Does light height really matter on a diamble fixture ?

[mmxk]

Hi guys, I always wondered if light height from a dimable fixture actually really matter? Let's take these 2 example and explain me if there is a real difference to the plant. I will use totally fictive numbers for a seedling.

Example 1: Fixture at 100% intensity at a distance of 48" producing 200 μmol/m2/s at the plant.

Example 2: Fixture at 25% intensity at a distance of 18" producing 200 μmol/m2/s at the plant.

Obviously, energy consumed and heat output will be different when a fixture is running at 100% vs 25% but I'm not too concerned about these 2 factors.

[oldjarhead100]

yes it does matter if you ran the light at 25% at 48 inches your plants would stretch like theirs no tomorrow ,If you are adjusting the height when you adjust the light output then your all set .

If you have the height to run it at full cap. why would you not run it at max. I also think (personal opinion no facts) that if a plant gets used to a light output, changing that output really stresses the plant out

[mmxk]

I'm not sure if seedling would really stretch more as the distance increase for the exact same ppdf.

I go overboard but let's take the example of outdoor plants. The sun will provide a specific ppfd at a moment in time while been millions of miles away and that wouldn't influence the plant to stretch more than a plant receiving the exact same ppfd at either 48" or 18".

I'm in the seedling phase right now and my plants get a 15-20 ppdf increase each day. When the seeding same will be completed (3 set of true leaves) I will be around 250-280 ppfd.

[Rwise]

I have read that reducing the output changes the light spectrum output of the light and shortens its life. IDK how that may apply to LEDs

[Obi-Wan]

You also need to consider the coverage area. When the light is raised it decreases intensity but increases the coverage area. The opposite is true when the light is lowered, intensity increases but the coverage area decreases. While you can adjust the intensity with the dimmer, the coverage area will always be tied to the height of the light. The key is to balance intensity and coverage area to find the height that maximizes both in your space.

[oldjarhead100]

well said Obi-wan

[mmxk]

Your point is valid but I'm absolutely not worried in coverage area in the seedling phase. All I need in a 1 square inch of coverage per plant right now. I can have that coverage at 1" height all the way to 6'.

[mmxk]

Thanks everyone for your comments. I went safe and lower my diamble fixtures but I kept the same ppdf at the canopy for the day. The next day I boosted the light power to increase the ppdf by 50 umol/s.

The one and only 1.5 week old seedling that wanted to stretch slowed down a bit. The other 3 seedlings are not stretching too much.