Those are both incandescent bulbs, which means the produce heat/light by running electricity through a filament - you can see it glowing in the picture of the spot bulb.
The spot bulb has been coated so that the heat/light will be mostly directed in one direction. If you're putting a bulb above the tank or in a dome fixture, I would use a spot bulb rather than a standard incandescent - no point in radiating light where it isn't needed.
Spot bulbs can be had in other styles like fluorescent and halogen.
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