NALMCO Certified Apprentice Lighting Technician (CALT) Practice Exam

If you light an object using an LPS lamp, what color will the object appear?

1. Gray, black or yellow

2. Reddish-yellow

3. Bluish-white

4. Bright white

The correct answer is: Gray, black or yellow

When illuminating an object with a Low-Pressure Sodium (LPS) lamp, the light produced is predominantly in the reddish-yellow spectrum. This type of lamp emits light primarily in a narrow band around the yellow part of the spectrum, which can significantly influence the perceived color of objects being illuminated. As a result, when objects are lit under this type of lighting, they typically take on shades of gray, black, or yellow, as the narrow wavelength of light does not provide a broad spectrum for color rendering. Most colors do not reflect well under the monochromatic yellow light, leading many objects to appear in the shades mentioned. The other options, which suggest colors such as bluish-white or bright white, do not align with the characteristics of LPS lamps. Such lamps are specifically known for their stark yellow hue, which prevents the accurate or vibrant display of colors that would occur under more balanced or full-spectrum light sources.