Is this a heat from lights issue?

[MisterEd]

I checked these plants about 3 hours ago and they looked perfect. Just went in and two of them had this brown discoloration; only on top side of leaf. They were transplanted yesterday with no issues into 1 gallon pots from their seedling containers. They are just shy of three weeks old. No nutes, just plain rainwater added to soil. MH 400 is 10" above plants and passed 'hand
test.' I raised it another inch. If it was a heat issue I would expect to see the newest growth at the very top to suffer first and most. Or could this be a reflected light issue? Pics attached.
thanks,

Bra

 

[Diggler420]

10” may be too close. Raise it up to 20-24” and let her recover some.

 

[MisterEd]

10” may be too close. Raise it up to 20-24” and let her recover some.

 

[MisterEd]

ok. Evidently the 'hand test' is not foolproof. Lol

 

[DaddyKush]

A 400w metal halide will definitely produce a lot of heat. It looks like maybe you spilled some water on the leaves and that caused the light to burn the leaves, that's likely what the spots/discoloration are. I do see some other signs of heat stress.

How big is the grow room? You'll need lots of ventilation, particularly if you have a powerful HID light in a small grow area. I'd want some type of smaller fan inside the grow room blowing over the canopy, as well as an exhaust fan bringing in constant cooler air while also exhausting the hot air.

 

[MrSauga]

If you can afford an inexpensive light meter then you can measure the lux for each stage of growth. You can get an app to do the same but I hear they are not that accurate.
This way you'll never burn or cause light stress to your plants again.

HOW MUCH LIGHT DO YOUR CANNABIS PLANTS REQUIRE?

• Clones and seedlings: 5,000–7,000 lux
• Vegetative growth: 15,000–50,000 lux
• Flowering: 45,000–65,000 lux
• Maximum recommended amount of light: 75,000 lux

Source

 

[MisterEd]

If you can afford an inexpensive light meter then you can measure the lux for each stage of growth. You can get an app to do the same but I hear they are not that accurate.
This way you'll never burn or cause light stress to your plants again.

HOW MUCH LIGHT DO YOUR CANNABIS PLANTS REQUIRE?

• Clones and seedlings: 5,000–7,000 lux
• Vegetative growth: 15,000–50,000 lux
• Flowering: 45,000–65,000 lux
• Maximum recommended amount of light: 75,000 lux

Source

Thank you Mr. Sauga for your infomative post! A big slice of raisin pie if you are so inclined. Lol

Bra

 

[MisterEd]

A 400w metal halide will definitely produce a lot of heat. It looks like maybe you spilled some water on the leaves and that caused the light to burn the leaves, that's likely what the spots/discoloration are. I do see some other signs of heat stress.

How big is the grow room? You'll need lots of ventilation, particularly if you have a powerful HID light in a small grow area. I'd want some type of smaller fan inside the grow room blowing over the canopy, as well as an exhaust fan bringing in constant cooler air while also exhausting the hot air.

 

[MisterEd]

Thanks DK. I have ventilation and air circulation currently. Adding two more circ fans in a couple days.

 

[MisterEd]

If you can afford an inexpensive light meter then you can measure the lux for each stage of growth. You can get an app to do the same but I hear they are not that accurate.
This way you'll never burn or cause light stress to your plants again.

HOW MUCH LIGHT DO YOUR CANNABIS PLANTS REQUIRE?

• Clones and seedlings: 5,000–7,000 lux
• Vegetative growth: 15,000–50,000 lux
• Flowering: 45,000–65,000 lux
• Maximum recommended amount of light: 75,000 lux

Source

Just got my Lux meter in today and my plants were getting more lumens than I realized! 40-50k and I was surprised that lumens are higher around the periphery and not directly below the bulb. Another tool to dial in a grow.

 

[MrSauga]

Just got my Lux meter in today and my plants were getting more lumens than I realized! 40-50k and I was surprised that lumens are higher around the periphery and not directly below the bulb. Another tool to dial in a grow.

Excellent! So always start at the low end of the lux scale for the stage the plants are at then increase until you find that sweet spot, again at each stage.