Shade cloth! They use it in greenhouses to regulate light.

I agree with Declan J. Mccabe although I used a cheaper fix in my papers where we had to carefully control light intensity to limit photoreduction of metals:

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In that case we simply went and bought window screen and added layers as needed to decrease light intensity. What is super important is that you ensure your light source stays at the same distance as light intensity will decrease exponentially as you move it further away.

Using window screens which you can buy at any hardware store was really cheap and allowed us to exponentially decrease light intensity from a 200W bulb from an intensity of 200 umol photon m-2s-1 to 20 umol photo m-2s-1 (representative of deep waters where sunlight is attenuated). The nice thing is, it is also waterproof so it can sit in water although I would be wary of things growing in the screen that may contribute to additional shading if you are in a natural aquatic environment.

If you are looking to filter out UV, you will need to look for a material called Milar screen. We also used these to protect ourselves from UV lamps we use to sterilize but also assess how much UV light contributes to photo-catalytic processes.

If you have any more questions about primary productivity measurements I am happy to discuss things further. Post a picture here once you've finalized your setup!

Hope this helps,

Daniel

Hi Dr. Daniel Gregoire, how do you measure light shading capacity of the cloth that you used. Do you use quantum sensor to measure the light penetration on the layers of cloth? Thank you for responding to my inquiry.