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How Much Light Does Glass Block?


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#1 foxman711

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Posted 23 November 2010 - 11:42 AM

In the summer I need my air-cooled hood, but not now. Does anybody know how much light is blocked by the glass?

#2 LITLJON

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Posted 23 November 2010 - 12:07 PM

In the summer I need my air-cooled hood, but not now. Does anybody know how much light is blocked by the glass?

Now about the glass. Glass is transparent because it lets all the colors go true it but what we can not see is that it acts as a filter for UV light. Most of UV radiation is stopped by glass & this is why you will not get sunburns behind a glass.

The glass simply filters out the UV radiation that is responsible for the sunburns & protect your skins from these energetic & somewhat harmful radiation. Sunblock lotion works exactly the same way, they simply filter out UV light.

I read somewhere that some UV causes increased resin production at the end flowering.

Thousands of different substances are used to make various forms of glass. How much and what type of light is transmitted depends on the type and purity of the substance used. Silica, in its purest form, transmits light well. Very little of the light wave is absorbed, but some of it is usually reflected. Look at almost any window and you will see this is true.



#3 Grow Thread

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Posted 23 November 2010 - 12:30 PM

glass in your hood............ if you need it , use it............ if you don't, don't.

#4 The Digital Nomad

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Posted 23 November 2010 - 12:50 PM

the amount of light blocked by the glass is not worth removing it from your aircooled hood. UV is not all good for plants, the harmful UV rays of the sun are filtered by the ozone, in the growroom - it is filtered by glass. Some MH bulbs can explode, the aircooled glass lens will keep it from shattering all over your grow.

The UV stuff you mention is perhaps more of a bulb change than simply removing glass - you can get bulbs in the 10,000 kelvin range and use it for the last half of your flower. Instead of expecting growth change in your grow room by removing the glass len, you could try adding another K range bulb. I use both a MH and HPS bulb in the flowering stage - both 3000k and 6500k. You could in theory flower with a 3000K bulb, and add a 10,000K bulb for the last couple weeks of flower for this 'increased resin output' experiment.

It is interesting to note that coral growers say that at 20,000 kelvin - growth slows or stops. The best PAR to use is still about 2,700K to 3,200K for flower and around 6,000K for veg. You can add a 10,000K bulb, but you should still have the required bulbs running in the best PAR range. What the plant uses for energy is more than just adding all these light waves - and UV is just another light wavelength.

Also:
* The lower the "K", the more yellow, then red the light appears, such as a 3000 K bulb.
* The higher the "K", the bluer the light appears, such as a 6500 K bulb.
* Sunlight (1 hour after dawn) = 3500 K
* Typical summer light (sun + sky) = 6500 K

Make sure you read up on Lumens, PAR, Watts, Kelvins/nano, etc - see how they all work together - not one can be omitted for a proper grow light.

-DN

#5 thanks2

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Posted 23 November 2010 - 12:54 PM

Glass reflects about 10% of the light. This lose is off set by the ability to bring the light closer to the plants. Since light intensity is a function of the inverse square law, there is a huge gain by having a air cooled fixture. Also, if the bulb explodes, it is easier to clean up.

#6 The Digital Nomad

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Posted 23 November 2010 - 01:04 PM

. Since light intensity is a function of the inverse square law, there is a huge gain by having a air cooled fixture.


I wanted to expand - you are talking about the loss of lumens as you get further away from the light source. And its true that aircooled lights allow plants to get closer to the light without burning!

A 80,000 lumen bulb is 80,000 at one foot. At two feet, due to the inverse square law thanks2 mentions, it is only going to be 20,000 lumens. Without an aircooled lense, you would have to keep your plants at about 2 feet away from the light! For best growth, they suggest at least 10,000 lumens - anything less than 10000 lumens is just going to be lanky, airy, and weak.

I can grow plants inches from the glass lens, and get more of the plant under the useable lumens range of the light. Also - after reading about heat problems in other people's grow rooms - the aircooled system is an enclosed system to catch and move heat from the lights. I use rigid ducting hooked up to two 600watt Easy Cool 8s, and the temp is only .5 degrees warmer than ambient temp in the grow. No A/C due to cooler air now, but still make sure you intake cooler air - not hot air from the furnace!!

-DN




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