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The graph above shows the measured transmission curve for a filter with a conversion value (V) of -132 mireds and a filter with a conversion value of -160 mireds. For details on the mireds unit, please see the Conversion Values tab.

Features

• Pass Blue Light and Attenuate Red Light
• Available in Ø12.5 mm, Ø25.0 mm, Ø2", and 2" Square Sizes
• Ø25.0 mm Size Also Available Pre-Mounted in an SM1-Threaded Lens Tube
• Use with Our Broadband or Stabilized Broadband Light Sources

These Color-Temperature-Balancing Colored Glass Filters are designed to increase the color temperature of broadband light sources by attenuating light on the red end of the visible and near-IR spectrum and transmitting light on the blue end. The amount of increase depends on the original color temperature of the source and the conversion value (V) of the filter. Filters with a more negative conversion value will increase the color temperature by a greater amount. We offer filters with conversion values of -132 mireds and -160 mireds. Given their conversion values, these filters are particularly useful in imaging applications for color correcting a tungsten light source to more closely match natural light. For an explanation of conversion values and the mireds unit, please see the Conversion Values tab.

Unmounted filters are available in Ø12.5 mm, Ø25.0 mm, Ø2", and 2" x 2" sizes. The Ø25.0 mm filters are also available pre-mounted inside SM1-threaded (1.035"-40) lens tubes, which are each engraved with the Item # and conversion value of the filter. For easy integration with our broadband stabilized light sources, the Ø25.0 mm size can be mounted in the filter holder included with each source, as shown in the photo at the top of the page. For storage of our Ø25.0 mm or 2" square filters, we offer the KT01 and KT03 storage boxes, sold below.

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The photo above shows light from an SLS201L 2796 K tungsten-halogen source with no filter installed. For a plot of the power output with and without a filter, please see the Conversion Values tab.

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The photo above shows light from an SLS201L 2796 K tungsten-halogen source with an FGT200 Ø25.0 mm filter installed. For a plot of the power output with and without a filter, please see the Conversion Values tab.

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Click to Download an Excel File of Raw Data
The graph above shows the measured spectum of the SLS201L light source with and without a -132 mired filter or -160 mired filter installed.

The color temperature of a light source can be expressed in mireds (micro reciprocal degrees), given by 10⁶ divided by the temperature in kelvin. For example, the color temperature of our SLS201L stabilized broadband light source is rated at 2796 K, which equates to 358 mireds. The SI unit of mireds is reciprocal megakelvin (MK^-1).

The filters on this page offer a negative conversion value, meaning that they will decrease the mireds color temperature of light and thus increase the color temperature in kelvin. The filtered color temperature of a source can be calculated from the formula below, where V is the conversion value of the filter in mireds, K₁ is the color temperature of the source in kelvin before the filter, and K₂ is the color temperature in kelvin after the filter.

The table above and on the right gives calculated values for the color temperature of a selection of our white-light sources after being filtered. For example, the color temperature of the SLS201L light source when used with our -132 mireds conversion value filters can be calculated by first solving for K₂, such that K₂ = (10⁶) / (V + 10⁶/K₁), and then by plugging in the initial color temperature (K₁ = 2796 K) and the conversion value (V = -132 mireds) to produce K₂ = 10⁶ / 226 = 4432 K. The graph to the right shows the measured power output curve for the SLS201L source with and without the -132 or -162 mired filters.