# How to measure blue light at home?

I know that we can measure light intensity using a simple 'light meter' and I know that 'blue light' emitted by LCD monitors is in $400-470\,\mathrm{nm}$ spectrum. Since I have sensitive eyes, I want to measure 'blue light' in different lighting conditions.

So I'm wondering whether it is possible to measure it with simple and inexpensive home appliances? How?

Might not be the cheapest option, but this has the functionality you need.

First a get a silicon photodiode, http://www.osioptoelectronics.com/standard-products/silicon-photodiodes.aspx

Then get a blue light pass filter, http://opticalfiltershop.com/product-category/edge-filter/short-wave-pass-filters/

Now you make a circuit with a 1k resistor and connect this to the circuit in series with the photodiode. You can measure the voltage drop across this resistor and because you know the resistance you can calculate the current from the voltage drop.

Alternatively, you could make or purchase a nice photodiode (transconductance) amplifier if accuracy is important, http://www.ti.com/lit/an/sboa061/sboa061.pdf

Filters that pass blue light but block other wavelengths are hard to find. Another option would be to disperse the light over different angular ranges, for example shining the light on to a prism or CD. Then only putting the diode where you see blue light. This would be similar to making your own monochromator.

• Thanks for the tip. What is important for me is the relative values not absolute measurement. So regarding that I'm not much of an electronic savvy, what about buying a consumer light meter and putting a transparent colored plastic filter in front of it? – Jand Sep 26 '15 at 15:27
• If you get the transmission spectrum of the filter in the range of interest you could do that. Blue-pass red-green-IR block are hard to find. – boyfarrell Sep 26 '15 at 15:39
• Ok, which of the filters in opticalfiltershop is better to use? – Jand Sep 26 '15 at 15:48
• Well you need to look at the transmission graphs and select a filter which has very high values in 400 to 470 region. But a word of warning, you might have to use a second filter to block out the IR because the blue filter tend to transmit again towards the red end of the spectrum. So pick a short wave pass that lets blue though and combine it with a red-IR block. – boyfarrell Sep 26 '15 at 16:02