Stretching Seedlings

I'm not familiar with that light so I googled it.
first question I have is which version did you buy? the 3000k or 5000k?
with the stretch i'm guessing you have the 3000k. lower color temp is more red versus the more blue leaning 5000k. reds cause stretching. same as if you were to veg using an HPS light versus a MH light/ works, can be done, in fact i've gone seed to harvest with HPS light but it will stretch a lot - same as you are experiencing on your light.
This time of year, the light coming in thru your window, even though it may be less intensive, is actually a better color temp than your light is for the phase of growth your plant is in. on the opposite end, when it comes time for flowering your 3000k light will be much better than the window because of it's intensity.

at least that's how i'm reading it, I may be wrong.......

 

my apologies, i read the info much too quickly and assumed it was choice of color temp on the light, not both with a switch. that's what happens when you "assume".
I hope you find the answer my friend. sorry i wasn't of more help to you.

 

There could be more sunlight than you think.
Full sunlight is over 100,000 lux, and overcast skies are a significant fraction of that.
The grow light instructions usually recommend less than 10,000 lux for seedlings.
I recently germinated seeds under full blurple lights, veg+bloom with seeds in RapidRooters, and there was no stretch.
Seeds germinated under the same light, but dimmed down to 10,000 lux stretched a lot.
I now believe seedlings can handle full lights if they are subjected to it before sprouting.