3) of light acceptance by detector- Centered at 90° to the incident light path and not to exceed t30° from 90°. The detector and filter s if used, shall have a spectral peak response between 400 and 600 nm. clear, colorless Sample cells. Use sample cells or tubes of ed glass or plastic. Keep cells scrupulously clean, both inside and out, and discard if scratched or Never handle them where the instrument's light beam will strike them. Use tubes with sufficient extra length, or with a protective case, so that they may be handled properly. Fill cells with samples and standards that have been agitated thoroughly and allow sufficient time for bubbles to escape. Clean sample cells by thorough washing with laboratory soap inside and out followed by multiple rinses with distilled or deionized water; let cells air dry. Handle sample cells only by the top to avoid dirt and fingerprints within the light path. Cells may be coated on the outside with a thin layer of silicone oil to mask minor imperfections and scratches that may contribute to stray light. Use silicone oil with the same refractive index as glass. Avoid excess oil because it may attract dirt and contaminate the sample compartment of the instrument. Using a soft, lint-free cloth, spread the oil uniformly and wipe off excess. The cell should appear to be nearly dry with little or no visible oil Because small differences between sample cells significantly impact measurement, use either matched pairs of cells or the same cell for both standardization and sample measurement