Introduction

Horizontal Integrating spheres can easily measure the diffuse reflectance and transmittance of the samples with uneven or irregularly shapes by positioning the samples horizontally. It allows precise measurement and increases the operating efficiency even for amorphous samples and samples that cannot be oriented vertically.

This article demonstrates how the horizontal integrating sphere can be used to obtain diffuse transmittance measurements of a contact lens.

V-750 UV/Vis spectrophotometer

Experimental

One of the typical  methods for measuring the absorption of a contact lens with a vertical integrating sphere is to sandwich the sample in a saline solution between two quartz plates, as shown in Figure 1. Using this method, air bubbles in the cell and deformation of the lens may prevent precise measurement of the sample and the vertical placement of the sample makes it more difficult to determine the measurement area.  Additionally, hard contact lenses may crack or be damaged when placed between the two quartz plates.

Figure 1. Contact lens sandwiched between two quartz plates

The horizontal integrating sphere allows samples to be placed horizontally in the sample holder as shown in Figure 2. The contact lens is held in an appropriate solution in the quartz cell during measurement. The net transmittance of the sample can be obtained by measuring a blank, or the lens holder filled with the preservative solution without contact lens. This blank measurement corrects for any stray light reflected from the surfaces of the sample holder and lens solution.

Figure 2. Dedicated sample holder for contact lenses

Figure 3 illustrates how the sample is placed on the sample holder and integrating sphere.

Figure 3. Sample placed on sample holder on the horizontal integrating sphere

Results

The contact lens transmittance spectrum is shown in Figure 4.

Figure 4. Transmittance spectrum of a contact lens

The horizontal integrating sphere is ideal for samples that cannot be measured with vertical placement. This accessory offers easy measurements for small or amorphous samples as well as samples that cannot be set vertically. Since the sample is placed on the top of the accessory, it can be measured while avoiding sample damage and also provide precise sample measurement of sample areas by simple visual examination of the specific area to be measured.