I have a laser pointer but I have stopped using it in favor of using white LED. I think it shows much lighter tyndall than is possible with a laser..........Robb ----- Original Message ----- From: Matthew McCann PE To: silver-list@eskimo.com Sent: Saturday, November 22, 2003 12:20 PM Subject: CS>False Tyndall effect?
Hi, Ode! You asked, " Is there such a thing as a non conductive particle that's too small for visible light to reflect off of?" The answer is yes. A good example is water aerosol, that is to say, fog. Fog will scatter the shorter wavelengths in an automobile headlight, but will not scatter the long wavelengths in an amber-colored "fog" light. The TE that most CS users observe is scattered from the beam of a red laser diode with a wavelength in the range of 630 to 680 nanometers (6300 to 6800 angstroms.) A lot of valuable information is being lost when other visible wavelengths are overlooked. Green laser pointers are on the market. They are relatively expensive still, but coming down in price. Edmund Scientific Company recently dropped their price from around $350 to around $250. (This is still too expensive for me.) A less expensive alternative might be to make do-it-yourself TE sources at a variety of shorter but visible wavelengths, using ultra-bright LEDs and flashlight reflectors. Here is a list of some possible LEDs sold by Hosfelt Electronics. Orange LED, 2VDC@ 60mA, $3.49, 620 nanometers. Yellow LED, 1.9-2.5 VDC@ 20mA, $3.49, 590 nanometers. Green LED, 3.2VDC@ 20mA, $1.99, 525 nanometers. Blue LED, 2.5-3VDC@ 20mA, $0.99, 466 nanometers. Violet LED, 3.6-4VDC@ 20mA, $2.25, 420 nanometers. Ultraviolet LED, 3.7-4VDC@ 20mA, $2.25, 395 nanometers. The latter LED has some visible emission. Use it only if you know what you are doing! Its UV can damage eyes without it being apparent or immediately painful. Best regards, Matthew
