Too Much Light?

cogitech · December 4, 2019, 10:14pm

Holy crap! I was just reading @Foreigner’s thread about building a new light and I realized I’ve got way too much light in my tent, according to the math I see in that thread. Question is, is this a “bad” thing?

My tent is 36" by 20" which works out to 5 sq. ft. and I have ~375 (real) watts of LED in there (~195w blurple + 180w of Citizen CLU048-1212C4 3500k COBs).

So that’s 75W per sq.ft. The COBs alone are pushing 22,000 lumens and the much less efficient blurple is good for another 12,000 lumens.

Is there such a thing as too much light? I mean, aside from the obvious bleaching or burning risks?

Grease_Monkey · December 4, 2019, 10:17pm

Lol I’m at 85 watts in 1.45 square feet (too dump to do the math to get that to per square foot)

cogitech · December 4, 2019, 10:18pm

You are at 58w per sq. ft.

Grease_Monkey · December 4, 2019, 10:19pm

What’s the equation for that lol

cogitech · December 4, 2019, 10:20pm

85 divided by 1.45 = 58.62 (so 59w if you round up, actually).

Grease_Monkey · December 4, 2019, 10:21pm

Damnit… that was way to simple lol

crazaer · December 4, 2019, 10:24pm

420 characters

Jetdro · December 4, 2019, 10:33pm

Not versed in LED, never run one. I do KNOW that with my HPS bulbs, 50 watts a foot is all I can use, anymore is a waste or light has to be 30 inches up. I have heard LEDS need less watts per foot.
My last run, my light was too close, too hot and I got a lot of fox tails…NOT caused by excess N. Heat wasnt too bad either, so thinking the intensity was a bit high.

cogitech · December 4, 2019, 10:39pm

This is a good point of reference, thanks! As you say, LED is more efficient so my 75W per sq. ft. is definitely too high.

I can drop that down considerably by killing the veg switch on the blurple, but I need to keep at least the bloom switch on the blurple because the fans in the blurple cool the COB heat sinks.

Hmmm, so I’d be down to about 100w on the blurple and 180 on the COBs, so 280w which would still be 56w per sq. ft.

That’s my only option right now, and I’ll raise the lights up a bit more.

Foreigner · December 4, 2019, 10:43pm

As long as you are not burning your plants, or care about how much power you use, I see no issue with too much light apart from waste.

I’m thinking about sunlight re: hardening off plants to sunlight. They can take it, just give it to her slow.

Now that I think of it I’ve had plants not enjoy midday sun too.

cogitech · December 4, 2019, 10:45pm

Well, electricity is cheap AF where I live but I don’t really like to be wasteful, either. I’ve realized that based on @Mr.Sparkle’s advice in your thread (35-40 watts per sq. ft.) I could grow just fine with only the COBs in there. It would give me exactly 36 (extremely good) watts per sq. ft.

Foreigner · December 4, 2019, 10:45pm

Also, your blurple lights are probably so inefficient that your could downgrade their actual wattage by, say, 50%. That could account for you thinking your wattage is inflated.

slain · December 4, 2019, 10:46pm

I know it’s only a half arsed measure but as a rule of thumb I have always worked on the principle that any more than 8 -10k lumens per square foot doesn’t do much but burn power causing more trouble that it’s worth… heat, bleaching etc… so that works out around 50w per square foot if using current state of the art LED’s at 180-200 lumens per watt, give or take a bit.

cogitech · December 4, 2019, 10:53pm

Thanks everyone. All good points.

I’m going to kill the veg switch and not think about it much more. The plants will tell me if they appreciate it or not.

In the future I will use veg switch plus COBs for veg, and bloom switch + COBs for flowering.

Foreigner · December 4, 2019, 11:03pm

Efficiency is definitely the best metric. My current veg light is 105w. I expect my 80 watt hypothetical rig will be twice as powerful as the old.

The only downside I see to only using the cob could be less coverage.

cogitech · December 4, 2019, 11:27pm

It’s 5 COBs at 36 watts each (@ nominal current), so the coverage is spread out fairly well in the space. However, I have been considering the idea of picking up another COB to make it an even 6, and then pulling apart my “frankenlight” (AKA “COBlurple”) and setting up the COBs on a proper frame. Maybe in the new year…

Foreigner · December 4, 2019, 11:34pm

I see. That makes way more sense.

36w sounds lower than cobs I’m familiar With. I see 50 and 100ish.

Do they still require a massive heatsink?

slain · December 5, 2019, 12:16am

Most cobs without any additional optics etc will have a reasonably standard spatial distribution similar to this:

Lenses/optics can help a lot with 'hot spot" issues I’ve found from experience… ledle have a broad range of optics that can be used to give you a more even distribution, from diffusion lenses to those that will direct ligth of cobs along the edge of the grow space towards the plants, rather than the wall of the tent… this issue, along with the heat output was partly why I eventually swapped over from cree’s to strips, but you can get more use of your ligth output with these kind of optics.

CPU heatsinks

cogitech · December 5, 2019, 12:29am

They are 100 watt COBs but the efficiency sweet spot and longevity is ideal right around 36 watts (36 volts x 1080mA). I designed the solution based on Citizen’s PDF of specs. People who run 50 watt COBs at 50 watts puzzle me.

cogitech · December 5, 2019, 12:32am

The spacial distribution of light isn’t a big worry for me at all. 5 COBs in a space this small - everything is covered, with tons of overlap.