Homework 2
(1) How many LED’s are in the large video screen at the Arizona Football Stadium?
HINT: See our notes for Lecture 5.
▪ We defined “pixel pitch” as the spacing between each pixel.
▪ For this problem, assume 3 LED’s per pixel (1 Red, 1 Green, and 1 Blue)
▪ There are 25.4mm per inch
(2) Consider a 100W incandescent tungsten light bulb. Assume that the temperature of the filament is 2500°C.
What is the wavelength where the light output from this bulb peaks (is maximum)?
HINT: Use the equation that we talked about in class: λ·T = 3000 (μm·K)
Quote your answer in nanometers.
(3) If you want to shift this peak output to a longer wavelength, what must happen to the temperature? Explain.
(4) In class, we saw the demo where I aimed red, green, and blue laser beams on the wall. For this problem, assume
that each laser emitted 5mW of optical power. Calculate the number of lumens in each beam.
HINT: Use the curve showing the response of the human eye to various wavelengths, on page L5-8.
λ(blue) = 405 nm ; λ(green) = 532 nm ; λ(red) = 650 nm
(For the following 2 problems–print out pg. 69 and use a ruler to draw rays on the figure to show your answer.)
(pdf scan)
(5) Problem P12 (on pg. 69).
(6) Problem P13 (on pg. 69).