My suggestion is to use a different type of light pattern for rock lights.
The lights you showed are "driving" lights, which present a very narrow intense light designed for long distance driving. You will get more usable light from a flood light pattern, which disburses intense light in all directions for a short distance - more effective for lighting your immediate surroundings. Unfortunately, it is rare to find low-price flood lights, as it's not as popular for "retail" stores.
One exception is the Hella 4" round, rubber housing flood light - usually available for under $20.00 each...
The lights you showed are "driving" lights, which present a very narrow intense light designed for long distance driving. You will get more usable light from a flood light pattern, which disburses intense light in all directions for a short distance - more effective for lighting your immediate surroundings. Unfortunately, it is rare to find low-price flood lights, as it's not as popular for "retail" stores.
One exception is the Hella 4" round, rubber housing flood light - usually available for under $20.00 each...