Student Help: Convert mW/cm2 to nm

Shorter wavelength light as more energy per photon (or wave cycle, looking at it that way). However, mW/cm² depends even more on the amount of incident light, so the two measurements are not one-to-one related.

You are confused as to what the meter measures. It only measures brightness or intensity of the UV light hitting it. It does not measure wavelength, or "color" of the light hitting it. The General Tools light meter that you have measures the intensity over a broad range from 280 nm to 400 nm.

To measure wavelength, you need a spectrometer.

I would send it back and get a refund.....and buy something like this....

http://www.amazon.com/Portable-Checker-Atmospheric-Light-Meter/dp/B00481APE8

...and let her build something like this....

http://coolcosmos.ipac.caltech.edu/cosmic_games/spectra/makeGrating.htm

No cigar here, either:

Details from the manufacturer:

This UV meter detects both atmospheric UV-A and UV-B light (ranging from 400 nm to 280 nm) and displays the current unified atmospheric UV index of both UV-A and UV-B. UV-A and UV-B are the UV rays that penetrates the atmosphere. Students then can relate this numerical index to our color changing UV beads or our light sensitive Print Papers: how dark the color or how quick the change. Note: the meter is not sensitive to the rather narrow frequency of UV light emitted from artificial sources such as a UV flashlight or UV lamp. Meter requires a 3 volt CR2032 button battery (included).

Sadly, you'll need a spectrophotometer. Spectrophotometry - Wikipedia, the free encyclopedia

Sorry, Lo_Volt, didn't see your post.

See #6 below for an interesting rebuttal to my post #4.

The meter is a fun tool to measure the intensity of the sun, for $32 instead of several hundred.....the second link shows how a student can build their own spectrometer with household items....the 2 together should yield the results desired....

Ultraviolet light covers the wavelength range from 100nm to 400 nm. The human eye sees light beginning at the blue end at 400 nm and extending to the red end roughly at 700 nm. The term nm is 'nanometers', a tiny fraction of a meter.

The UV region is divided into subregions, A, B and C. UVAB (UV A and B) covers the range from 280 nm to 400 nm.

The table below is copied from Wikipedia.

Ultraviolet UV 400 - 100 nm
Ultraviolet A UVA 400 - 315 nm
Ultraviolet B UVB 315 - 280 nm

Ultraviolet C UVC 280 - 100 nm

By the way - PLEASE BE CAREFUL using UV light. Do not stare directly at the light or at reflections of the light. Use a piece of window glass, at least 1/8th inch thick, in front of your eyes, or use goggles designed to block UV light. Strong UV light, or a long term exposure to it, can cause some eye damage.

Some dentists use UV light to cure dental adhesives, and they wear goggles or shields when using UV. You can ask your dentist to borrow a couple pairs of goggles or shields.

Your confusion comes from the sloppy shorthand (aka jargon) of the units of your instrument uses. UVAB is an inexact acronym contraction of the Ultraviolet A and B bandwidths. So your meter will only accurately measure light from 290 nanometers to 400 nm of wavelength. This is a given parameter and not something you calculate. (It would be a very useful part of your child's report for her to look up and quantify why light waves are measured in nm.) The brightness of this narrow bandwidth of invisible light is what this instrument measures in units of milliwatts per square centimeter.

I located several UVA filters on eBay. If you record the total light, add the filter, and measure it again, the remainder will be UVB and C, the difference being UVA.

There are some really smart people on this site, she had better win.

Nice to hear you have been helped in a positive way and are pleased with the results.

Quite often people who post 'homework' on questions on CR4 get sent off with snide remarks and a flea in their ear.

Just to re-emphasise the point: nm are units of length, and therefore suitable for expressing wavelengths of light and so its colour, but mW are units of energy, and will be more associated with the brightness of the light than with its colour. The two are completely independent of each other.

We really can't nail this down anymore without knowing the intention of the "science experiment".....the grade level of the student.....and the budget to work with....

Here are some guidelines...

http://coolcosmos.ipac.caltech.edu/cosmic_classroom/multiwavelength_astronomy/multiwavelength_astronomy/activities.html

https://www.aiha.org/get-involved/VolunteerGroups/Documents/NONIONRAD-UVRadiationQuickReferenceGuide.pdf

Perhaps this will help. The light meter you bought measures the intensity (or brightness) of a specific part of the light spectrum. The average human eye will "see" wavelengths between 4000 and 7000 nM - the colors deep purple to deep red (or ultra violet to infrared). The General Tools UVAB light meter will tell you how the amount, or volume of a particular wavelength increases or decreases. This functions similar to a radio - it reacts when the right frequency (or range of frequencies) hit the light detector, or "antenna". The amount of UVAB light intensity is displayed in mW/CM2 (how much energy is concentrated per square cm of area). This is one of two different aspects about energy. Your second reference (nm) refers to the wavelength, or frequency (color) of the energy. As other members have indicated, your meter will monitor a specific portion of the "energy spectrum" - google that for an eye-opening explanation of all the types of energy we benefit from.

The short answer is that mW/cm2 tells you how bright the light source, and nm tells you if the energy is of a wavelength you can see or if it is outside the frequencies our eyes can record - like the difference between a light bulb and the energy produced by a microwave oven or the energy that provides music from a radio.

This is from someone with a bit of laser and optics background.

WOW -- thank you CR4 community for your kind responses. Sadly, my ignorance in science clearly shows so fortunately at least I have a more successful career in art!

My 10 yo was able to use the General Tools meter to measure the reduction in light that different colored (but same material) t-shirts provided. To her surprise, her hypothesis that a white shirt would prevent more light from reaching skin was incorrect and that a blue shirt prevented the most light. She loves science and math so it is a good learning process.

We used the inexpensive uv index meter to figure out a range of mW/cm2 that related to UV Index composite so she could comprehend it better in simplified UV index terms rather than the complex mW/cm2 measurements. While unlikely the best way to calculate this, it was a good science experiment for her.

Again, thank you all for your time and effort to help the artist and aiding an aspiring scientist/dancer student! Cheers all!

artmom,Great job.

Hats off to you both. The T shirt "filter" idea is very creative.

Tell your daughter to notice the next time you're by the ocean, the color of sail covers on sail boats that are docked. Blue.