Ask Helena & Leo

Question: I am interested in knowing if there’s a definition for the word “visible” as used in IPC/WHMA-A-620 where some target criteria states “visible”, does this mean unaided?

Answer: I dug the definition off the web from Merriam-Webster Dictionary:

Visible

1
a : capable of being seen
b : situated in the region of the electromagnetic spectrum perceptible to human vision —used of radiation having a wavelength between about 400 nanometers and 700 nanometers
2
a : exposed to view b (1) : conspicuous (2) : well-known
3
a : capable of being discovered or perceived : recognizable

There is no definition of visible in the T-50 which is the IPC Dictionary.

Using the above definition that something is capable of being seen, then one must use Table 1-2 Magnification Aids accordingly, especially paragraph 1.17.1.2 Magnification Aids, to determine whether or not the condition should be checked with the naked eye or have some degree of magnification to make the conditional determination.

According to the table anything larger than 0.064” can be seen and inspected with the naked eye. Between 0.064 and 0.025”, then mag lamps can be used.