Arc or Halogen Lamp?
Several important factors decide the best type and Total Output size of lamp for your application. How large is the area you are irradiating?
Spectral Distribution If the area you are irradiating is large, then in many cases total output is more important than radiance. What wavelength do you need? The radiance of a 75 W Xenon arc lamp is similar to that of a 1000 W Xenon arc, but if your target Which wavelengths will cause stray light or unwant- is an area of a few square cm, the 1000 W source ed sample heating? will produce about 30 times the irradiance of the smaller lamp. You should choose a lamp with high output in your spectral region and low output at wavelengths that In cases where you are using the raw lamp output, can cause stray light or other problems. Arc lamps and collimation is not important, the irradiance are primarily ultraviolet to visible light sources. curves are a good basis on which to choose the Mercury arc lamps have very strong peaks in the lamp. ultraviolet region.
Tungsten halogen lamps are a good choice for long- Source Size and Shape wave visible to near infrared applications. For typi- cal spectral data of these lamps go to the chapter What is the Target Shape and Size? „Lamp Spectra and Irradiance Data“ on www.lot-oriel.com/lightsources („Basics“). Available optics and the size and shape of the source determine how much you can get on target. An elongated source can be a better match to a slit Radiance target.
How bright do you need the image to be? With non imaging reflectors such as elliptical reflec- How large is the area you are irradiating? tors, the size, shape, and angle of the secondary image are more important than the primary arc or Usually between the source and the area to be il- filament. luminated (monochromator slit, fiber optic, detector, target) you‘ll find one or more lenses. With lenses or any kind of imaging you can change the irradiance Source Stability on the detecting area, but not the radiance. You can‘t get an image that is brighter than the source. How important is Spatial and Temporal Stability to your application? If you have to pass the radiation through optical components, then radiance is important. Smaller Spatial and temporal stability of source radiation sources are easier to collimate and therefore better is so important for some measurements that double to focus. If for example you would like to irradiate a beam design is standard. In general, tungsten halo- slit, fiber or pinhole i.e. if the area you are irradiat- gen lamps are more stable than high radiance arc ing is of the same size or smaller than the source, lamps. then the radiance of the wavelength you need is important. Optical Feedback can improve long-term source stability but it is also important to use good design The irradiance curves divided by source area give practice. For example, the convection currents inside a first order comparison. For example the radiance an arc lamp lead to a lot of fluctuations on the low produced by a 75 W Xe lamp is 2,7 times higher radiance outer regions of the arc. A well designed than the radiance of a 150 W Xe lamp because the system will not use these unstable zones. arc size is 8,8 times smaller. For values of luminance [cd/mm-2] go to the chapter „Arc Lamps, Specifica- tions“ on www.lot-oriel.com/lightsources („Arc Light Sources“).
1 Your Contact: Jochen Mentges, Phone: +49 6151 880635, E-mail: [email protected] LOT-Oriel Group Europe. Im Tiefen See 58. D-64293 Darmstadt. Fax: +49 6151 896667. www.lot-oriel.com Arc or Halogen Lamp?
Arc Lamps Halogen Lamps
Features Features l High radiance in the ultraviolet and visible. Mercury l High total visible output lamps have spectral lines of very high irradiance in the l Excellent stability ultraviolet l Excellent photometric or radiometric sources l High ultraviolet output (250 – 2500 nm) l Small concentrated arc l Slow variation of output with wavelength l Xenon lamps have spectral distribution resembling the sun
Benefits Benefits l Produce highest irradiance on small targets l Easy to use l Intense collimated beams because of small, high radi- l Simplify detection in spectral scanning ance source l Smaller priced than arc lamps l Excellent sources for UV photochemistry l Can simulate daylight
2 Your Contact: Jochen Mentges, Phone: +49 6151 880635, E-mail: [email protected] LOT-Oriel Group Europe. Im Tiefen See 58. D-64293 Darmstadt. Fax: +49 6151 896667. www.lot-oriel.com