'Desert' and 'terrarium' are mutually exclusive - you can't have a successful one with the other. Cacti and other succulents needs air flow and shouldn't be, for the most part, subjected to the humidity that a terrarium has. This growing environment is not suitable for the plants you have.

Those plants all want way, way more light than a 50W bulb will provide in addition to any ventilation/water problems you may have.

I've used a variety of Sansevieria in terrariums with great success (although they tend to look more tropical than desert-dwelling). They tolerate a huge range of light and water and some of the dwarf ones look really great. Other than the standards like Pothos and English Ivy, these are the only plants I can reliably keep alive in a terrarium long-term.

You could also look into Haworthia and Gasteria. Neither will do well long-term, but they will survive long enough to get your money's worth at which point you can toss them out, and put some fresh ones in.

No matter what you decide, I highly recommend putting the plants into pots, which then get put into the terrarium. You can bury the pots in the substrate if you like. Planting them directly into the substrate drastically increases the work involved in switching out plants, and prevents you from having a nice potting mix for the plant. Pots are pretty much necessary if you do go with Sansevieria to keep the plant from taking over the whole terrarium!

What would be an acceptable humidity level at 85F?

I'd forget the Haworthia & Gasteria too, they won't like humidity & are likely to rot.

Not sure why you're associating desert & terrarium, as McHarris states, these really do NOT go together.

Terrariums tend to do best w/ tropicals or semi-tropicals. I'd suggest you try that rather than any succulents.

I grow both, but only semi-tropicals in my terrariums.

Having had nearly two dozen terrariums full of all sorts of different animals in my apartment, I find these "terrariums are wet comments" shockingly ignorant. Just because your experience is limited to tropical or temperate terrariums, doesn't mean that is all there is.

Seriously, the plants are freaking decoration. There will never be enough water in a tank for a leopard gecko to rot a succulent. Sure, without proper light, air, etc, they will languish and die. But for $3 from Home-Depot, who cares if you have to replace them every year. Just get something slow growing that doesn't absolutely demand full-sun and it will certainly look better than putting plastic plants in, and you won't kill your gecko by trying to force it into the wrong environment...

Do *NOT* listen to anyone telling you to make a tropical tank for your leopard gecko, as that will certainly lead to disease and death. If you don't know what you are talking about, DON'T POST!

Sorry I should have been more specific. The front of the enclosure is all screen so there is plenty of ventilation. Humidity is not an issue. Also the plants are in a pot which is then put into substrate to make for easy cleaning and maintenance. My main concern is the lighting. I want to find a balance so that the plants are receiving enough light but the geckos aren't stressed from too much light.

I guess the question should be: what kind of lighting is suitable for growing succulents indoors?

Here is a picture

Jo,

You might pls. try calming down a bit. I DIDN'T SAY A SINGLE WORD ABOUT GECKOS, WAS ONLY TALKING ABOUT THE PLANTS.

You can take it from here, if you want to encourage someone in dying plants, go ahead.

Thanks for the picture, I think your terrarium already looks pretty good! I love seeing a sweet old-school TV cabinet being put back to work. The acrylic lip in front is a great idea to keep all the sand from draining out. Some pet stores (the kind that carry snakes and lizards) have decent looking "backgrounds" you can get to add a little depth to the scene and cover the square hole in the back of the TV, if you don't already have plans to decorate the interior.

As to your specific question, fluorescent lighting and HID lighting (like sodium or mercury arc lamps) are the only options for growing succulents indoors. Although they are cheap and easy to work with, fluorescents have very low intensity, and therefore must literally be mounted within inches of the plant to really work well. More than 12" away and it is almost useless...

HID systems are far more intense, and can allow you to mount the lamps a considerable distance from the plant and still get good results. Unfortunately the HID stuff is unlikely to work for your application since it's generally more complicated to work with and bulky (not to mention pricey). With enough determination you are clearly capable of getting either system working, but both approaches seem like they would sort of overwhelm your project. In the end it's the *whole thing* you want noticed, not just a couple succulents getting blasted with light! I think you are left looking for low-light plants that you can keep alive, or at least only kill slowly, or plastic.

If you want to skip the plants entirely, that would certainly be a natural setting for your gecko. You could go to a landscape supply yard a get a nice selection of rough, "dramatic" rocks and make a tiny bit of a rocky hillside inside your terrarium. Probably better to avoid using river rocks if you really want an authentic look; not a lot of rivers in that part of the world!

As for the gecko itself, whatever you do, be careful not to raise the substrate temperature too much. Being nocturnal, the gecko will just hideout during the day so the intensity of the light itself isn't really a danger for the gecko. However, light will heat the substrate and with a really high power lighting system, you could easily cook the poor little guy.

'You can take it from here, if you want to encourage someone in dying plants, go ahead.'

I'm green with envy that you said it first.

ok well basically it sounds like this idea isn't going to work. thanks for the help, though i could have done without all the arguing.