Max light levels. Cats, dens, cymb, oncidium and vandas

[bil]

Originally Posted by NYCorchidman

It really depends on what specific varieties you have.
To be on the safe side yet still getting the great result in both growth and blooming, oncidiums and dendrobiums should places where they get all morning sun, but protected from the afternoon sun.
Or, you can go the other way around. Keep them off the sun, but expose them to late afternoon sun.
Direct sun will scorch ondidiums and dendrobiums (again, some like nobiles will be fine under direct sun).

Other genera you mentioned, cattleyas, vandas, and cymbidiums GENERALLY speaking, will take direct sun as long as you water and mist them good enough and there is enough air movement.
Midday hot sun can still be a problem but not in just a day. They will gradually yellow. When you see the leaves yellow, but still see green cast, then you don't have to worry much as that yellowish green leaves usually bring the best flowering.
Once you see burn spots or too much yellow developing quickly, then you want some protection.

To save any hassel, it's best to out thin shade over them, or place them where tall trees can shade them in the middle of the day.

Yeah, I found that the full sun here is just a bit too strong, as two cat leaves were starting to sunburn. So I'm constructing a table for them where the midday sun is screened and reduced to about 50% but the morning and evening sun still gets in.

[orchidsamore]

One major correction to everyone's opinions. Sunlight is never the issue. Heat concentration on the leaves is the issue. Of course sun brings heat so most people talk in maximum light levels. Including me.

But if you think heat CONCENTRATION rather than sun you may have less trouble deciding where to place your orchids.

I use the word concentration because 100-110 degrees is not the problem. Sunlight directly on leaves can raise the surface temperature of the leaf to 130-150 degrees. That will kill the chlorophyll in the leaves and we call that burn.

Now the other side is that if you have cool breezes, dappled light (moving leaves is an example), etc you can expose the orchid to more sunlight. Morning sun is not as hot as mid-afternoon sun, so most orchids will take up to full sun in the morning. The ground is cool. you house is cool everything helps to prevent heat buildup.

Flat leaves like Cattleya can catch and concentrate the heat. Terrete leaves (pencil shape) almost never burn, there is nothing to hold the heat. Bassovola leaves are pointed and point up. Heat rises and dissipates. Bassovola are hard to burn.

With no other conditions to reduce the heat here are some general numbers to start.

Family Foot candles
Cattleya 3500
Dendrobiums 2500-4500
Oncidiums 2000-3000
Phalaenopsis 1500
mounted Phalaenopsis leaves facing down 3-4000
Paphiopedilum 900
Zygopedilum 2500-3000
Vanda 4-8000
Grammatophyllum 3000-6000

The higher the light you give the orchid the better chance of flowering. So wherever possible place them in higher light wherever you can give them the conditions that will prevent heat buildup

[bil]

Originally Posted by orchidsamore

One major correction to everyone's opinions. Sunlight is never the issue. Heat concentration on the leaves is the issue. Of course sun brings heat so most people talk in maximum light levels. Including me.

But if you think heat CONCENTRATION rather than sun you may have less trouble deciding where to place your orchids.

I use the word concentration because 100-110 degrees is not the problem. Sunlight directly on leaves can raise the surface temperature of the leaf to 130-150 degrees. That will kill the chlorophyll in the leaves and we call that burn.

Now the other side is that if you have cool breezes, dappled light (moving leaves is an example), etc you can expose the orchid to more sunlight. Morning sun is not as hot as mid-afternoon sun, so most orchids will take up to full sun in the morning. The ground is cool. you house is cool everything helps to prevent heat buildup.

Flat leaves like Cattleya can catch and concentrate the heat. Terrete leaves (pencil shape) almost never burn, there is nothing to hold the heat. Bassovola leaves are pointed and point up. Heat rises and dissipates. Bassovola are hard to burn.

With no other conditions to reduce the heat here are some general numbers to start.

Family Foot candles
Cattleya 3500
Dendrobiums 2500-4500
Oncidiums 2000-3000
Phalaenopsis 1500
mounted Phalaenopsis leaves facing down 3-4000
Paphiopedilum 900
Zygopedilum 2500-3000
Vanda 4-8000
Grammatophyllum 3000-6000

The higher the light you give the orchid the better chance of flowering. So wherever possible place them in higher light wherever you can give them the conditions that will prevent heat buildup

Now that is a damn fine post. Thanks for that.

[NYCorchidman]

The thing is sun light is actually closely related to heat, so you cannot take the two apart in reality.

[orchidsamore]

One year my sales booth at the Redlands show was next to a pond with a spray fountain. It was very breezy that day and the cool air enabled me to put a table of low light plants (Oncidium, Zygopedium etc) in full Florida sun in June for the whole day.

I showed customers that if you felt the leaves they were always cool. If the breezes stopped the plants would be burnt in hours, but we keep them there from 8:00 AM to 5 PM closing.