# Light meter



## Corbin (Feb 5, 2008)

If you are growing under florescent lights do you need a light meter? If so how do you use it since florescent lighting does not come close to the fc mentioned for growing orchids in natural sunlight? 

All help / suggestions will be appreciated


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## SlipperFan (Feb 5, 2008)

T8's are brighter than T12's. Fluorescent fixture ballasts can cause dimming of lights over time, as well as the aging of the tubes themselves. I just keep the plants about 3-5" under the lights, and make sure there are enough of them to light the whole plant, not just the tops.


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## rdlsreno (Feb 5, 2008)

I grow mine under lights so I use a light meter. I ranges from 800 to 2,500 FC. I use a 600 watts HID lights.

Ramon


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## Corbin (Feb 8, 2008)

SlipperFan said:


> T8's are brighter than T12's. Fluorescent fixture ballasts can cause dimming of lights over time, as well as the aging of the tubes themselves. I just keep the plants about 3-5" under the lights, and make sure there are enough of them to light the whole plant, not just the tops.



So you do not meter the light.


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## Rick (Feb 8, 2008)

I find a light meter helpful when growing under florescent lights.

You cant change the output of the bulb, but you can change the distance between the plant and the bulb, increase the number of bulbs, and add reflectors.

All of the above factors will change intensity considerably. They can also influence temperature considerably too.


Allot of times I've had to run the bulbs within a few inches of the plants to get the ft candles where I wanted them. But then you have to check temps to make sure you aren't cooking the plants.

Then you add fans to blow the heat away from the bulbs.


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## SlipperFan (Feb 8, 2008)

Corbin said:


> So you do not meter the light.


I have an incident light meter. I use it more for comparing light bulbs and their intensity using f/stops rather than footcandles. I'm used to thinking in f/stops because of my background in photography. I know there is a formula for converting into footcandles, but I don't use it.


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## Corbin (Feb 11, 2008)

Rick said:


> I find a light meter helpful when growing under florescent lights.
> 
> Allot of times I've had to run the bulbs within a few inches of the plants to get the ft candles where I wanted them.



So Rick, and I know it will vary depending on the species of the orchid, but what sort of reading do you look for?


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## Rick (Feb 11, 2008)

It definitely depends on species, but some groups are easier to generalize than others too.

Many of the barbata paphs will do fine at 800 to 1200fc. So will most phals and pleurothallids.

Many of the multifloral paphs (maybe sanderianum and parrishii the biggest exceptions) like from 2000 to 3000 fc. As will allot of Cattlaya.

Many Vandas can run up to 5000 fc. Especially the ones with terete leaves. 

Then there are many species that like seasonal differences from low to high.

Temp and humidity are also related to the equation. The more light the more heat when working in enclosed areas. So some of the higher elevation plants that may enjoy brighter light will suffer if you don't keep the temps down and humidity and airflow up. My wilhelminea and many of my phrags seem to fall in this category.

I was pretty amazed one time when I measured leaf surface temps on a plant in the GH in a bright spot. The air temp was reading about 85 but the leaf surface was close to 100. The plant was a roth with paler than normal leaf color. I then added the swamp cooler which boosted humidity and airflow to the corner of the GH where the plant is kept. The leaf color got darker green, and leaf length increased. Max leaf temp I've measured is closer to 90 now.


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## Rick (Feb 11, 2008)

It's also real hard to come up with hard and fast light level numbers when talking about a GH rather than artificial lights.

Light levels change all day long, and very with cloud cover. So when I talk about GH levels of light I usually shoot for a spot which will be consistent for about 3 or so hours a day at a given level.

Under lights you can supply a set amount of light for 16 hours straight, day in day out. So you can probably get away with 20% or so less under lights than in a GH


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## Corbin (Feb 12, 2008)

Thanks Rick


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