How close to light?

4 years ago

last modified: 4 years ago

Happen to have at least 2 pots of same plants - see how much difference is there because of distance to light source.

In each photo, plant on left is very close, only about 2.5" from CFL lightbulbs. Plant on right is about 6" away; there is lots of difference in color of the leaves:

Plant with etiolated inflorescence and almost no red on margins (right pic) is about 7-8" away:

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Comments (4)

Rob Blomquist
4 years ago
Let's not talk of CFL light bulbs so simply, let's also talk watts and color. I use a 150w CAL for seeds, they are fine about one foot away from seedlings. I would say 6 inches to a foot is a good operating range. Maybe it's time for a new bulb.
rina_Ontario,Canada 5a
Original Author
4 years ago
last modified: 4 years ago
Distance mentioned above may be too close for some plants, but not for plants in photos.

CFL bulbs I use are 23W (equivalent to 100W incandescent), and few are higher. They are all daylight, 6500k and each is 1500lumens. I have different lights - LED bulbs and tubes, few T8 fluoros and also T5HO. Plants in photos are under 23W CFL bulbs. Most of my plants are that close, but they are well acclimatized to these lights. Many are new - I just changed couple that burned out. This is only my experience, and I have been using them like this for past 4 years. I had lights before, but plants were further away. Lights are on timers, on for 12hrs.

Here is another shelve. Mostly haws and gasterias. LED tubes are 12W, 5000k, 1550 lumens. They are about 8" away. That distance seems to be good for them, but few Topsy Turvy echeverias have to be moved - they are etiolated:

This Senecio haworthii is under same lights (haws and gasterias are visible on each side) but closer because it is taller plant. Distance is 3.5" from light source. Maybe it could be closer, seems to me that it could be more compact. But there is new growth where branches were decapitated:
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mindshift
4 years ago
As light travels away from the bulb it disperses. The light emitted by the bulb is measured as lumens. When light illuminates an object the illumination is measured as lux. 1000 lumens from an LED bulb provides some 31,831 lux at 0.1 meter (just under 4"). At 0.2 meters the lux falls to 7,958.

CFL bulbs put off more heat than LED bulbs, but they are still cooler than incandescent bulbs. In my experience, as long as the plant does not touch a CFL bulb it won't get scorched. If a plant isn't getting enough light you can use higher wattage/lumen bulbs to get more lux (light intensity) to the plant. Tubular fluorescent bulbs are slightly cooler than CFLs. Remember that CFL bulbs lose lumen output over time—20-25% after 4000 hours. You should replace CFLs used as grow lights once a year.
rina_Ontario,Canada 5a
Original Author
4 years ago
mindshift

Some plants are more sensitive, and I have scorched some years ago when first used. I put etiolated plant very close - not touching, but maybe 2cm - to CFL suddenly, and it got scorched within hours...that was back in 2013, here is photo:

Good I noticed and pulled it away - it survived, regrew, and I still have it :) IMO, it is good idea to acclimatize plant to sudden light, even from LED.

I am not buying more CFL bulbs, but using up more than 40 I got for free. If I need new lights, I get LED now. I do not use any incandescent bulbs, they are much more expensive to use and do not last very long...

How close to light?

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Rob Blomquist

rina_Ontario,Canada 5a
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How close to light?

Comments (4)

Rob Blomquist

rina_Ontario,Canada 5aOriginal Author

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mindshift

rina_Ontario,Canada 5aOriginal Author

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rina_Ontario,Canada 5a
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rina_Ontario,Canada 5a
Original Author