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lighting More about hours of lighting

W

wordwiz

AJ,

As promised!

In the other thread, the conversation about how long to leave the lights on came up. Continuing that:

Hopefully, my Siletz toms will actually self pollinate so I can test the light theory (12, vs. 14, vs. 16, vs. 18 hours per day) this spring/early summer.

A trivia side note: if one is growing under lights with the intention of selling produce, using a 150 watt bulb, it would cost $2.70/mo. more running 18 hours rather than 12. That would equate to about two pounds of tomatoes per month more. That's not a lot.

Something else in this arena: I have plants at the office (tomato and lettuce, with one extremely leggy green bean!) that get no artificial light and only direct sunlight for maybe six hours a day, max. In the few days the plants have been there, we have had as many days of completely overcast days as sunny days. Yet the lettuce and the tom seem to be growing nicely. This leads me to wonder if I could get away with maybe four hours of lighting per day in a south-facing greenhouse? That would save me $36 per row of lights per month. Maybe run them from 6-8 am and pm each day in the dead of winter, 6-7 am and 7-8 pm.

I love the idea of experimenting to find out!

Mike
 
Mike...go for it man..I think its a good idea....I turned off my CFLs in the grow box for 6 hours today but now they are back on for heat....the grow box is doubling as a germinator right now....
 
I'll be sure to post my results. "The Engineer" has already read my plans as far as controls go, so the results should be somewhat valid.

About the only thing I have not settled is whether to use one 150 watt HID lamp or two 105 watt CFL bulbs per plant. Probably the HID because of the heat factor. It puts out about 1,000 more lumens, uses 60 watts less per hour but also provides heat, which would be a major factor in a GH during cold weather.

Mike
 
It would be interesting to see what the difference is between less hours of light per day and less intense light for a normal period. My theory is that total darkness might be preferable to weak light if you want to avoid legginess.
 
Just checked the amount of light I'm getting on a overcast day - between 10,000-12,000 lux. That's about the same as a 150 watt HPS light placed 18" away. When the sun did pop out, and it is still rather low on the horizon, ~41 degrees, I get a reading of 65,000 lux.

One other tidbit to throw into the equation, and I realize the maturity of the plant has significant bearing - tomatoes and peppers seem to produce most of their fruit from the middle of August to the middle of September in the Northern Hemisphere. The amount of daylight then varies from 14 hours (August 9) to 12 hours (September 25)

Mike
 
Isn't the precise amount of daylight dependent on latitude as well? I know my friend in upstate New York and I have compared notes, he's about 8 degrees of latitude further north than I am, and it gets darker earlier in the winter and stays light longer at mid-summer than it does here in South Carolina.

So before you get too far gone in your light geekery, remember that there are a lot of variations in the length and quality of light as you move from location to location, and yet nearly all of us manage to produce hefty harvests of peppers.
 
I am more concerned with the transition from indoor to out.

I give mine 15 or so hours a day.

Last year when I put the plants outside, the existing growth went dormant on some plants, while new growth sprouted out of a few places and took off.

I assumed that it was due to differing light, either hours or lumens, and that the old vegetation was not well suited to the new light, and that the new growth (which made some plants lop-sided) was better suited and therefore far outpaced the existing.
 
Pam,

My experiment with the number of hours of light per day will not rely on latitude, clouds, etc. If the tomatoes set fruit inside, I will weigh the produce to see how the amount, in hours per day, of light affects production. I'll also post pics showing the growth of plants.

This whole thing is based on how many of light per day is best, good, or necessary for plants to grow.

Mike
 
wordwiz said:
Just checked the amount of light I'm getting on a overcast day - between 10,000-12,000 lux...
Click to expand...

What kind of meter are you using? I think I have an old exposure meter for a film camera around somewhere. I'd like to be able to compare my light boxes and outdoor light.
 
wordwiz said:
I'll be sure to post my results. "The Engineer" has already read my plans as far as controls go, so the results should be somewhat valid.

About the only thing I have not settled is whether to use one 150 watt HID lamp or two 105 watt CFL bulbs per plant. Probably the HID because of the heat factor. It puts out about 1,000 more lumens, uses 60 watts less per hour but also provides heat, which would be a major factor in a GH during cold weather.

Mike
Click to expand...


If I were you, I'd use the 1 150 watt HID for the reason that...

Using 2 CFLs may create a small difference in between the plants under 1 CFL and the plants under another.

For example, not all CFL bulbs are exactly the same so one may have 100 lumens less than the other out-of-the-box
 
caroltlw said:
What kind of meter are you using? I think I have an old exposure meter for a film camera around somewhere. I'd like to be able to compare my light boxes and outdoor light.
Click to expand...
It's a LX1020B Digital Lux Meter. One of the best investments ($34 or so) that I have made.
groeatrepeat said:
If I were you, I'd use the 1 150 watt HID for the reason that...
Click to expand...
Actually, I was thinking that if I am going to spend money on lights, it might as well be something I can use in a Greenhouse. I love the CFL bulbs but even with a reflector, their light seems to diffuse more. I don't see them as being worth as much in a GH for this reason. I can buy two more CFL bulbs, at a cost of about $60 counting the fixtures I will need, vs. $90 for the two HID fixtures. When I factor in the cost of electricity for 90 days, the HID lights are a whole $2 cheaper.

Mike
 
wordwiz said:
It's a LX1020B Digital Lux Meter. One of the best investments ($34 or so) that I have made.
Click to expand...

That's cheaper than I thought. OK, one of those goes on my wish list for when I hit the right Lotto numbers. :)
 
Cool. I was just searching eBay and found a cheaper one that only goes to 50,000 - which would only be good indoors since you're getting 64,000 outside. Glad I didn't go for that.
 
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