with this setup.

Remark to the other setups

Using two SANlight FLEX II 25 can make sense under particular conditions. This setup may be appropriate when cost considerations are paramount, and longer seedlings with fewer nodes are acceptable. Plants under five SANlight FLEX II 25 have short nodal spacing, but the proportion of stressed plants increases. The margin for error is minimal, and any irregular growth will significantly affect the young plants. This setup should only be used when there is a great experience — the risk of breeding failures, high failure rates, and signs of plant stress increase. The higher purchase and operating costs should also be considered.

Description of experimental setup and procedure

To test the new SANlight FLEX II 25, seeds were germinated in several trays on CC carts and then exposed to different intensities. Germination and pre-growing on the standardized CC carts is common in horticulture, so we decided to use this test setup. The trays were not directly irradiated during the seed germination phase (3 days). After that, the various levels were exposed to two to five SANlight FLEX II 25 for 18 hours per day. After 11 days, the most vigorous plants were repotted into 1.5l pots and further grown under the respective intensities in an 18/6h light cycle for another 28 days. Table 1 and Figure 1 provide an overview.

Start date	End date	Days total	Description
22.11.2022	25.11.2022	3	Diffused light, seed in plugs
25.11.2022	05.12.2022	10	Vegetation phase 1 direct irradiation, seedlings in plugs.
05.12.2022	03.01.2022	28	Vegetation phase 2 direct irradiation, plants in 1,5l pots

To measure the influence of light intensity specifically, the remaining influencing conditions were kept the same on all levels. Each level of the CC trolley was equipped with an ebb & flood tray. Seeds were germinated in Eazy Plug CT77 trays, which contain plugs made of a coconut-peat mixture made explicitly for seed germination and rooting of cuttings. The number of SANlight FLEX II 25 lights used is listed in Table 2.

Number of FLEX II 25 [1]	Light intensity [µmol/m²s]
5 FLEX II 25	280
4 FLEX II 25	200
3 FLEX II 25	160
2 FLEX II 25	100

Table 3: Number of FLEX II 25 used per plane and their light intensities

Measurements

On 03.12.2022 (VEG DAY 8), the number of germinated plants, the number of valid leaf pairs (without cotyledons) the number of plants with signs of stress, deficiencies, and deformities were recorded.
On 05/12/2022 (VEG DAY 10), the number of saleable plants was counted. Here, all plants with vital, fresh, and uniform green appearance were included in the count.
On 03.1.2023 (VEG DAY 39), the height of the plants was measured, the number of nodules per plant was counted, and their subjective appearance was described.

Date	Measurements
25.11.2022	Germination rate
03.12.2022	Development rate, height, leaf pairs, stress symptoms.
05.12.2022	Classification of saleable seedlings in premium and standard quality
03.01.2022	Height, number of nodes, subjective appearance

Table 4: Date and target of the measurements

Measurements and results

The following section presents the results of the measurements.

Germination rate – 25.11.2022 (PRE VEG)

On 11/25/2022, the germination rate of all seeds was determined. The average germination rate for all levels was 91.3%.

Development rate – 03.12.2022 (VEG DAY 8)

On 03.12.2022 the development rate of all seeds was determined. All intact plants (also with signs of stress, etc.) were evaluated, which have developed since germination. Table 5 shows the development rate per level, including the number of lights used.

Number FLEX II 25	Development rate [%]
5 FLEX II 25	89,0
4 FLEX II 25	94,2
3 FLEX II 25	87,3
2 FLEX II 25	87,0

Table 5: The total number of seeds and their development rate in %.

Height / Leaf Pairs / Stress Symptoms – Dec 03, 2022 (VEG DAY 8).

On 12/3/2022, the following was measured for all plants:

Height
Number of leaf pairs
Number of plants with stress symptoms

Plants were categorized as stressed and non-stressed with the following appearances as signs of stress:

Red stems
Dark spots in the leaves
Light green to yellowish discoloration
Twist growth
Yellowing
Leaf deformations (thickening, curling)

Only valid leaf pairs were counted – without cotyledons.

Stress symptoms

The percentage of plants showing signs of stress was over 50% for five and four SANlight FLEX II 25. For three and two SANlight FLEX II 25 below 20%. Stress symptoms are not necessarily negative. They are a general indicator of plant activity and whether or not the processes involved are ideal. Increased plant metabolism brings the chance of faster development, higher yields, and the like, and at the same time, the risk of disturbances of the plant’s internal processes.

Number FLEX II 25	Number Plants	Stess symptoms		Symptom-free
Number FLEX II 25	Number Plants	Number	Rate [%]	Number	Rate [%]
5 FLEX II 25	274	152	55,5	122	44,5
4 FLEX II 25	290	162	55,9	128	44,1
3 FLEX II 25	271	41	15,1	230	84,9
2 FLEX II 25	268	51	19,0	217	81,0

Table 6: Number and rate of plants with and without stress symptoms

Height of plants and number of pairs of leaves

The lowest plants were recorded with Ø 3.6cm under five SANlight FLEX II 25. In the same proportion, as the light intensity decreased, the height of the seedlings increased.

Saleable seedlings – 05.12.2022 (VEG DAY 10)

On 12/5/2022, before the plants were planted in a pot with a growing medium, the seedlings were assessed and classified into three categories:

Premium quality (vigorous, vigorous, free from any kind of stress symptoms).
Standard quality (smaller than premium quality, slight signs of stress symptoms).
Rejects (not developed since germination, massive stress symptoms such as severe deformation, intense discoloration/spotting).

Figure 7 shows a tray dated 05.12.2022 with three examples color-coded in the image for each category:

Premium quality – marked in light green
Standard quality – marked yellow
Rejects – marked red

The percentage of premium-grade seedlings ranged from 50% to 69%. The most premium plants were recorded among four SANlight FLEX II 25 – among five SANlight FLEX II 25, the least plants fell into this category. With 90% sellable seedlings after ten days, the application of four SANlight FLEX II 25 was again ahead. The least plants could have been sold in total under two pieces of SANlight FLEX II 25 (79%).

Table 8 and Figure 5 on the following page show the figures in detail.

Number FLEX II 25	Premium Plants		Standard Plants		Saleable Plants total
	Number	Rate [%]	Number	Rate [%]	Number	Rate [%]
5 FLEX II 25	137	49,5	92	33,2	229	82,7
4 FLEX II 25	191	69,0	58	20,9	249	89,9
3 FLEX II 25	165	59,6	66	23,8	231	83,4
2 FLEX II 25	176	63,5	43	15,5	219	79,1

Table 8: Saleable seedlings by category

Vegetation phase 2 from 05.12.2022 to 03.01.2022 (VEG DAY 39)

After repotting 28 seedlings each on 05.12.2022 in 1.5L pots in growing soil (Plagron Light Mix), a 4-week rearing of the plants followed. Some pictures of this phase can be seen here.

Height measurement / number of nodes / subjective appearance - 03.01.2023 (VEG DAY 39)

On 01/03/2023 (VEG DAY 39), after 28 days under different light conditions, the height of each of the 28 plants in 1.5L pots per level and the number of nodules were measured per plant. The subjective appearance was also evaluated.

Plant height was over 30cm using five, four, and three SANlight FLEX II 25 (280, 200, and 160µmol/m²s) and about 26cm using two SANlight FLEX II 25 (100µmol/m²s). The seedlings under two SANlight FLEX II 25 were the highest of all levels (see Table 7) when measured after vegetation phase 1, and after vegetation phase 2, they were the lowest of all plants. This indicates insufficient light intensity – at first, the seedlings stretched into the light as they sought more of it and later lacked the energy for additional growth using two SANlight FLEX II 25.

The number of nodules per plant decreased steadily, with 8.3 nodes per plant when exposed to five SANlight FLEX II 25, and reached the lowest value of 6.3 nodules per plant with two SANlight FLEX II 25.

The data for this can be seen in Table 9.

Plants were consistently vigorous after vegetation stage 2 (28 days) when using 3 to 5 SANlight FLEX II 25, showing a healthy green and a strong stem. When two SANlight FLEX II 25 were used, the plants were also healthy but showed a lighter leaf green and had less leaf mass.

Number FLEX II 25	Ø Height[cm]	Ø Nodes/Plant	Ø Nodes spaceing [cm]
5 FLEX II 25	30,4	8,3	3,7
4 FLEX II 25	31,3	7,8	4,1
3 FLEX II 25	30,3	7,1	4,3
2 FLEX II 25	26,3	6,3	4,2

Table 9: Ø height of plants, Ø number of nodes per plant

Energy costs

Below are the energy costs calculated for the different lighting conditions.

Energy demand vegetation phase 1 – 25.11.2022 to 05.12.2023
Number FLEX II 25	Power [W]	Energy demand			Energy costs[€]
Number FLEX II 25	Power [W]	Total [kWh]	per Plant [Wh]	Per salable plant [Wh]	Total [€]	Per plant [€]	Per salable plant [€]
5 FLEX II 25	120	23,760	77,1	103,8	10,69 €	0,035 €	0,047 €
4 FLEX II 25	96	19,008	61,7	76,3	8,55 €	0,028 €	0,034 €
3 FLEX II 25	72	14,256	46,3	61,7	6,42 €	0,021 €	0,028 €
2 FLEX II 25	48	9,504	30,9	43,4	4,28 €	0,014 €	0,020 €

Table 10: Energy demand & costs at 0.45€/kWh vegetation phase 2 with 308 plants per level

Table 11 shows the energy requirements and energy costs for vegetation phase 2 after repotting in 1.5L pots with a growing medium and reduction to 28 plants per level.

Energy demand Vegetationsphase 2 – 05.12.2022 bis 03.01.2023
Number FLEX II 25	Power [W]	Energy demand		Energy costs[€]
Number FLEX II 25	Power [W]	Total [kWh]	Per Plant [Wh]	Total [€]	Per plant [€]
5 FLEX II 25	120	62,640	2237,1	28,19 €	1,01 €
4 FLEX II 25	96	50,112	1789,7	22,55 €	0,81 €
3 FLEX II 25	72	37,584	1342,3	16,91 €	0,60 €
2 FLEX II 25	48	25,056	894,9	11,28 €	0,40 €

Table 11: Energy demand & costs at 0.45€/kWh vegetation phase 2 with 28 plants per level

Germination + vegetation phase 1

Most plants developed into seedlings under four SANlight FLEX II 25 (94%). Also, under 3 SANlight FLEX II 25, 90% of the germinated plants are grown into seedlings. When five and two SANlight FLEX II 25 were used, the development rates were 89% and 87%, respectively. When three SANlight FLEX II 25 were used, the lowest number of stress symptoms (85% symptom-free) was recorded. The higher light intensities showed increased stress levels, with only about 44% symptomless plants. The height of seedlings after 8 days in the light was lower the higher the light intensity was. The number of saleable plants reached the highest value when four SANlight FLEX II 25 were used, as well as the number of premium plants. The worst cut here was the low light intensity.

Vegetation phase 2

The height of the plants after 28 days in the pot was, on average, between 30cm and 32cm under five, four, and three SANlight FLEX II 25 (280,200 and 160µmol/m²s). Plants under two SANlight FLEX II 25 (100µmol/m²s) averaged 26cm in height. The number of nodes decreased with decreasing light intensity. Thus, plants under five SANlight FLEX II 25 had 8.3 nodules per plant, and under two SANlight FLEX II 25 had only 6.3 nodes per plant. The calculated average node spacing was between 3.7 – 4.3cm.

Conclusion

The percentage of saleable seedlings and the results of vegetation phase 2 were both in very good and similar ranges when using three and four SANlight FLEX II 25. The energy costs were also in good relation to the higher and lower intensity. Accordingly, for applying the SANlight FLEX II 25 luminaire in CC trolleys, the use of four and three SANlight FLEX II 25 per level is the recommendation. More generally, this means that the ideal exposure intensity for growing seed plants with the SANlight FLEX II, is in the range of 160 – 200 µmol/m²s. Converted to an area of 1m², this corresponds to 105-140W / m². These values form the basis for designing and calculating corresponding breeding projects.