Photoelectric (optical) pyrometer application range: select the typical non-contact temperature range in °C over which photoelectric/brightness pyrometers are suitable in industrial practice.

Introduction / Context:
Photoelectric (brightness) pyrometers determine temperature from the spectral brightness of hot objects, typically comparing radiation at a specified wavelength to a calibrated source and using optics plus photodetectors. They are used where contact sensors fail due to temperature, moving targets, or contamination.

Given Data / Assumptions:

• Opaque targets with reasonably stable emissivity in the band of interest.
• Line-of-sight access and minimal intervening absorption.
• Industrial conditions with hot metals, furnaces, or glass streams.

Concept / Approach:
Brightness/optical pyrometers operate effectively at higher temperatures where thermal radiation is intense and visible/near-infrared detection is practical. A commonly cited usable span is about 800 to 2500 °C, covering many metallurgical and kiln processes. Below ~800 °C, emitted brightness becomes low for visible-band devices, and total-radiation or long-wavelength IR methods are preferred.

Step-by-Step Solution:

Verification / Alternative check:
Manufacturer datasheets for optical/brightness pyrometers list lower limits near 700–800 °C depending on optics and detector sensitivity.

Why Other Options Are Wrong:

Common Pitfalls:
Ignoring emissivity; even within range, a poor emissivity estimate can bias temperature significantly.

Final Answer:
800-2500