Glass heat shield blocks UV?

[franS]

I'm using a 70w HPS in the center of my cab (26" x 26" x 14") with a 23w blue cfl on each side. The HPS already has a tempered glass shield on the ballast that it came with. I want to add another sheet of glass, 1/8" thick, the same length and width as my cab, below all of the lights, to separate the heat from the plant. How will this extra glass affect the light getting to the plant?

My plant is still a seedling (6 days old), and I tried using the extra glass for a day and it
seemed to stop growth during that period so I removed it. I'm thinking that the UV rays
were getting blocked and thats why it stopped growing. Now, after removing it for a
day it seems to be back growing at the same rate as before the glass was installed.

Without the glass, temps are between 85F-90F. With the glass, temps are between 79F-
84F. So you can see my need for the glass, except the plant seems to be
responding better without it.

I'm assuming its better to judge by how the plant is growing, regardless of the high temps, than to just assume that it would be better with the glass because the temps are lower.

Am I right or wrong about this? Any advice?

Thanks

[johnnyutah]

I would add that sheet of glass back and just wait a little longer. Your temps look right where they should be.

They have special glass that is clear and blocks harmful UV rays but its unlikely
you got your hands on a sheet of that type.

[franS]

Thanks for the advice. The glass I'm using is from an old picture frame, so its not anything special, but I've been told that most glass will block the UV rays that are beneficial to the plant. Thats the only reason I took it out. I'd rather keep it in, but I don't want it to stunt my seedling if its blocking out beneficial light.

When you said my temps are where they should be, did you mean with or without the glass? Is 85F-90F too hot?

Thanks

[BrazyJay]

85 is really the max.... also u shouldnt need a glass cover for a 70w hps... get some better ventilation, your plants need it. even a fan blowing toward the bulb will likely reduce temps. and yes i have also heard that glass blocks beneficial rays from lights to plants. no matter what kind of glass it is, it WILL reduce lumens and possibly other beneficial things.