Be Aware of the Downsides That May Exist in Lamps with High Transmittance
Before buying LED lamps, purchasers tend to inquire about the transmittance of the lamp lens, because many generally believe that the higher the light transmittance of the lens, the higher the light efficiency of the lamp, which would means in turn that the light fixture would save more energy. Research and sales show that when purchasers discover that the transmittance is above 93%, they tend to show more interest in the light products. However, as every coin has two sides, when you get high transmittance, there is also a down side and you should be aware what you may sacrifice.
As we know, the function of the LED lens is to adjust the emitting angle of the light source through refraction, so that the light type can better meet the required needs. The most common LED lenses are made from: Silicone, Glass (borosilicate ), acrylic (PMMA) and PC.
Silicone: The chemical stability of silicone is very good, as even at high temperatures silicone is not prone to qualitative change. The light transmittance of the silicone is very high, and can usually reach 95-98%, but silicone is very soft and its mechanical strength is very poor. It is not an ideal choice for the surface material of a lamp. Silicone lens are usually used as the first optical lens material in the LED chip as packaging (so that the light emitted will not run around).
Glass: The main components of glass are silicone and some metallic substances (such as B, P, Pb, Mg, etc.). Glass is currently the most ideal optical material because it has features such as high thermal resistance, low expansion coefficient (it is not prone to deformation), chemical stability (resistance to corrosion and yellowing), and glass lens can achieve a very high transmittance.
There are some shortcomings when the glass is processed into an aspherical shape, however, as it is difficult to control the precise shape, and accuracy can be low, so glass lenses are mostly adopted in a Lambertian distribution in which the light distribution is even in every direction. In addition, glass processing is difficult, production efficiency is low, and the cost is therefore higher. Further, not all glass has high transmittance, as there are some suppliers who adopt glass with a high level of impurities (usually a high percentage of lead) to save cost. Observed through the cross section, glass with high impurity content tends to be green, while glass with high transmittance tends to be white.
Acrylic: Acrylic is another common lens material is, also known as plexiglass, which is well known for high transmittance (usually more than 93%) and high production efficiency. As it can be made through injection molding (injection), the cost is low. The disadvantage is it has poor impact resistance and poor high thermal resistance, as usually 70°C is the highest temperature it can resist, and at over 80°C it will deform.
PC: PC lens is also a popular material and from its appearance, it is similar to the acrylic lens. The processing cost is relatively low and mechanical strength is high, with good thermal resistance (usually it can resist temperatures up to 130°C). The disadvantage of PC lens is that the transmittance is usually around 87%, lower than other common materials.
In conclusion, every type of LED lens has its own advantages and disadvantages. When you are evaluating a lamp, you should balance the advantages and disadvantages of the lens, rather than blindly pursuing just those with high transmittance. To achieve high transmittance, some manufactures sacrifice other properties of the lamp, which can lead to the defects in some other parts of the lamp.