yes a 5% lamp of any kind would be next to useless in this type of setup. the mesh will half the power of the lamp anyway.
may i suggest our new UVFlood fitting. it is being used with great sucess by Cham keepers as it is very powerful 12% T5 Power compact but has avery special reflector as part of the kit that forces light and energy from light through the mesh. it lights a targeted area so that you can maintain a decent gradient in these tall narrow units and still provide good shade.
D3 UV Flood Lamp | Arcadia Reptile
the unit is totally waterproof and flicker free and can be obtained in some cases cheaper than a full size T5 system. In your set up i think it will be perfect!
John Courteney-Smith MRSB.
Arcadia Reptile; Head of Science and Innovation
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