The limitation of the original definition of the contrast brings about the misconstruing of computing method of panel contrast in some cases where the display effect of LED panel to be appraised. Because of the existing of the misconstruing in some cases

two problems have to be solved primarily in this paper.Generally

the display effect of the LED panel is influenced by many factors (indexes)

such an stability

luminance

chromo-contrast

visual angle

etc. But the main indexes inducing the misconstruing mentioned above are contrast and visual angle. So

first of all

the relationship between the contrast calculated by the test method of the LED panel and the visual angle need to be analysed

and a new index

so-called the contrast distributed at any visual angle

must be established to present the relation of the both indexes. As the same act of other indexes

the new index will be used to evaluate the display effect of the LED panel. So at first

the maximal panel brightness and the minimal panel brightness at any visual angle can be measured by BM-7 under a certain illumination intensity

and the contrast at any visual angle will be calculated. On the other hand

the contrast can be calculated by the expression of the test method of LED panel. By comparison

the difference between the results calculated by the both methods mentioned above exists

and the difference is very obvious. The experimental results indicate that the values of the contrast at any visual angle between that computed by LED panel measurement method and that calculated by the real panel brightness are also diffe-rent

and it was also proved that the results from LED panel measurement method are out of accord with the real display effect of LED panel.Secondly

the reason why the computing method is out of accord with the real display effect is due to the complex factors in the real surroundings. So the model of the main external factors which effect the values of the contrast in the real conditions must be analysed in detail

such as the measurement angle and the reflection parameters of extraneous light. Using the module of the reflection parameters

the minimal brightness curve of the extraneous light can be obtained.And comparing with the values measured by BM-7

it is concluded that the main characteristic consistence of two kinds of the curves obtained by different methods exists. Based on the conclusion

using the mo-del of the external factors

a new expression of the contrast can be established to evaluate the display effect of LED panel. And by using this new function relation

the curved surface of the contrast at any visual angle can be simulated. In comparing with the curve of contrast computed by the test method of IED panel

it was proved that the computing method of contrast in the test method of LED panel

as without thinking of the influence of specular reflection of extraneous light

is so idealization

sometimes its result could be not agree with the real display effect of LED panel. Thus

the misconstruing problem can be explained and resolved.