Shade

[gonewild]

How to calculate the percentage of shade?

If a greenhouse roof has a 50% shade factor and a lower shade cloth of 50% is placed under it what is the resulting percent of shade?
Does logic apply?

 

[jeremyinsf]

Half and then half = 25% of original light, 75% shade.

 

[gonewild]

If the roof is 45% what % shadecloth underneath is required to get 90% shade?

 

[jeremyinsf]

80% shade cloth will get you close.

 

[gonewild]

80% shade cloth will get you close.

:clap:

 

[AdamD]

It depends on what time of day, what time of year, the pitch of the greenhouse roof, etc... Many factors come in to play. Have you tried a light meter? That is what ulimately helped me achieve the light levels I wanted, then from there I let the leaves be my guide.

 

[gonewild]

It depends on what time of day, what time of year, the pitch of the greenhouse roof, etc... Many factors come in to play. Have you tried a light meter? That is what ulimately helped me achieve the light levels I wanted, then from there I let the leaves be my guide.

No don't need a meter, once the shade is up I can tell by how it feels. I just want to know what % shade cloth to put under 45% acrylic panels and wind up with about 90% shade. So I was checking the math.

Confused my brain.
Like if you have two layers that are each 50% why that is not 100% shade!
Or if you have a 40% roof and add a 60% shade under it is it the same shade as if you have 60% roof with a 40% shade under it? :rollhappy:

Or does it make a difference in the % of shade depending on how far apart the layers are?......Does it?

 

[jeremyinsf]

There are a lot of other factors that also come into play - like, how dirty is the roof? It might be rated at 45%. But when it's dirty, it's not going to let as much light through. Older shade cloth might also accumulate dirt/dust, etc and let less through.

Happy to help with the math - just make sure you are considering the bigger picture!

 

[ALToronto]

If you have two layers of 50% cloth sufficiently far apart that the second layer gets all the light that passes through the first layer, then you have 0.5 x 0.5 = 25% light or 75% shade.

If you have the layers too close together, then you can end up blocking too much light when the solid material from the second layer ends up right over the clear spots of the first layer.

The answer to your second question is yes, it's the same. 0.6 x 0.4 = 0.4 x 0.6. At least in theory. If you look at the numbers in terms of light rather than shade, the calculations will make much more sense.