Measuring Florescent light output

[Stray59]

Does anyone know a rule of thumb for measuring light output? Basically, what wattage do I use for cattleya culture, and what should I use for phalaenopsis or paphiopedilum? I know that distance from the bulbs also matter, so how far should they be from the source. Any info or link to a good instruction page would be appreciated!
Steve

[WhiteRabbit]

good luck!

[naoki]

Steve, my phals and paphs grow well with around 800-1000fc for 15 hours. They are in a grow tent, so they don't get any ambient light. At one point, I made a following calculation (I posted it to one of the forum, but I can't remember): the cumulative amount of photosynthetically active radiation (PAR) from this setup is roughly equivalent to that of natural sun light with 1200-1500fc of peak intensity (this kind of "peak intensity" is the type of values used for "recommendation"). I grow only species, so hybrid phals may do ok with less light.

If you are using T8 (32W for 4'), then you want to put them within 2-5 inches. If your grow space is about 1'x4', you probably want to have 4 bulbs (2 stoplights). If you are using T5HO (52W for 4'), then mine is about 7-10 inches from the top of the leaves.

In the summer time, I may need to put them further to prevent heat related problems.

I don't have much experiences with growing Cattleyas under lights, but my 3 rupicolous Laelias are growing well (they are still too small to flower) about 4 inches from T5HO (I think it's getting around 1600-1800 fc). I don't know if they will flower if you are using T8, and T5HO may be better. If you can put them outside during the summer, T8 may be enough for the winter.

I posted some measurement of a T5 fixture, but is it for 2' unit and not 4' unit:
Big Leaf Orchid forum • View topic - 2' 1 or 2 bulb T5 Fc question

[blackvine]

Steve, I struggled with this a few months ago when I first started growing orchids. Focusing on Catts, which need 3,000 - 5,000 footcandles, I found a simple "step down" chart, showing the decrease in footcandles by foot. Here it is:

Trend as we move in one-foot increments from the light on the ceiling to the floor in a normal house with eight-foot ceilings:
1 Ft = 500 Lm
2 Ft = 125 Lm (25% of 500)
3 Ft = 55.5 Lm (11% of 500)
4 Ft = 31.25 Lm (6% of 500)
5 Ft = 20 Lm (4% of 500)
6 Ft = 13.8 Lm
7 Ft = 10.2 Lm
8Ft = 7.8 Lm
By moving just seven feet further from the light source, the intensity of the light has decreased from 500 Lumens to less than eight Lumens.

All you need to know is how many footcandles your light puts out. This should be printed on the box. It may be stated in "lumens", but for all intents and purposes an FC is equal to a lumen. (A footcandle is a unit of measurement describing the intensity of light one foot from a candle).

From that starting point - your footcandles of light - decrease by the percentages I've shown in the above table. So if your light has 20,000 FCs, your Catt will recieve 6% of that if your light source is 4 feet away. I have lots more info, but I just use this chart because the math is mind boggling! If you want it, though, let me know.

[Ray]

Originally Posted by blackvine

So if your light has 20,000 FCs, your Catt will recieve 6% of that if your light source is 4 feet away. I have lots more info, but I just use this chart because the math is mind boggling! If you want it, though, let me know.

Actually, that figure would only hold true if the light output was 20,000 footcandles at 1 foot from the bulbs.

The drop off is an inverse square - twice the distance = 1/4th the intensity, 3x the distance, 1/9th, etc. That means that if the output is 20,000fc at 1" from the bulbs, it will be 5000 at 2", etc.

However, don't disregard the effect of reflectors, as they will redirect the "lost" light from the part of the bulb facing away from the plant, down toward it.

I did some measurements once, using a 2', 24W T5 fixture:

[Calbears]

Originally Posted by Ray

Actually, that figure would only hold true if the light output was 20,000 footcandles at 1 foot from the bulbs.

The drop off is an inverse square - twice the distance = 1/4th the intensity, 3x the distance, 1/9th, etc. That means that if the output is 20,000fc at 1" from the bulbs, it will be 5000 at 2", etc.

However, don't disregard the effect of reflectors, as they will redirect the "lost" light from the part of the bulb facing away from the plant, down toward it.

I did some measurements once, using a 2', 24W T5 fixture:

Ray, are the units on the graph correct? I'm thinking it should read feet not inches. I just can't believe all that light would fall off in one foot.

[naoki]

Originally Posted by Calbears

Ray, are the units on the graph correct? I'm thinking it should read feet not inches. I just can't believe all that light would fall off in one foot.

The unit on the graph is probably correct. Here is my measurement, which matches well with Ray's.

http://www.orchidboard.com/community...tml#post572079

[Discus]

Originally Posted by Calbears

Ray, are the units on the graph correct? I'm thinking it should read feet not inches. I just can't believe all that light would fall off in one foot.

Lighting reduces its intensity as an inverse square law, hence the (initially "illogically" fast) dropoff.

If you want to try and wrap your head around why, think about a cylinder of paper wrapped around the light at different distances out - the further away your cylinder is, the bigger the surface area gets - at a really quite rapid rate - yet the bulb is still only producing so much light, so it gets "spread" more and more thinly.

This is also why even really bright lights (like flash bulbs) do absolutely nothing in a stadium other than look pretty sparkling on the TV, and give the photographer a disappointing picture of the back of the heads of a few rows in front of them...

[Orchidflowerchild]

Originally Posted by Discus

This is also why even really bright lights (like flash bulbs) do absolutely nothing in a stadium other than look pretty sparkling on the TV, and give the photographer a disappointing picture of the back of the heads of a few rows in front of them...

And also why sitting plants "near a window" is not really likely to garner much success unless they are pretty well IN the window. Also why an office desk is a horrible place for a plant. Light is important to consider, but yo0u also have to consider direction of light, duration of light, intensity of light, and angle of light. I bloom Cattleyas under t-8 (anmd back in the day even T-12s!) but I do keep the leaves within 4" of the bulbs.

The human eye is pretty good at making dim lighting look brighter to our mind than it is.

-Ceci

[Stray59]

WOW - I can always count on Orchid Board members to come through! Whiterabbit, Naoki and blackvine to the rescue! I can really use all this info. I am currently using a blend of T12 (yes I know, almost useless, but it is what I have now), T8 and will soon be adding some T5's in the near future. In the past, the orchids I have had 'survived' in the lights I had, but now I need to move it up and get some blooms. Currently I have been able to bloom pescatoria under the lights I have, but have many Cattleyas, laelias, brassovola, etc. that I am moving out of the window sills and onto growth shelves. I also am deflasking seedlings for future stock / resale and need to make sure I am providing enough light for them to grow well. I will eventually have 4 distinct growing environments, each adjusted to the varieties that I grow. This is kind of a 'late in life' career attempt and hope all goes well with it. Keep your fingers crossed for me please!
Thanks to all of you for your input. I was basically housebound for 18 months due to a herniated disc and have focused on my orchids a lot. Currently I have about 125, all grown in window sills, of a wide variety of tribes.
Thanks for letting me blab on, but I want you to know you are really appreciated and the info you are sharing is truly assisting me in my new venture.
Have a great day, all of you -
Steve