1. Measure the total power of the light emitted by an incandescent lamp.
2. Measure the irradiance of a screen due to light produced by a real light source.
3. Observe vignetting.
4. Make and characterize a quasi-Lambertian light source.
Radiometry is a subfield of optical science dealing with methods to measure optical radiant energy. In short, radiometry deals with measurements of radiometric quantities such as radiant energy and radiant flux. The most widely used radiometric quantities and their definition are shown in Table 2 A.1, fully reproduced in this chapter.
In many practical cases, the sensitivity of the human eye should be taken into account. This can be done by considering the area of photometry. The relationships between basic radiometric and photometric units are shown in Table 2 A.1.
This chapter focuses on measurements of radiometric quantities using the simple optical detector described in Chapter 4. After completing the experimental tasks in this chapter, you will appreciate the art and science of optical radiometry and its importance to numerous applications, including the booming field of light-illuminating systems.
Radiant flux: 1 W (watt) = 683.0 lm at 555 nm
1 J (joule) = 1 W s (watt second) Luminous flux: 1 lm (lumen) = 1.464 × 10−3 W at 555 nm = 1/(4π) cd (candela) (only if isotropic) 1 lm s (lumen second) = 1 talbot (T) = 1.464 × 10−3 J at 555 nm
Wear gloves to handle optical elements (lenses).
If you have not already done so, design an electrical circuit as shown in Fig. 13.1 to make a linear light detector (see Chapter 4 for more details).
- Optical table or optical rail
- Light sources (red cw laser, tungsten bulb)
- Object (arrow or cross)
- Mechanical holders
- Screws and screwdrivers
- Calipers and/or spherometer
- Squared graph paper
- Screen and screen with a hole
- Concave and convex spherical mirrors
- Thin and thick lenses: plano-convex, convex-convex, plano-concave
- Diaphragm (a simple opening made of paper may suffice) and adhesive tape to fix the diaphragm to a holder
- Hartmann screen
- Test reticle-grid