Fig. 3 shows a freehand sketch of a desk lamp. The sketch uses thick and thin lines. The product is manufactured in large quantities using industrial proces...

(a) Thick lines on the outer shape of the sketch are used to show the outline and visible edges of the product, making the overall shape stand out clearly [1]. By drawing the silhouette and main edges in a heavier line weight, the designer ensures that the form of the desk lamp is immediately recognisable and visually dominant on the page, separating it from the background and from lighter detail lines.

(b) Thin lines are used for the dimension lines and the detail of the bulb so that they do not compete visually with the main outline of the product [1]. Dimension lines, annotations, and internal details are secondary information. If they were drawn at the same weight as the outline, the sketch would appear cluttered and the overall shape would be harder to read. The contrast between thick and thin lines creates a clear visual hierarchy: form first, detail second.

(c) One reason why freehand sketching is used in the early stages of a design process is that it is quick and allows ideas to be recorded rapidly without the need for drawing equipment such as rulers, set squares, or a CAD workstation [1]. The designer can explore many different concepts in a short time, capturing initial thoughts before they are lost and communicating them to others for early feedback. Speed is more important than precision at this stage, because most ideas will be refined or discarded before detailed drawing begins.