no light filter

[Dusky Batfish]

Just curious if there are any good or bad effects if there is no glass or acrylic between a light fixture and the aquarium water?

[FoMoCo Master Tech]

Are you talking about a cover on the lights or a cover on the top of the tank? Covers for the light fixture are a good thing as they protect the components. You do lose some light intensity but it should be minimal.

Putting covers over the tanks opening is a different story. The loss of light intensity would likely be greater due to water droplets forming on the cover and eventually an algae film would develop so it would have to be cleaned regularly.
More importantly, a cover over the tank opening would greatly reduce beneficial gas exchange between ambient air and the water's surface. It could also contribute to the water's heat build up due to the reduced evaporation.
My light fixture came with an acrylic shield to protect the bulbs, reflectors and wiring but it didn't fit so I didn't use it. If it fit right, I would have used it.
My tank came with acrylic covers for the openings but I never used them for the above reasons. If you're concerned about fish jumping out of the tank ( which some fish tend to do), you can always put plastic egg crate over the opening(s) to prevent that.

[Dusky Batfish]

Okay thanks a bunch. I was more wondering about like burning the tank critters almost like a tanning bed when used for to long. So the only problems are usually eventually to little light if a cover gets build up. So an open top tank is better as long as there isnt to much un-monitored evaporation?

[FoMoCo Master Tech]

Okay thanks a bunch. I was more wondering about like burning the tank critters almost like a tanning bed when used for to long. So the only problems are usually eventually to little light if a cover gets build up. So an open top tank is better as long as there isnt to much un-monitored evaporation?

As long as evaporated water is constantly replentished with H2O ( not saltwater ), its better to have an open top. It promotes gas exchange and keeps the water cooler ( through evaporation). If you're not on top of replacing the evaporated water, you'll have salinity swings and related chemistry issues.