A light roast usually presents less dominant dark-roast character and can make a coffee's fruit-like or floral impressions more noticeable. The source connects this style with the first cracking stage of roasting and a comparatively dry bean surface. Exact color and development still vary between coffees and roasters.
Buying light-roasted coffee does not guarantee a particular flavor, and the label alone is not a sound basis for a health claim or a precise caffeine comparison. Focus instead on the roaster's description and the drink you plan to make.
Light-roasted beans can be used for espresso as well as filter brewing. What changes is the recipe and the balance you may prefer, rather than a rule that one roast belongs to only one machine. Measure dose and output, record the grind setting, and adjust one variable at a time. If you are accustomed to a very dark espresso, expect the flavor to be different before deciding that the new coffee is incorrectly prepared.
The conversation
A good question can make a better brew.