# CFL vertical or horizontal

Discussion in 'Lighting' started by SemiOrganic, Jul 6, 2011.

1. Hey what's up all. New member... not yet a grower still researching :-/

Anyhow. I thought I remember seeing once, not sure if on this site persay, that CFLs best output is when they are facing down over your grow. Thing is, 99% of CFL users always have their bulbs sideways, and sometimes not even with a reflective material... I understand that placing them vertically you lose a few inches of grow space, but if you had enough to spare wouldn't it be more beneficial to place them correctly?

Can someone prove if vertically/horizontally is the best way?

2. Well think of it in terms of surface area of the spiral of the bulb. If you look at a bulb holding it vertically above you, there really isn't that much area, but if you turn it to the side there is a bunch more surface area. And of course the more surface area you have, the brighter it is going to be.

3. Well yea it appears that way. Like I said though I think there is actual fact that proves pointing them down you get more light. Sideways you essentially lose the other surface half of the bulb... I just can't seem to find the proof that I had come across before

4. It doesn't appear that way, it is that way. If I placed a lux meter underneath a bulb just like where the plant sits and compared putting them vertically and horizontally the horizontal would give much more light.

And sure, you lose half of the bulb placing it sideways, but if you place it vertical you lose ALL of the sides. The only way a vertically hung bulb would be beneficial is if it was in between two different plants.

When a bunch of people do things a certain way, more often than not there is a good reason behind it.

5. ^I agree, the bulb gives off light across its surface area, so a spiral CFL hung horizontally above the plant presents more surface area of the bulb and thus should be giving more light to the plant. But, a CFL hung to the side of the plant should be hung vertically, for the same reason (now the side of the bulb will be facing the plant).

6. What about two cfl's in a splitter, both of them pointing diagonally down and out? I've seen this a lot in pics while researching.

Thoughts / Opinions ?

7. the most important aspect of using CFLs is using reflectors for them. Bar none. this reflects/redirects the light that would otherwise be "lost" in the direction that you want it to go. Which way the CFL is "pointing" really has little to no effect relative to the use of refelectors.

They produce a globe or halo of light, so basically no matter which way you hang it, 50% of the output is going to be directed away from the plants....unless you reflect it towards them.

8. #8
Last edited by a moderator: Jan 19, 2014
ignoring the led thing...if you want.....

CFL
Light Source Efficacy65lm/W 54% Fixture Efficacy35 lm/W
XLamp XR-E Neutral White
Light Source Efficacy58 lm/W 77% Fixture Efficacy44 lm/W
Figure 2: Comparison of CFL & LED Coefficient of Utilization.​
I believe that CFl's are not strong enough to get 100% out of your plant... but if you put them vertically with a good reflector, then you will be getting at least a decent 'hot spot' (lumen wise).. (see bottom of post) SO you get less space for more light intensity... if you use enough, it might be worth it to go vertical... right?

To calculate fixture loss for the CFL example, we assumed 85 percent reflectivity for the fixture reflector cup and that 60 percent of the light will hit the reflector cup. Therefore, the optical efficiency will be:

Optical Efficiency = (100% x 40%) + (85% x 60%)
Optical Efficiency = 91%

from
/www.digikey.com

Plus I found this...WOWOWOOWW

9. I heard that a fluorescent tube is brightest in the center. I dont know if this is true.

Assuming it is, a CFL center is the part pointing straight down.

I have read some saying the light coming from the center of your CFL is a little more powerful. But diminished quickly to the sides.
Horizontal placement has better coverage, with a tiny loss in brightest as you move from center.

So having them slightly angled with them over a plant and pointing down towards another, would utilize pros and cons of both positions.

10. Many rights and many wrongs here,understand how the bulb actually works will make you make the correct decision ...so go vertically to expose the most lumens to the foilage