Illuminating unit

An illuminating unit for illuminating an imaging range of a monochromatic camera mounted on a board work machine for working on a board, comprising:

• a red light source configured to emit a red light;
• a green light source configured to emit a green light;
• a blue light source configured to emit a blue light;
• and
• a lighting controller configured to adjust independently respective light amounts of the red light source, the green light source, and the blue light source, wherein
• a first target light amount of only one of the red light source, the green light source, and the blue light source is multiplied by a dimming coefficient a to obtain a first dimming range,
• a second target light amount of only one of the red light source, the green light source, and the blue light source is multiplied by a dimming coefficient β to obtain a second dimming range,
• a target light amount of only one of the red light source, the green light source, and the blue light source is multiplied by a dimming coefficient γ to obtain a third dimming range,
• α<γ and β<γ, and
• the lighting controller adjusts the respective light amounts of the red light source, the green light source, and the blue light source a same number of graduations within the first dimming range, the second dimming range, and the third dimming range.