Read up on enough LED grow light sights and you’ll start picking up on beam angle. Beam angle is a way to describe how fast the light spreads out as it leaves your grow light.
A good example of a very tight beam angle is a laser pointer. Laser light beams exit the laser pointer all in the same direction, which is why you can point the pointer across the room and see a tiny red or green dot. The opposite end of the scale would be a old fashoned screw-in light bulb, which puts out light in all directions except for the base.
Many HID lights have very good reflector assemblies that focus about half the light into a narrow field and beam angle for this portion of the light may be as little as 10 degrees. And because of the way HID lights are designed they are very good for whole room grows.
LED lights work a little different. LEDs contain a part called a die that when current is passed through, emits light in one band. Then the light is spread with a lens – the domed part of the LED.
The chart above shows the beam angle of the LEDs we use in our grow lights. It shows full brightness dead center then as the angle from center increases the brightness decreases. The LEDs show a sharp drop in brightness at +/- 40 degrees from center. Even though brightness drops off sharply past +/- 40 degrees from center these are considered +/- 70 degree beam angle LEDs by the manufacturer because the light does not completely drop off until +/- 70 degrees.
Why is Beam Angle Important
Light from the sun has a beam angle of close to zero because by the time sunlight hits us it’s all traveling in a straight line. But all lights except for the laser pointer I mentioned above have a beam angle that’s greater than zero even though the angle may not be advertised.
Beam angle is impotant because the greater the beam angle the faster the light disperses or spreads out and this affects light penetration through the plants you are trying to grow. With a beam angle of 90 degrees (+/- 45 degrees), for every time the distance is doubled from the light the brightness is reduced to 1/4. Using this example – if the light you are using measures 1000 lumens at 1′ then the same light will measure 250 lumens at 2′, and that’s with no plant leaves in the way.
When Beam Angle is Important
Beam angle is very important when you are growing plants in a grow room where there is a lot of floor space with no plants. Or if you grow a solitary plant in a room where the light is allowed to spread out.
When Beam Angle is not Important
But beam angle is not important when you grow inside a small closet, cabinet or grow tent. This is because the walls of the cabinet work like giant reflectors – they bounce the light back to the plant.