How about metallic spraypaint for reflection?

[ilovekasey17]

I built a grow box about 3 days ago. I was going to paint the inside white. However, my brain hatched a different possible idea. What if I spray painted the inside of the box with a metallic (aluminum color) color based paint? Has anyone done this? Would it reflect better than the white?

 

[TeaTreeOil]

Depending on the white paint the visible reflectance is anywhere from well under 50% to nearly 90%.

Aluminum is 90%.

I don't care what form of aluminum. Foil, sheet, micrometer coatings. It's all 90-95%.

Aluminum also reflects radiant heat(IR) at 95%. So some people will warn you about building 'ovens' with aluminum & HID.

It also has about 80% UV reflection.

Those are all averages.

As for your question. I'd think metallic paint is better than matte paint, which is highly diffuse.

Reflectivity is the LAW of incident angle = reflectance angle. Aluminum and shiny, smooth, metallic surfaces do this directly(mirror finish). Diffuse surfaces uniformly spread the light over ~180 degrees(Lambertian reflectance).

For instace, 40,000 lumens according to Lambertian reflectance distributes about 277 lumens/angle. While aluminum(specular reflectivity) would redistribute 36,000 lumens.

 

[ilovekasey17]

Depending on the white paint the visible reflectance is anywhere from well under 50% to nearly 90%.

Aluminum is 90%.

I don't care what form of aluminum. Foil, sheet, micrometer coatings. It's all 90-95%.

Aluminum also reflects radiant heat(IR) at 95%. So some people will warn you about building 'ovens' with aluminum & HID.

It also has about 80% UV reflection.

Those are all averages.

As for your question. I'd think metallic paint is better than matte paint, which is highly diffuse.

Reflectivity is the LAW of incident angle = reflectance angle. Aluminum and shiny, smooth, metallic surfaces do this directly(mirror finish). Diffuse surfaces uniformly spread the light over ~180 degrees(Lambertian reflectance).

For instace, 40,000 lumens according to Lambertian reflectance distributes about 277 lumens/angle. While aluminum(specular reflectivity) would redistribute 36,000 lumens.

Thanks. I'll try the metallic paint. I'm using CFLs so heat isn't a huge problem.

 

[ejf1676]

ive tried this and it works ok smoothing the surface before painting makes it way shinier? anyway i used it on louan over top of flat white and its reflective but very "diffuse" if paint is your only option white is probably as good as metallic in the real world thats my opinion from experience in the end i bought used mylar and it was as much as the paint hope that helps

 

[AeroKing]

For instace, 40,000 lumens according to Lambertian reflectance distributes about 277 lumens/angle. While aluminum(specular reflectivity) would redistribute 36,000 lumens.

So you're belief is that the plant can make better use of this pinpoint high intensity reflection than a distributed reflection?

I've always theorized that a plant can make better use of overall light when it is distributed throughout as much leaf surface area as possible - allowing the photosynthetic reactions to take place all over the plant (rather than one part of the plant doing most of the work, then having to transport all of the sugars... to the rest of the plant.

 

[TeaTreeOil]

The reflective surface changes the problem significantly.

Here's some very interesting lecture notes on the subject: http://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/DRAPER2/L02.pdf

Basically you're not getting anywhere near the intensity or quality of light with white paint as you do with a mirror finish metal like aluminum.

 

[AeroKing]

So, what do you think? Do you think that the plants will be able to use the pinpoint light better than the distributed light?

 

[TeaTreeOil]

I think directing the most photons directly as possible rather than having them bounce randomly in every direction would be the better environment for vigorous growth.