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OK... I recently got a turtle that requires UV; doing some research on how to best provide that UV has gotten me thinking about the lights on my planted tanks.

What I learnt when looking at UV lights was that it is essential not to have anything between the light and the turtle as pretty much all tank covers, from glass to mesh reduce the amount of UV reaching the turtle, in some cases down to almost zero.

So that has me thinking... If a glass tank lid reduces the passage of UV light to almost zero, does it also affect other wavelengths? What impact could that be having on the amount / intensity / wavelengths of light reaching my plants?

G_T

Never be afraid to try something new. Remember that a lone amateur built the Ark. A large group of professionals built the Titanic.

Unless it's tinted, it obviously doesn't have any effect on visible light wavelengths. I believe glass pretty much just blocks UV light (my technologist friend points out it doesn't block infrared). Also, it's desirable to have glass between the water and light fixture to prevent humidity and splash water from damaging the lights.

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I have read several books over the years some better than others, but they all had one thing in common when referring to lighting. That being that yes any kind of cover on the tank reduces the amount of light that reaches the gravel. Even the water itself will reduce the light. Light is lost from several factors, being reflections from the water, bleed off out of the sides of the tank, and the depth of the water reducing the effectiveness of the lights so that the deeper the tank the more light is required to reach the bottom of the tanks. Particulate in the water will also reduce the amount of light that reaches the bottom as well.

Some glass has a special UV blocking layer added into it on purpose, all though this type is what you get if you have the glass lids cut at a Hardware Store. So there is a trade off with lids and lighting, lids cut down on water loss but increase the amount of light that you lose.

Hope this helps GT

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Will I can tell you this that the glass sleeve in UV sterilizers is call crystal glass and is very thin. Look for a good repitle bulb.... they are exactly what you need. I can see the glass block the UV but the screen top would only block the uv rays partly and only until the UV coating on the screen fades away. Yes it has a UV coating on it.... all screens do......just the way they are made

Djrichie
"So Long, and Thanks For All The Fish" Douglas Adams

Hi,
Jim is correct with his comments about the glass. I've
read, and that was ages ago, that the glass used for
aquarium tops, does not appreciably affect the amount of
light that enters the aquarium. That being said, if you
went to a store that sells glass and had them cut a piece
to size then you have to be careful and specify what the
glass is being used for. Many of today's glasses are
designed to repel the UV light and admit only specific
frequencies of light.
As far as the screens are concerned, the industry is now
aware that anything exposed to the sun is subject to its
UV rays. The sun's rays fades paint, makes plastics
brittle, rots rope, and can turn tight window screens into
a delicate mesh that will fall apart.
Living at 10,000 feet elevation, I've found that I needed
to specify that altitude when purchasing paint, and
screening. When working on antennas I have to use special
UV resistant plastics for cable ties, and wire insulation.

As far as the UV light for reptiles is concerned, it is
nothing more than a "special light bulb" or fluorescent bulb
and is designed for the reptile to get right frequency
light for warming and to synthesize vitamin D and others
for its health.
The ones we use in a UV filter are far different and are
designed to kill.

Frank

-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

So...the general consensus is that, for the purposes of my planted aquariums (not the turtle), the need to protect the lights with glass, perspex, screen etc outweighs what little impact, if any, there might be on the passage of the required wavelengths of light to the plants.

Thanks for the replies folks.

G_T

Never be afraid to try something new. Remember that a lone amateur built the Ark. A large group of professionals built the Titanic.