I guess you don't need Metal Halides to enjoy clams:
"Because T. squamosa is adapted to depths of 10 to 15 meters (32 to 48 feet), it requires less intense lighting. In my experience, although it is possible to successfully maintain this species using strong metal halide lamps for long periods of time, it does not seem to be the best environment for them. If the clam has a colorful mantle it can be placed under medium to strong lighting ââ"šÂ¬Ã¢â‚¬Â even if it exhibits iridescent blue or green colors, it probably originated in shallow waters where it received very intense light. Generally, T. squamosa can be successfully maitained using fluorescent lamps (four to six), and will even grow to large sizes under this type of illumination. This is definitely not the case with the smaller T. crocea, which is found in the most shallow reef zone in nature.
If the light intensity is not sufficient, the gold, green or blue patterns will quickly disappear and the mantle of the clam will be dominated by a brown coloration. Under extremely insufficient illumination, T. squamosa will develop an uneven brown coloration with darker and brighter areas on the syphonal mantle (Knop 1996). The brown color will get more intense in those areas of the mantle that receive the highest light concentration (due to an increase of zooxanthellae density), and the parts of the mantle that receive the lowest light intensity (e.g., shaded parts of the mantle) will bleach (due to a lower density of zooxanthellae).
If the clam comes from a hatcher, the situation may be different, because those clams are normally kept in shallow waters ââ"šÂ¬Ã¢â‚¬Â 2 to 4 meters (6Ã"šÃ‚½ to 13 feet) in depth. This is necessary in hatcheries to be able to have good access to the clams to control algal overgrowth or predation. Thus, these clams are adapted to stronger illumination than wild T. squamosa and can therefore be placed under metal halide lamps as long as they exhibit a bright luminescent color patterning with gold, blue or green, indicating they are used to bright illumination.
When a T. squamosa clam is purchased at an aquarium store and newly introduced to a tank, it is important to assure that it will not suffer from a sudden and excessive increase of illumination. In some cases the stocking conditions during transport and in the pet store donââ"šÂ¬Ã¢"žÂ¢t provide sufficient illumination, so the clam doesnââ"šÂ¬Ã¢"žÂ¢t have an opportunity to maintain its adaptation to high light intensities. In these cases, the luminescent golden, green or blue patternings are reduced and the mantle is dominated by brown coloration. Those clams must be acclimated to the strong halide lamps slowly.
Spectral composition of light
Because this clam is found at depts of 10 to 15 meters in nature, it does not receive the full spectral composition of sunlight. Therefore, T. squamosa can be kept under lamps with higher Kelvin (K) ratings like 10,000. But, again, you must determine whether it is a wild-caught clam or a clam raised in a hatchery. Generally, hatchery-raised clams are easier to adapt to the aquarium environment because they come from stable environmental conditions, whereas conditions in the habitat of wild-caught specimen may vary greatly."
-Daniel Knop
"Because T. squamosa is adapted to depths of 10 to 15 meters (32 to 48 feet), it requires less intense lighting. In my experience, although it is possible to successfully maintain this species using strong metal halide lamps for long periods of time, it does not seem to be the best environment for them. If the clam has a colorful mantle it can be placed under medium to strong lighting ââ"šÂ¬Ã¢â‚¬Â even if it exhibits iridescent blue or green colors, it probably originated in shallow waters where it received very intense light. Generally, T. squamosa can be successfully maitained using fluorescent lamps (four to six), and will even grow to large sizes under this type of illumination. This is definitely not the case with the smaller T. crocea, which is found in the most shallow reef zone in nature.
If the light intensity is not sufficient, the gold, green or blue patterns will quickly disappear and the mantle of the clam will be dominated by a brown coloration. Under extremely insufficient illumination, T. squamosa will develop an uneven brown coloration with darker and brighter areas on the syphonal mantle (Knop 1996). The brown color will get more intense in those areas of the mantle that receive the highest light concentration (due to an increase of zooxanthellae density), and the parts of the mantle that receive the lowest light intensity (e.g., shaded parts of the mantle) will bleach (due to a lower density of zooxanthellae).
If the clam comes from a hatcher, the situation may be different, because those clams are normally kept in shallow waters ââ"šÂ¬Ã¢â‚¬Â 2 to 4 meters (6Ã"šÃ‚½ to 13 feet) in depth. This is necessary in hatcheries to be able to have good access to the clams to control algal overgrowth or predation. Thus, these clams are adapted to stronger illumination than wild T. squamosa and can therefore be placed under metal halide lamps as long as they exhibit a bright luminescent color patterning with gold, blue or green, indicating they are used to bright illumination.
When a T. squamosa clam is purchased at an aquarium store and newly introduced to a tank, it is important to assure that it will not suffer from a sudden and excessive increase of illumination. In some cases the stocking conditions during transport and in the pet store donââ"šÂ¬Ã¢"žÂ¢t provide sufficient illumination, so the clam doesnââ"šÂ¬Ã¢"žÂ¢t have an opportunity to maintain its adaptation to high light intensities. In these cases, the luminescent golden, green or blue patternings are reduced and the mantle is dominated by brown coloration. Those clams must be acclimated to the strong halide lamps slowly.
Spectral composition of light
Because this clam is found at depts of 10 to 15 meters in nature, it does not receive the full spectral composition of sunlight. Therefore, T. squamosa can be kept under lamps with higher Kelvin (K) ratings like 10,000. But, again, you must determine whether it is a wild-caught clam or a clam raised in a hatchery. Generally, hatchery-raised clams are easier to adapt to the aquarium environment because they come from stable environmental conditions, whereas conditions in the habitat of wild-caught specimen may vary greatly."
-Daniel Knop