Radiometry and Photometry Questions:

1

• Radiometry and Photometry Questions
• 1. IR radiation has longer wavelength than UV
• 2. IR radiation has a higher frequency than UV
• 3. IR radiation has more energy per photon than
  UV
• 4. About 1 of the light emitted by a 75 Watt
  bulb will enter an eye with a 4 mm pupil which is
  1 meter from the bulb.
• 5. If a 75 Watt bulb emits a total of 40xpi
  lumens, it will have an intensity of 40 lumens
  per steradian.
• 6. A surface, 2 meters from the above 75 W bulb
  has an illuminance of 2.5 lumens/m2.
• 7. This surface has a 50 reflectance, and thus
  will have a luminance of 1.25/pi cd/m2.
• Doubling the pupil diameter from 3 mm to 6 mm
  will approximately double the retinal
  illuminance.

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• Efficiency of light source
• lumens/watt (light output per unit of power
  input)
• Compare two household bulbs
• 75 Watt incandescent bulb lumens
• Efficiency lumens/watt
• 25 Watt Fluorescent bulb lumens
• Efficiency lumens/watt

How much illuminance is provided by such a
bulb?Recall Illuminance(lum/m2) Intensity/d2
(Inverse square law) Intensity (lum/sr)
total light output/4p Therefore 75W bulb at
1meter Illuminance total lumens/(4p x d2)
lum/ m2
________ lux
What is required lux for VA chart? Will a 75 Watt
bulb at 1 meter generate sufficient illuminance?
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Example questions on Radiation Hazard. 1.
Visible lasers are ideal for corneal
photocoagulation. 2. UVA radiation has shorter
wavelengths than UVC 3. Cataracts develop
earlier in regions with high levels of UV 4.
Solar Keratitis is a consequences of chronic
exposure to IR 5. Pterigium is caused by acute
exposure to UV 6. High intensity 193 nm lasers
can be used to perform trabeculotomies. 7.
Chronic exposure to high levels of IR can cause
cataracts. 8. BIO exposures should be kept
shorter than 10 seconds to avoid retinal
damage. 9. Laser pointers cannot be hazardous
because you can buy them at Walmart. 10. The
ANSI standard for ocular safety is based upon an
MPE which is equal to the radiation level likely
to generate a 50 probability of damage. 11.
The radiant output of class 3a lasers range from
1 to 5 Watts.
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National Board Exam A student who just took the
exam sat through Tuesdays lecture on
Radiometry/Photometry and confirmed that there
were at least four questions on this summers
exam covered by that material. Examples 1.
If retinal illuminance is 10 Trolands through a 2
mm diameter pupil, what is it through a 4 mm
diameter pupil, 10,20,30,40,50? 2. If Vl is 1.0
and 0.5 at 555nm and 650 nm, respectively, what
is the luminance of a radiation source emitting 1
Watt/(sr. m2) at these two wavelengths, 680,
1020, 1360, 1.5, 2 cd/m2? 3. If a piece of paper
is illuminated by a point source of intensity 10
lumens/steradian, and is located 1 meter from the
source. Its illuminance will be 10, 1, 2, 5, or
20 lux when it is tilted by 60 degrees? 4. The
luminance of a matte gray card with a reflectance
of 0.5 will be 5, 10, 5/p, 10/ p, or 1 cd/m2 when
illuminated by 10 lux?