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LED Solar Lighting Guide

Key Advantages of Led lights for Solar Lighting
  • Led lights don't waste as much electricity as other types of lighting because a light emitting diode only emits photons from it's the front surface, not the sides or back. Other types of lighting emit light in all directions and much of it is wasted.
  • They also convert more energy to light with less wasted energy as heat.

How to measure LED light brightness
Lumens
The old light bulbs could be rated according to their power consumption in watts, we knew that a 100W light bulb was brighter than a 60W bulb, but with Light emitting diodes this does not readily apply, The correct measurement of light power is the Lumen (Lm), it is a measure of the total amount of light produced.

Lux
But just knowing the total amount of a light produced, the lumens, can be misleading. For example a light might produce 100 lumens but  the further that light travels outward the dimmer as it gets. Distance from the light source matters too so we need to know how brightly a light illuminates a particular surface when that surface is a certain distance away from the light source. We need to measure the illuminance and the unit is called the Lux (Lx). It measures the intensity of light falling on a surface. This is the parameter you need to know when selecting an led for solar lighting in order to conserve solar power.

Beam spread angle
The amount that the light diminishes as it travels from the light source depends on how much the light spreads out. CFL and Halogen lights have a 360° beam spread, emitting light in all directions. Led's are less wasteful as their beams are directional, at most spreading out about 120°. When comparing LED lights the beam spread should also be taken into account because the greater the beam spread the quicker the lux levels will drop as distance from the source increases.
For example, a particular led light might produce 300 lumens with a beam spread of 120°. As the light travels further away from the light source it spreads out and becomes dimmer and the the lux level rapidly decreases. If the same 300 lumen light had a beam spread of 60° the lux levels would be roughly doubled.

Comparing led lights to halogen and CFL lights
In order to compare real life light brightness levels the lux levels of difference types of lights were measured.

  1. 15W standard halogen reading lamp.
    The lux level was measured with the light bulb mounted in a fixture with reflector. At a distance of 1 meter from the light bulb the light level was 200 lux, bright enough for fine print reading. At 2 meters it was 50Lx, though not as bright, it  was still bright enough for general reading.
    Without reflector
    The same halogen bulb was later removed from the reflector fixture and showed the following light levels: 50Lx at 1m and 16Lx at 2m, illustrating the importance that the light reflector plays.
  2. 20W compact fluorescent (CFL) ceiling light
    In a room with white ceiling and walls, it showed light levels of 40Lx at 1 meter and 15Lx at 2 meters. This CFL is suitable for general room lighting but not for reading.
    Without reflection
    The same CFL light was later tested with dark sheets covering the walls and ceiling so as to remove as much reflection as possible, it had the following light levels: 25Lx at 1 meter and 7Lx at 2 meters.

The 20 watt CFL has similar brightness to a 4 watt LED light which only uses about one quarter of the electrical power because the light has a beam spread of 120° and very little is wasted light, and the light emitting diodes waste very power as heat. This is why LED lights are much better suited for solar lighting.

Lumens and watts can be misleading, remember the following:

  • Watts are not recommended when evaluating led light power.
  • Lumens can be misleading because of differences between types of lights and fixtures.
  • Lux levels are more practical when assessing the suitability of led lights.
  • Note the beam spread as well when choosing a light for general lighting.

We take actual lux measurements of our led lights and include those readings in the product specifications so you can make an educated decision when choosing an led light for solar lighting.