or the light gives the coin and unnatural color
If this is the case, then it's probably just adjusting your white balance. What is your camera make and model and have you looked at the manual for manually adjusting WB? The Janso lamps are preferred but far from a "must have" to take decent pictures. You can also try shooting outdoors in natural sunlight to compare the differences.
If it washes out the coin, you can also try diffusing the light a bit. Maybe wrap some kleenex around the cover. or shine through an empty milk jug.