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Light Wavelength

EmeraldW

New Member
Can you change light's wavelength by passing through a color lens? We are working with some plant species that do better under red and blue wavelengths.(no not the green sticky icky kind) :)

Is placing a red or blue lens between the light source and the object the same as having a red or blue light(LED)?
 

BrownOut

Banned
Is placing a red or blue lens between the light source and the object the same as having a red or blue light(LED)?
Pretty much. You're not exactly changing the wavelength. You're filtering out the undesired wavelengths. It would be the same as just having a red or blue LED, depending on the quality of the filter, or course.
 

EmeraldW

New Member
What would be considered good quality?

Would using a plain piece of red plastic at least put it in the ballpark?

Does it also filter out UV light?
 

BrownOut

Banned
I don't know how pure you need for your light to be. But an LED can put put a pretty narrow spectrum, and I'm not sure that can be achieved with a plane piece of red plastic. You either need a filter with specifications or a means to measure the light spectrum. BTW. decent spec'd light filters are pretty cheap. I'd do some sniffing around if I were you.
 
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crutschow

Well-Known Member
Most Helpful Member
Glass will filter out some of the UV but I don't think plastic will.
 

Sceadwian

Banned
EmeraldW, it depends on what you need, more of the specific light colour or blocking out of other colors. A filter will do absolutely nothing to increase the level of red or blue light provided from any source, but it will block the other one's as BrownOut stated, the question being is it these other colors of light that are bad for the plant or that the specific blue/red you're looking for is better for the plant? That needs to be clarified or there's no way to suggest what's best. Brownout's more than right about the spectrum of LED's they're VERY narrow, so narrow in fact you need to specify the specific range your plants like or you may chose the wrong LED's.

Flourescent bulbs are relatively 'peaky' in their spectrum, could be outside of the range you need, if this if for plant growth then you'd generally use 'grow lights' which is nothing more than a specialized phosphor blend to produce the broadest range of spectrum, the plant takes what it needs, though again this is different if there are specific parts of the spectrum that cause damage to the plant that you're trying to avoid. If it's UV specifically that you're trying to avoid there are sprays you can get that will go over any plastic/glass surface that block UV.

If all you're trying to do is block the UV then a UV blocker is all you need, again a filter will do NOTHING to produce more of a particular spectrum of light, in fact even the best filters will still block at least some of the desired spectrum.
 

jpanhalt

Well-Known Member
Most Helpful Member
No, you cannot change light's wavelength by any passive filter. You can change it by using an active filter, such as a fluorescent material. Typically, that results in a longer wavelength (i.e., 2 photon fluorescence is not common).

John
 

squishy36

New Member
Typical optical and UV LEDs that I have measured have FWHMs of 10-20 nm. If you e.g. put a blue filter in front of a red LED, you're not going to get any useful output.

If you need to filter out UV, plastics like polycarbonate are excellent UV filters.
 

EmeraldW

New Member
After thinking about it I guess the most important thing is filtering out the UV light. The plants we are working with react differently to different wavelengths and we wanted to be able to use certain ones at different times. I have put together a LED board to try that out for now. I will see what I can come up with to filter the UV light from the grow lights.
 

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